X Dedication of The Institute for Theoretical Physics

X DEDICATION OF THE INSTITUTE FOR THEORETICAL PHYSICS Tale ved Indvielsen af Universitetets Institut for teoretisk Fysik (3. Marts 1921) Speech iit the Dedication of the Institute for Theoretical Physics (3 March 1921)

TEXT AND TRANSLATION*

*

[See Introduction, sect. 14.1

THE CORRESPONDENCE PRINCIPLE

Som jo Navnet paa denne Bygning allerede angiver, er den indrettet som et Institut for teoretisk Fysik, d.v.s. ti1 Hjemsted for Undervisningen og Studiet af dette Fag her i Landet. F$r jeg naermere omtaler Instituttets Oprettelse og Indretning, tdr det maaske vaere formaalstjenligt, at jeg begynder med at sige et Par Ord om det naevnte Fags Art. Ved Fysik forstaar man jo Laeren om Naturfaenomenerne eller, snaevrere, Laeren om de almindelige Love, der gzlder for den ikke organiske Natur. Ved fysiske Unders4gelser har nu forskellige Fremgangsmaader vist sig frugtbare ; dels har det ofte vaeret muligt direkte at sp4rge Naturen ti1 Raads ved Anstilling af fysiske Eksperimenter, dels har det vaeret muligt at opnaa Indsigt i Naturlovene ad mere filosofisk teoretisk Vej, hvorved man er gaaet udfra det almenmenneskelige Haab, at det er muligt at “forstaa” Naturfznomenerne, d.v.s. at finde simple, almene Love gaeldende for disse. De to Unders4gelsesmethoder er imidlertid ikke saa forskellige, som de i f$rste Qjeblik kunde synes, idet filosofisk Tankearbejde jo ogsaa ligger ti1 Grund for eksperimentale Unders$gelser, idet det er n$dvendigt at danne sig en Forestilling om, hvilke Sp4rgsmaal man b$r stille ti1 Naturen for at kunne haabe at faa et frugtbart Svar. Udfra Erkendelsen heraf kaldes ogsaa paa engelsk a1 Fysikstudium for Naturfilosofi. Alligevel har det ikke kunnet undgaas under Fysikens Udvikling, hvor saavel Erfaringsmaterialet som Tankebygningerne har naaet saa stort et Omfang, at det har vaeret mere og mere vanskeligt for en enkelt Mand at beherske de forskellige Omraader. Indtil for kort Tid siden doceredes dog Fysiken ved de fleste Universiteter af en enkelt Lzrer, og et saerlig smukt Eksempel paa, hvorledes dette har kunnet lade sig gdre paa heldig Maade, besidder vi i den for faa Aar siden afd$de Professor Christiansen, som for mange af 0s har vaeret den beundrede og dybt savnede Laerer. I Erkendelsen af Betydningen for Fysikstudiet af ikke alene at beskaeftige sig med det i Tidens L4b indh$stede Erfaringsmateriale, men ogsaa med den n$jere Udformning af de teoretiske Forklaringsbestraebelser, f4rtes Christiansen

THE CORRESPONDENCE PRINCIPLE

ti1 at paatage sig det store Arbejde, sideordnet med Undervisningen i Eksperimentalfysik, for Fysikstuderende at indrette en saerlig Undervisning i teoretisk Fysik, og Professor Christiansen omfattede. dette sidste Laerefag med en saadan Kaerlighed og Interesse, at han foruden sin velkendte Laerebog i Eksperimentalfysik, der den Dag i Dag bruges ved den polytekniske Laereanstalt, ogsaa har nedlagt et stort Arbejde i Udgivelsen af en Laerebog i teoretisk Fysik, ved hvilken han har haft saa lykkelig en Haand, at denne Bog stadig har kunnet udkomme i nye Udgaver og ikke alene bruges herhjemme af de fysikstuderende, men ogsaa bruges Verden over ved mange forskellige Universiteter. Det var derfor en naturlig Konsekvens af Christiansens staerke Fremhaevning af Betydningen af den teoretiske Fysik som saerligt Undervisningsfag og Fglelsen af, hvor vanskeligt det var under Fysikens stadig staerke Udvikling for en enkelt Mand at overkomme at repraesentere begge Sider af Faget, at der kort efter hans Afgang fra Universitetet foruden det gamle Professorat i Fysik, som det lykkedes at besaette med en saa fremragende Eksperimentalfysiker som Professor Martin Knudsen, oprettedes en ny Laererstilling, et Professorat i teoretisk Fysik ved Universitetet, og det er med stor Glaede, at jeg kan meddele, at vi paa Instituttet her, lige saa vel som ved Universitetets Fysikinstitution paa den Polytekniske Laereanstalt, besidder et synligt Minde om Professor Christiansen, idet en af Professor Christiansens Elever og Beundrere har foraeret 0s det vellignende og smukke Billede, som Fr@kenColsmann har udfgrt af Professor Christiansen i dennes sidste Dage, og som De vil faa at se ophaengt i Instituttets Bestyrervaerelse. Ved den nye Laererstillings Oprettelse var der ti1 at begynde med intet Znstitut knyttet ti1 denne, men Trangen dertil meldte sig straks, idet det, selv om det er paakrzvet at have en Laerer, der saerlig har beskaeftiget sig med og er inde i den teoretiske Fysiks Metoder, dog ikke er muligt for en saadan at opnaa fuldstaendigt Udbytte af videnskabelige Unders$gelser, naar der ikke er Lejlighed for ham eller hans Medarbejdere ti1 at anstille eksperimentelle Undersggelser. Dette haenger sammen med, at det, saaledes som det Gang paa Gang har fundet Sted i Fysikens Udviklingshistorie, ofte har vaeret muligt gennem teoretiske Betragtninger og Undersggelser at aabne nye Omraader for frugtbar Eksperimentalforskning; men herved vil det ofte vaere Tilfaeldet, at kun den, der besidder indgaaende Kendskab ti1 Teoriens Grundlag og Resultater, vil vaere i Stand ti1 at overse, hvorledes saadanne Undersggelser anstilles med bedst Udbytte, og navnlig galder det paa et Tidspunkt som det nuvaerende, hvor det har vaeret muligt ad Tankeveje der f$rst er betraadte af de store tyske teoretiske Fysikere Planck og Einstein at opdage, at visse af de Grundsynspunkter, hvorpaa fysisk Forskning i lange Tider har vaeret baseret, ikke uden gennemgribende Forandringer kan anvendes ved Studiet af Bevaegelserne af Partiklerne i Atomernes Indre; og hvor Undersggelser over Atomspgrgsmaal netop nu drives med saa

THE C O R R E S P O N D E N C E P R I N C I P L E

stor en h e r , og som i visse Henseender har bragt netop den teoretiske Fysik saa staerkt i Forgrunden, staar man ved de teoretiske Unders4gelser stadig overfor Sp4rgsmaal om, hvorvidt de benyttede Antagelser er overensstemmende med Virkeligheden, og man er under Arbejdets Fremadskriden stadig henvist ti1 at lade Naturen selv afg$re saadanne Tvivlspdrgsmaal ved Anstillelsen af Eksperimentalunders4gelser. I Erkendelsen af det berettigede i disse Krav mddte Forslaget om Oprettelsen af et Institut ogsaa udelt Tilslutning ved sin Fremkomst ved Universitetet, hvor det j o som alle saadanne Forslag f$rst behandledes i Fakultetet af Fagfaellernes Kreds, og jeg vilde gerne her straks udtale min Tak navnlig ti1 Fakultetets to Repraesentanter i Konsistorium, Professor Biilmann og Professor Johannsen, der fra f4rste Faerd hver isaer paa mange Maader har vaeret behjaelpelig saavel ved Planernes f4rste Udarbejdelse som ved deres Gennemf4relse. Men forend Sagen blev faxdig behandlet ved Universitetets hojere Instans, Konsistorium, skete der noget, som vaesentlig bidrog ti1 Sagens Fremme, nemlig det at der fra privat Side vistes en offervillig Interesse for Instituttets Oprettelse. Dette skete paa den for mig overordentlig morsomme og opmuntrende Maade, at en Skolekammerat og Ven, Direktdr BerlPme, der havde hprt om Forslagets Fremkomst, henvendte sig ti1 Professor Faber, der paa det Tidspunkt var Universitetets Rektor, og spurgte ham, om han mente, at det vilde tjene ti1 Sagens Fremme, om der fra privat Side kunde stilles Midler ti1 Raadighed ti1 Hjaelp for Planernes Udf4relse. Efter at Professor Faber svarede, at han f4lte sig overbevist om, at dette vilde vaere Tilfaeldet, dannedes der en KomitP med Direkt4r Berleme som Kasserer, hvori Direkt4r Harald Plum, Ingeniqir N. M. Plum, Konsul Hey, Bankier Goldschmidt, Direkt$r Siegumfeldt, Professor Faber, Professor H$ffding og den nylig afdgde Professor Troels Lund indtraadte, og som satte sig i Spidsen for en Indsamling indenfor en snaevrere Kreds, hvorved der indkom t:t Bel4b af Kr. 80,000.- , Dette Resultat har ikke alene vaeret af Betydning soin Vidnesbyrd for offervillig Interesse for en Sag af saa almen Karakter, men har vaeret af den mest direkte Nytte for Instituttets Oprettelse, idet det for denne Sum lykkedes ti1 Universitetets Disposition at stille den udmaerket beliggende Grund, hvorpaa denne Bygning nu staar, og som tilh4rte Kq4benhavns Kommune. For den lykkelige Afslutning af de ti1 denne Ejendoms Overdragelse knyttede Forhandlinger og for det store Arbejde, han har nedlagt deri, skylder Instituttet Professor Faber megen Tak. De Midler. der blev stillet ti1 Raadighed ved den naevnte Indsamling, var jo dog kun en forholdsvis ringe Begyndelse, og for den Interesse og Velvilje, som Sagen har m$dt fra Regering og Rigsdug, der f$rte ti1 Bevilligelsen af de ti1 Opf4relsen og Indretningen kravede Midler, vil jeg gerne paa Instituttets Vegne overfor de mddte Repraentanter for Regeringen og Lovgivningsmagten udtale

THE CORRESPOKDENCE PRINCIPLE

vor store Taknemmelighed. Nu ligger altsaa Instituttet her, og selve Bygningens Tilblivelse skyldes Bygningsinspektqir Arkitekt Martin Borch; og paa de Menneskers Vegne, der skal faerdes og arbejtle i disse Rum, vilde jeg gerne overfor Arkitekt Borch udtale vor taknemmelige Glaede over de smukke Omgivelser, han har skabt for dette Arbejde, og den udrrizrkede. formaalstjenlige Maade, hvorpaa han har vidst at anvende de bevilligede Midler. I denne Forbindelse vil jeg ogsaa gerne have Lov ti1 at bringe vor bedste Tak ti1 Arkitekt Borchs Medhjaelper ved det daglige Arbejde, Arkitekt Munch, hvis Opfindsomhed og Taalmodighed Gang paa Gang er blevet sat paa den staerkeste Prqive ved de mange stadig opdukkende nye Krav, som Anbringelsen og lndretningen af de talrige af de videnskabelige Unders4gelser kraevede Installationer har medf4rt. Hvad Bygningens Haandcazrksmazssige Udfdrelse og Indretning angaar, er Murerarbejdet udfqirt ved Hr. Murermester Poul Bagger, T4mrerarbejdet ved Hr. Tqiinrermester Valdemar Zeltner, Snedkerarbejdet ved Firmaet Julius Mqiller Rr Sdn, Blikkenslagerarbejdet af Hr. Blikkenslagermester Tofte, Malerarbejdet af Firmaet Christian Thorsen & Sdn, Gdrtlerarbejdet af Hr. Fabrikant Richard Wieder og Smedearbejdet af Hr. Smedemester Brnbak. Endvidere er det store Opvarmnings-, Ventilations- og Gas- og Vandanlaeg udf4rt af Firmaet Bonnesen & Danstrup og de elektriske Installationer af Firmaet Kemp & Lauritzen, der saavel har udfqirt Lysanlaeget som det komplicerede elektriske Anlaeg, krzvet ti1 Brug for de videnskabelige Undersqgelser. For den Elskvaerdighed, hvormed Ingeni$r Richter af dette Firma har stillet sin Indsigt ti1 vor Raadighed, vil jeg ogsaa gerne benytte denne Lejlighed ti1 at takke. Jeg vilde ogsaa gerne bede Hr. Murerformand Andersen som Repraesentant for Haandvaerkerne paa hans egne og Kollegers Vegne at modtage vor bedste Tak. Hr. Andersen selv har varet med i Arbejdet fra f4rst ti1 sidst og har ikke alene altid med stqirste Hum@ fundet sig i alle de Forstyrrelser i Murerhaandvaerket, som Anbringelsen af de mange R4r og Ledninger har foraarsaget, men endda altid selv med stqirste Elskvaerdighed har hjulpet med ti1 at anbringe de forhadte Installationer paa bedste Maade. Medens jeg taler om Instituttets Indretning, kan jeg ikke undlade at omtale den store Hjaelp, som Docent Dr. H . M . Hansen har ydet mig ikke alene ved Planlaeggelsen og Indretningen i store Traek, men ved Gennemtaenkningen af selv de rnindste Detailler, og jeg vilde gerne benytte Lejligheden ti1 at udtale den store Taknemmelighed, som mange af Fysikens Dyrkere herhjemme skylder Dr. Hansen paa Grund af hans stedse redebonne Tjenstvillighed og uegennyttige Interesse overfor saavel Elever som Kolleger, en Taknemmelighed som vi kun sjaeldent faar Lejlighed ti1 at udtrykke, og jeg vilde gerne samtidig udtale min Glaede over, at Dr. Hansen har i Sinde at deltage i det videnskabelige Arbejde

THE CORRESPONDENCE PRINCIPLE

paa det nu faerdige Institut, ved hvilket hans enestaaende Kendskab ti1 og Indsigt i spektroskopiske Unders4gelser vil vaere af den st4rste Vxrdi. Hvad Arten af de videnskabelige Arbejder angaar, hvorpaa Instituttet saerlig er indrettet, indtager netop spektroskopiske Undersbgelser den f$rste Plads. Dette hanger paa det n4jeste sammen med, at man i Unders4gelsen af det Lys, som Stoffet kan bringes ti1 at udsende, har et Middel af st$rste Vaerdi for Indhentning af Oplysninger om Stoffernes Sammensaetning og om Bygningen af Stoffernes Atomer. Denne Undersdgelse sker ved Apparater, der kaldes Spektroskoper, og De vil faa Lejlighed ti1 at se flere Typer af saadanne opstillede i Unders4gelseslokalerne. Den Type af Spektroskoper, der i mange Tilfaelde er den, der egner sig bedst ti1 finere Unders$gelser, er de saakaldte Gitterspektroskoper, og det er derfor af stor Betydning for os, at Carlsbergfondets Direktion har stillet en st$rre Pengesum ti1 min Raadighed ti1 Bygning og Opstilling af en stor Gitterspc2ktrograJ Gitteret selv vil ved denne blive anbragt i Bunden af en 20 Fod dyb Br$nd, der er bygget i et af Fors4gsrummene i Kaelderetagen. Gitteret selv har vi endnu ikke faaet, men venter det hvert Ojeblik, og De vil derfor i Dag kun kunne faa Br4ndkonstruktionen selv at se. Jeg vil gerne imidlertid benytte Lejligheden ti1 her i dette Rum at demonstrere et Gitters Virkemaade for Dem ved Hjaelp af et Antal smaa Gittere som dette, jeg her holder, og som om et Qjeblik vil blive omdelt blandt Dem. Disse smaa Gittere er Aftryk paa en Kollodiumhinde af et virkeligt Gitter, der er dannet ved at strege et overordentlig stort Antal fine, parallelle Streger paa en Metalplade. Stregernes Antal er meget stort ; paa et saadant Gitter er der streget ca. 1000 Streger paa hver mm. De smaa Gitteraftryk er kun anvendelige i Undervisnings$jemed, men er ti1 Gengaeld ogsaa ganske billige ; medens et virkeligt stort Gitter, brugbart ti1 videnskabelige Unders$gelser, koster adskillige tusind Kroner, har Firmaet Hilger i London, hvorfra den st4rste Del af det optiske Udstyr er anskaffet, leveret 0s disse smaa Gittere for ca. 1 Kr. pr. Stk. Vi har flere Dusin, men der er dog ikke tilstraekkelig til, at De allt: samtidig kan se i et. Hvad nu Gitterets Virkemaade angaar demonstrerer (det) sig simpelt ved et Par Tegninger. Paa denne Figur skal de vandrette Streger foroven forestille et System af B$lger, svarende ti1 B$lger der breder sig ud paa en Overflade, eller i vort Tilfaelde et System af Lysbqlger. Traeffer nu disse Bqlger en Plade, hvori der er et Hul, vil B$lgebevaegelsen forplante sig ind gennem Hullet ; men hvis Hullet er lille i Forhold ti1 Afstanden mellem B@lgerne, vil vi paa den anden Side faa et System af kugleformede Bdlger, saaledes som det er vist paa'den nederste Del af Figuren. Hvis det var en Spalte i Stedet for et Hul, vilde vi faa akkurat det samme at se; de enkelte B$lger vilde blot ikke blive kugleformede, men cylinderformede. Taenker vi 0s nu, at vi ikke har en Spalte, men et stort Antal Spalter, demonstreres Faenomenet simpelt ved denne anden Tavle. Der er her omkring hvert af Hullerne eller Spalterne tegnet et System af

THE CORRESPONDENCE PRINCIPLE

Cirkler ,ganske svarende ti1 Systemet paa den f$rste Tavle. I f$rste Qjeblik er det Indtryk en saadan Tavle frembringer, kun et Virvar; men ser man n$jere til, krystalliserer der sig visse regelmaessige Traek ud af dette Virvar. Vi ser f$rst og fremmest, hvordan vi hernede, hvor Cirklerne er st$rre, faar gendannet Linier, der svarer ti1 det B$lgesystem, vi vil faa frem, dersom Pladen med Spalterne slet ikke havde vaeret ti1 Stede; men dette er ikke det eneste simple B$lgesystem, der fremkommer ved Samvirken af den B$lgebevaegelse, der udgaar fra de enkelte Spalter. Vi ser her en Raekke Linier, der ligger skraat, og som danner et B$lgesystem, der forplanter sig i en Retning, der danner en Vinkel med de oprindelige B$lger og heret der ligger skraat ti1 den modsatte Side, og her igen et hvor B$lgerne staar endnu mere stejlt i Forhold ti1 de oprindelige B$lger og her atter et, der halder ti1 modsat Side. Idet nu de Vinkler, som de skraa B4lgesystemer danner med det oprindelige System, foruden af at Afstanden mellem Spalterne afhaenger af B$lgelangden, d.v.s. af Afstanden mellem de paa hinanden f$lgende B$lgeflader i det oprindelige, plane B$lgesystem eller i det System af kugleformede B$lger, der udgaar fra hvert enkelt af Hullerne, har man i et saadant Gitter et Middel ti1 at skille Lyset ad i dets forskellige Bestanddele, i dets forskellige Farver, og et Middel, der af Grunde, som det vil blive for langt her at komme ind paa, hvad Opl$sningsevnen angaar, er f. Eks. Glasprismer langt overlegent. Forstaaelsen af et Gitters Virkemaade skyldes Fraunhofer, der af mange Grunde t$r betragtes som Spektroskopiens Fader. Uddannelsen af Gitteret ti1 det Hovedhjxlpemiddel, som det er ved optiske Unders$gelser, skyldes den amerikanske Fysiker Rouland*. Hvis man nu igennem et saadant lille Gitter ser paa en Lyskilde, der som denne Traad naar den bringes ti1 at gl$de udsender Lys af alle mulige Farver, faar man et Billede at se, der svarer ti1 det, der er angivet paa denne Tavle. Man ser f$rst og fremmest lige igennem Gitteret svarende ti1 Rekonstruktionen af de oprindelige B$lgeflader paa den foregaaende Figur ; men dernaest opstaar der ogsaa B$lgesystemer, der b$jes ud ti1 Siden og er ulige staerke for de forskellige Farver; idet de blaa Straaler b$jes mindst, de r$de mest, ser man et Spektrum som det, der her er antydet. Udenfor det ser man endnu et Spektrum svarende ti1 de Bdlgesystemer, der blev b@jetendnu mere ti1 Siden, og som vi saa paa den forrige Figur; de er svage, og dem vil vi ikke faeste Opmxrksomheden ved. Havde vi nu imidlertid i Stedet for at rette Gitteret imod en Lyskilde som en gl$dende Platintraad rettet det imod et Udladningsr$r indeholdende en Luftart, vilde vi, naar der gik elektriske Udladninger igennem Rgret, faa noget ganske andet at se. Her vilde ikke Lyset indeholde alle Farver, men kun nogle enkelte Farver, og Spektret vil derfor ikke bestaa af et bredt Baand, men kun af enkelte adskilte Linier, saadan som de her er antydet lxngere nede paa Tavlen.

*

[Should read Rowland.]

THE CORRESPONDENCE PRINCIPLE

Nu vil de smaa Gittere blive delt om, men fgr vi gaar videre, vil det vaere beds: at rulle Rullegardinerne ned. Idet vi nu sender Strgm gennem Platintraaden, vil de, der har et Gitter, se dels Traaden som uden Gitter, dels Spektrene paa hver Side, de stxrke Spektre af fgrste Orden og de svagere Spektre af anden Orden endnu laengere ti1 Siden. Sender jeg nu Udladninger gennem dette Rgr, vil De i Stedet for de brede Spektre se et Antal Linier, saaledes som det var tegnet paa Tavlen. Ved Hjxlp af en Undersggelse af disse Linier er det, at det har vaeret muligt at opnaa en Indsigt i de Love, der gaelder for Bevaegelserne af Partiklerne i Atomerne. Dette Rgr indeholder f. Eks. lidt af den sjaeldne Luftart Helium, og et Studium af Heliumspektret har netop givet overordentlig vigtige Oplysninger ikke alene om Heliumatomets Natur, men endda belaert 0s om visse almene Love, som rnan tgr haabe vil hjaelpe 0s ti1 Forstaaelse ogsaa af Bygningen af andre Stoffers Atomer. Ved denne lille Afbrydelse i min Redeggrelse for Laboratoriets Indretning har De faaet Lejlighed ti1 at stifte Bekendtskab med nogle af de Midler, som staar ti1 vor Raadighed for Undervisningen. Som jeg fgr naevnte for Gitterspektroskopernes Vedkommende, er de optiske Apparater, der kraeves af videnskabelige Undersggelser, ofte meget kostbare, og det har vaeret meget vanskeligt at faa de bevilligede Midler ti1 at straekke til. I denne Forbindelse maa jeg naevne, at det har vaeret af stgrste Betydning for Anskaffelsen af vort Udstyr af optiske Apparater, at tler fra anonym Side er blevet tilstillet Instituttet en stor Gave af 10,000 Kr. ti1 dette Qjemed, som har gjort det muligt for 0s at anskaffe visse for Unders4gelserne meget vaerdifulde Apparater, som vi ellers havde maattet savne. Det har jo vxret en vanskelig Tid ti1 at anskaffe Apparater paa Grund af den uhyre Prisstigning i de sidste Aar, og i Anerkendelse heraf har Bevillingsmyndighederne ogsiia fordoblet det oprindelig bevilligede Belgb ti1 Apparater, der var anslaaet efter de fgr Krigen gaeldende Priser. En Tid lang saa det alligevel ud til, at det skulde blive helt galt for 0s paa Grund af Valutaforholdene, idet de i England bestilte Apparaters Pris steg i samme Forhold, som den danske Krone faldt. Denne Vanskelighed blev vi imidlertid bragt ud over gennem det xdelmodige Tilbud af Hr. Bunkier Torben Meyer af Firmaet Brgdr. Trier, der tilbgd at skaffe 0s tle engelske og udenlandske Penge, som vi skulde benytte ti1 Apparatanskaffelserne, ti1 Priser svarende ti1 de f$r Krigen herskende Valutaforhold, et Tilbud, der var ensbetydende med en Gave ti1 Instituttet paa mange tusinde Kroner. Trods a1 den Offervillighed, som saaledes fra de offentlige Bevillingsmyndigheders og fra privat Side er vist Instituttet, har det imidlertid ikke vaeret muligt at anskaffe et Apparatudstyr,som tillader 0 s at anstille Undersggelser over alle Dele af Spektret, der alle lige fra de allerlxngste Varmestraaler ti1 de allermest kortb4lgede Rgntgenstraaler hver i s m yder deres Bidrag ti1 at muligg$re en

THE CORRESPONDENCE PRINCIPLE

Indtraengen i Atombygningens Hemmeligheder, og hvis det skal vaere muligt for 0s at komme ti1 at raade over de paakraevede Hjaelpemidler ti1 Gennemf$relsen af alle de forskellige, ginskelige Undersgigelser i en ikke altfor fjern Fremtid, maa Staten eller private traede yderligere hjaelpende til. Ved Unders4gelser over Atomsp4rgsmaal er der imidlertid andre Veje at gaa end den, som Undersgigelser af Stoffernes Spektre frembyder. De af de tilstedevaerende, der i Torsdags havde Lejlighed ti1 at hgire Professor Francks Foredrag i Danmarks naturvidenskabelige Samfund, vil have h$rt, hvorledes det er lykkedes denne fremragende Fysiker og hans Medarbejdere at aabne en ny Vej ti1 Udforskningen af Atombygningen, nemlig ved Unders4gelser over Virkningen af Sammenstgid mellem Elektroner og Atomer, og det er en stor Lykke for Instituttet, at det for Midler, som nogle af de f4r naevnte Venner af Instituttet har stillet ti1 Raadighed, har vaeret muligt at indbyde Professor Franck ti1 at komme herop og ggre 0s bekendt med Resultaterne af sine betydningsfulde Undersgigelser og hjaelpe 0s med Instituttets Indretning og f$re 0s ind i de af ham udarbejdede, vanskelige Unders4gelses-Metoder ; et Apparat, der benyttes ved saadanne Unders$gelser, vil de tilstedevaerende finde opstillet i et af de tilst4dende Forsq5gsrum. Vi skylder imidlertid ikke alene Professor Franck Taknemmelighed for hans nu desvaerre snart afsluttede Bes$g, men det er for 0s alle her en af de Ting, hvortil vi glaeder 0s mest, at vi kan vente Professor Franck tilbage ti1 Efteraaret paa et gentaget Bes4g. Foruden Unders4gelser over St4dionisation er der endnu flere Omraader af Eksperimentalforskning, der har den ngijeste Tilknytning ti1 Spgirgsmaalet om Atombygningen, og f4rst og fremmest Studiet af de saakaldte radioaktive Stoffer. Ja, det vil jo vaere Dem alle bekendt, hvordan den geniale, engelske Naturforsker Sir Ernest Rutherford, der hgirer ti1 de allerst4rste af alle Tiders Fysikere, har vist, hvordan det er muligt udfra saadanne Studier at opnaa direkte Oplysninger om Atomernes Byggestene, ja Rutherford har givet Stgidet ti1 den hele nyere Udvikling paa Atomfysikens Omraade gennem sine Opdagelser vedrgirende disse Byggestenes Natur. Mange af de her tilstedevaerende vil have haft Lejlighed ti1 at h4re Sir Ernest Rutherford selv fortaelle om disse Underss4gelser ved hans Forelasninger paa Universitetet i September Maaned. Det var det oprindelige Haab, at Laboratoriet her skulde vaere saa tidligt faerdigt, at Indvielsen kunde finde Sted under Rutherfords Bes$g, hvad naturligvis vilde have vaeret en overordentlig Glaede. Paa Grund af Forsinkelser naaedes dette jo ikke, men vi er glade ved her ti1 Stede at have en anden Repraesentant for de Forskere, der har beskaeftiget sig indgaaende med radioaktive Undersgigelser, og som selv har udf4rt meget betydningsfulde Undersgigelser herover, nemlig Professor Hevesy fra Budapest. Professor Hevesy kom her ti1 Byen sidste Foraar paa det Tidspunkt, hvor vel

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ikke Laboratoriet kunde ventes at vaere fuldstaendig faerdigt, men hvor det dog var vort Haab, at de videnskabelige Unders$gelser her skulde kunne begynde. For dette Tilfaeldes Vedkommende har imidlertid Forsinkelsen af Laboratoriets Indretning haft en lykkelig F$lge for dansk Videnskab, idet Professor Hevesy fandt et midlertidigt Hjemsted i det fysisk-kemiske Laboratorium paa Polyteknisk Laereanstalt hos Professor Br$ndsted og sammen med denne sidste har paabegyndt og udf$rt de betydningefulde Unders$gelser, hvorom de fleste af Dem sikkert har hgrt Tale, over Grundstoffernes Adskillelse i Bestanddele med samme kemiske og fysiske Egenskaber men med forskellig Atomvaegt. Selv om dette lykkelige Samarbejde med Professor Brqhdsted sikkert og forhaabentlig vil blive fortsat, glaeder vi 0s dog ti1 ogsaa her nu, da Instituttet staar faerdigt for videnskabelige Unders$gelser, at kunne nyde godt af Professor Hevesys vaerdifulde Deltagelse i disse. Foruden de hidtil naevnte Videnskabsmand er det endvidere en stor Glaede, at jeg her ved Instituttets Indvielse kan byde et Antal yngre, lovende Videnskabsmaend, blandt hvilke der findes Repraesentanter fra vore Nabolande, velkommen ti1 Arbejdet her. Hvad det ti1 Instituttet knyttede, faste Personale angaar, er det endelig med den st$rste Glaede, at jeg kan byde Dem velkommen ti1 Arbejdets regelmaessige Optagelse og takke for a1 den Hjaelp, som De hver isaer har ydet ved Instituttets Indretning. Jeg vilde gerne szrlig fremhaeve, hvor lykkeligt vi er stillede ved som den f$rste ti1 Laboratoriet knyttede videnskabelige Assistent at have den unge hollandske Fysiker Dr. Kramers. Dr. Kramers har opholdt sig her i Landet i de sidste 44 Aar og har i den forl$bne Tid udf$rt et stort videnskabeligt Arbejde, som Anerkendelse for hvilket han blandt andet for to Aar tilbage erhvervede Doktorgraden ved Universitetet i Leiden. Lige fra jeg laerte Dr. Kramers at kende ved hans Ankomst her ti1 Landet, har jeg vaeret klar over hans store Evner, og paa Instituttets Vegne vil jeg gerne udtale, hvor glade vi er ved ti1 det at vide knyttet en ung Kraft, der ikke alene som faa er fortrolig med den teoretiske Fysiks Hjaelpemidler og Resultater, men ogsaa selv har ydet vaerdifulde Bidrag ti1 Belysning af netop de Sp$rgsmaal, vi saerlig taenker at beskaeftige 0s med her. Dr. Kramers har i de sidste Aar ikke alene vaeret mig ti1 stor Hjaelp ved mine videnskabelige Arbejder, men ogsaa ved Undervisningen og Vejledning af de studerende. Det sidste f$rer mig endnu engang ti1 at fremhaeve, at dette Institut jo ikke alene er indrettet paa den videnskabelige Forskning, men ogsaa skal tjene ti1 Hjemsted for Underuisning for Fysikere og andre specielt Fysikinteresserede, og jeg vilde gerne benytte Lejligheden ti1 at sige, at jeg tror, at denne Sammenknytning er et Moment af st$rste Betydning som Forvarsel for Instituttets lykkelige Trivsel. Ved videnskabelige Arbejder er det j o saadan, at ingen t$r give bestemte L$fter for Fremtiden; vi maa vaere forberedt paa, at der paa de Veje,

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som vi i dette Qjeblik tror at se ligge banede for os, kan taarne sig Hindringer op, der ganske spzrrer Vejen, eller ti1 hvis Overvindelse der vil krzves helt nye Tanker. Det er derfor af st$rste Betydning ikke alene at vaere henvist ti1 Evner og Kraefter hos en begraenset Kreds af Videnskabsdyrkere; men den Opgave at skulle f$re et stadig fornyet Antal yngre Mennesker ind i Videnskabens Resultater og Metoder bidrager i h$jeste Grad ti1 stadig at tage Sp$rgsmaal op ti1 Dr$ftelse fra nye Sider, og ikke mindst f$res der jo igennem de unge Menneskers egen Indsats stadig nyt Blod og nye Tanker ind i Arbejdet. Idet jeg afslutter denne Redeg$relse, vil jeg gerne samtidig med, at jeg udtaler Forsikringen om, at vi skal g$re vort yderste for at fors$ge at g$re 0s vaerdige ti1 den Tillid, der har fundet sit Udslag i den store Offervillighed, der er udvist saavel fra Statens som privat Side, udtale Haabet om, at dette Institut maa blive et Sted, hvor i Tidens L$b mange yngre Dyrkere af den fysiske Videnskab vil kunne finde Vejledning i deres Studium og Hjaelp ti1 at give deres eget Bidrag ti1 Fremme af vor Forstaaelse af Naturen og ti1 E r e for dansk Videnskab.

Translation This building, as its name indicates, is arranged as an institute for theoretical physics, i.e., as a home in this country for the teaching and study of this subject. Before discussing more closely the establishment and arrangement of the Institute, it may be appropriate that I begin by saying a few words about the nature of the subject mentioned. By physics we understand the science of the phenomena of nature, or, more specifically, the subject which deals with the general laws holding for the non-organic nature. Now, various procedures have proved fruitful in physical investigations; thus, it has often been possible to consult nature directly by carrying out physical experiments. In other cases, it has been possible to gain an insight into the laws of nature by a more philosophical or theoretical approach, in which the starting point has been the universal human hope that it is possible to “understand” the natural phenomena, i.e., to find simple general laws holding for them. However, these two methods of investigation are not as different as they might seem at first sight ; in fact, philosophical thinking provides a basis for experimental investigations, since it is necessary to form an idea as to what questions to ask of nature in order to have hope of obtaining fruitful answers. In recognition of this fact, all study of physics is in English called natural philosophy. Nevertheless, in the development of physics, in which the experimental material as well as the edifices of thought have reached such vast proportions, it has unavoidably become more and more difficult for a single man to master the different fields.

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Nevertheless, until very recently physics was taught in most universities by a single teacher. An especially fine example of how this could be done successfully we have in Professor Christiansen* who died a few years ago; for many of us he was our admired and deeply missed teacher. Recognizing the importance in the study of physics of not just dealing with the experimental material gathered through the years but also with the detailed formulation of theoretical efforts at explanation, Christiansen was led, alongside his teaching of experimental physics, to undertake the large task of arranging for special teaching of theoretical physics to physics students; Professor Christiansen embraced this task with such love and interest that, in addition to his well-known textbook in experimental physics, which is still used at the Technical University, he devoted a large amount of work to the publication of a textbook in theoretical physics ; he had such success with this book that it has constantly appeared in new editions, and it is used by physics students not only here but in many different universities around the world. It was therefore a natural consequence of Professor Christiansen’s strong emphasis upon the importance of theoretical physics as a special subject of instruction, and of the feeling of the difficulty, under the constantly strong development of physics, of one man being able to represent both sides of the subject, that, shortly after his retirement from the University, there was established a new teaching position, a professorship in theoretical physics, in addition to the old professorship which it had fortunately been possible to fill with such an eminent experimental physicist as Professor Martin Knudsen**. It is with great pleasure that I can tell you that, as at the University’s physical institution at the Technical University, we here at the Institute possess a visual memorial of Professor Christiansen, in that one of his pupils and admirers has presented us with the lifelike and beautiful painting made by Miss Colsmann of Professor Christiansen in his last days. You will get to see it hanging in the Director’s Office of the Institute. When the new teaching position was established, there was to begin with no institute attached to it; however, the need for it appeared at once; for, while it is necessary to have a teacher who has employed and is familiar with the methods of theoretical physics, it is not possible for him to make the most of his scientific investigations, unless he or his co-workers have the opportunity of carrying out experimental investigations. This is connected with the circumstance that, as has happened again and again in the history of physics, it has often been possible through theoretical considerations and investigations to open up new fields for fruitful experimental research; however, it will often be the case that only one who possesses ii thorough knowledge of the foundations and results of the theory *

**

[See Vol. I , p.xlx.1 [See Vol. I , p. [1091.]

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will be capable of seeing how such research can be carried out to best advantage; this is especially true at a point of time such as the present when it has been possible through paths of thought, first trod by the great German theoretical physicists, Planck and Einstein, to discover that certain of the fundamental viewpoints, on which physical research has been based for a long time, cannot be applied without radical changes to the study of the motion of particles in the interior of atoms. Where investigations of atomic problems just now are carried out with so great zeal, which in some respects has brought theoretical physics so strongly to the foreground, one repeatedly in theoretical investigations faces questions as to whether or not the assumptions employed conform to reality, and, as the work progresses, one is constantly compelled to carry out experimental investigations and let nature itself decide such questions of doubt. In recognition of the legitimate nature of these claims, the proposal to establish an institute met with general approval when it was made at the University where, as all such proposals, it was first dealt with in the Faculty of teachers of related subjects*, and I wish at once to express my thanks to the two representatives of the Faculty in the Konsistorium**, Professor Biilmann and Professor Johannsen, each of whom has from the first been helpful in many ways, both with the earlv formulation of the plans and with their accomplishment. But before the consideration of the matter was completed by Konsistorium, the University's board of highest instance, something happened which contributed essentially to the promotion of the matter, namely that a self-sacrificing interest in the establishment of the Institute was shown from private individuals. This happened in a, to me, very interesting and encouraging manner, in that my schoolmate and friend, Director Bevldme, who had heard about the submission of the proposal, approached Professor Faber, who at that time was Rektor of the University, and asked him if he thought that it would further the matter if means could be made available from private individuals to help accomplish the plans. When Professor Faber replied that he was convinced that that would be the case, a committee was formed with Director Berlime as treasurer and Director Harald Plum, Engineer N. M. Plum, Consul Hey, Banker Goldschmidt, Director Siegumfeldt, Professor Faber, Professor H$ffding, and the recently deceased Professor Troels Lund, as members; this committee took charge of a collection within a limited circle from which an amount of 80,000 kr. was raised. This result has not only been important as evidence of the self-sacrificing interest taken in a matter of such general nature, but it has been most directly useful to the establishment of the * [Le., the Faculty of Mathematics and Natural Sciences (det matematisk-naturvidenskabelige Fakultet).] ** [The governing board of the University.]

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Institute. In fact, this sum made it possible to make available to the University the very well situated plot, owned by the Municipality of Copenhagen, on which this building now stands. For the successful completion of the negotiations involved in the transfer of this property, and for the large amount of work he has done in this matter, the Institute owes a deep gratitude to Professor Faber. However, the sum that was made available by the collection mentioned was, of course, only a comparatively small beginning; for the kind interest that the matter received from Government and Parliament, which led to the appropriation of the means required for the construction and arrangement, I should like, on behalf of the Institute, to express our deep gratitude to the representatives present from the Government and the Legislature. [Bohr now expressed his thanks to the chief architect, Martin Borch, and to all the firms and artisans, by name, who had a part in the construction and arrangement of the Institute. He then continued :] While I speak of the arrangement of the Institute I cannot omit to mention the great help that Docent Dr. H . M . Hansen* has rendered me, not only with the planning and arrangement of the general features but in the thinking through of even the smallest details; and I should like to make use of this opportunity to give expression to the deep gratitude that so many of the devotees of physics in this country owe to Dr. Hansen because of his continual readiness to serve and his self-sacrificing interest in students as well as colleagues, a gratitude that we only rarely have occasion to express; at the same time I would like to express my pleasure over the fact that Dr. Hansen intends to take part in the scientific work in the now completed Institute, something that will be of the greatest value because of his exceptional knowledge of and insight into spectroscopic research. In fact, among the kinds of scientific work for which the Institute is arranged, spectroscopic research will occupy first place. This is closely connected with the circumstance that by the investigation of the light that matter can be brought to emit we have a means of the greatest value for obtaining information about the composition of matter and of the structure of the atoms of the various elements. Such investigations are made with instruments called spectrographs, and you will have occasion to see several types of these set up in the laboratory rooms. The type of spectrographs which in many cases are best adapted to refined investigations are the so-called grating spectrographs. It is therefore of great importance to us that the Board of Directors of the Carlsberg Foundation has made available to me a considerable sum of money for the construction and installation of a large grating spectrograph. The grating itself will be placed at the bottom of a 20-feet deep well dug in one of the laboratory rooms in the basement. Although we expect it at any moment, we have not yet received the grating itself, so today you will be able to see only the well construction. However, I should

*

[See Vol. 1, p. XXVII.]

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like to use the occasion to demonstrate to you, here in this room, the action of a grating; I shall do so by means of a number of small gratings, as the one I am holding here, which will be distributed to you in a moment. These small gratings are replicas on a film of collodion of a real grating which is made by ruling a huge number of fine parallel lines on a metal plate. The number of rulings is very large; on these gratings there are about 1000 rulings per mm. These small replica gratings can be used only for purposes of instruction, but in return they are very cheap. While a real large grating, useful for scientific purposes, costs several thousand kroner, the firm of Hilger in London, from which most of our optical equipment has been obtained, has delivered these small gratings to us for about one krone apiece. We have several dozens; however, not enough so that all of you can look through one at the same time. The action of a grating can be demonstrated simply by a couple of drawings. On this figure the horizontal lines represent a system of waves, corresponding to waves spreading on a surface or, in our case, to a system of light waves. Now, if these waves meet a screen in which there is a hole, the wave motion will propagate through the hole; but, if the hole is small compared to the distance between the waves, we shall get a system of spherical waves on the other side, as is shown in the lower part of the figure. If there were a slit instead of a hole, we should see the same, only the individual waves would not be spherical but cylindrical. If we now have not one slit but a large number of slits, the phenomenon is as simply shown on this other board. About each hole or slit is drawn a system of circles just like that on the former board. At first glance, the impression produced by such a figure is only one of confusion; however, if we look closely enough, certain regular features will appear from the mess. We see in particular that, down here where the circles are large, we obtain re-formed lines which correspond to the system of waves that we should have if the screen with the slit had not been there at all; but that is not the only system of waves formed by interference of the wave motions issuing from the individual slits. Here we see a row of lines which lie slantingly and form a system of waves which are propagated in a direction making an angle with the original waves, and here is one which slants to the other side; here again are waves which form a still larger angle with the original waves, and here some slanting the other way. Now, since the angles which the slanting wave systems make with the original system depend, besides on the distance between the slits, on the wavelength, i.e., the distance between consecutive wave surfaces in the original plane system of waves, or in the system of spherical waves issuing from each individual hole, such a grating provides a means of separating light into its different constituents, i.e., in its different colors, and a means which, for reasons which it would take too long to go into here, is far superior, e.g., to glass prisms. The understanding of the action of a grating is due to Fraunhofer who for many reasons may be regarded

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as the father of spectroscopy. The development of the grating as the chief instrument for optical research we owe to the American physicist Rowland. If we now look through such a small grating at a light source which, as this wire when it is made incandescent, emits light of all possible colors, we see first of all what corresponds to the reconstruction of the original wave surfaces in the previous figure; but in addition there occur wave systems which are bent to the sides, to a different extent for the different colors ; since the blue rays are bent least and the red most, we see a spectrum as that shown here. Farther out we see other spectra corresponding to wave systems that are bent still more, as shown in the previous figure; they are very weak, and we shall not consider them. However, if, instead of pointing the grating toward a light source such as an incandescent platinum wire, we had pointed it toward a (glass) tube containing a gas, then, when electrical discharges pass through the tube, we shall see something quite different. The light will not contain all colors now, but only a few colors, and the spectrum will therefore not consist of a broad band but only of a few separate lines, such as is indicated farther down in the figure. Now the small gratings will be distributed, but before we proceed further it will be best to lower the blinds. As we now send a current through the platinum wire, those who have a grating will partly see the wire just as in the absence of the grating, but they will also see the spectra on either side, the strong spectra of the first order and the weaker spectra of the second order still farther out to the sides. If I now send discharges through this tube, you will instead of the broad spectra see a number of lines as drawn in the figure. It is by investigating such lines that it has been possible to gain an insight into the laws holding for the motions of the particles in the atoms. For example, this tube contains a small amount of the rare gas, helium, and, in fact, the study of the helium spectrum has not only given extremely important information about the nature of the helium atom, but has even revealed to us certain general laws which we may hope will help us to understand the structure also of the atoms of other elements. By this little interruption of my account of the arrangement of the Institute, you have had occasion to become acquainted with some of the means available to us for teaching purposes. As I mentioned before in connection with grating spectrographs, the optical instruments required for scientific investigations are often very expensive, and it has been very difficult to make the appropriated funds suffice. In this connection, I must mention that it has been of the greatest importance for the procurement of our optical equipment that a large anonymous g$t ofl0,OOO kr. has been given to the Institute for this purpose; it has made it possible for us to obtain certain instruments of great value for research, instruments that we otherwise should have to miss. Because of the enormous rise in prices in the last years, it has been a very difficult time in which to procure

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equipment. In recognition of this fact, the authorities have doubled the original apparatus grant, which had been estimated on the basis of prices prevailing before the war. Nevertheless, it appeared for a long time that we should have insurmountable difficulties because of the deteriorating rate of exchange ; for, the price of the equipment ordered in England rose in proportion as the Danish krone fell. However, we were rescued from this difficulty by a magnanimous offer from Banker Torben Meyer, of the firm Bros. Trier, who offered to provide the English and other foreign currency that we needed for the procurement of apparatus at a cost corresponding to the rates of exchange prevailing before the war; this offer amounted to a gift to the Institute of many thousand kroner. However, in spite of all this generosity which has been extended to the Institute, both by the authorities and by private individuals, it has not been possible to acquire equipment which permits us to carry out investigations in all parts of the spectrum, each part of which, from the longest heat rays to the very shortest Rontgen rays, contribute to make possible a delving into the secrets of atomic structure; if it is to be possible for us to have available, in the not too distant future, all the means required to carry out all the various desirable investigations, the state or private individuals must provide additional help. However, there are other approaches to the investigation of atomic problems than those offered by the spectra of the elements. Those of you who had occasion last Thursday to attend Professor Franck’s lecture in Denmark’s Natural-scientific Society will have heard how this outstanding physicist and his co-workers have succeeded in opening up a new avenue for the exploration of atomic structure ; namely by investigating the effect of collisions between electrons and atoms. The Institute is very fortunate that, with means made available by some of the friends already mentioned, it has been possible to invite Professor Franck to come up here and acquaint us with the results of his important researches and help us with the arrangement of the Institute, and introduce us to the difficult experimental methods developed by him; you will find an apparatus used in such investigations set up in one of the adjacent laboratory rooms. However, we are indebted to Professor Franck not only for his present visit, which now unfortunately will soon be over, but for the fact that we can expect him back for another visit next autumn, and that is something to which all of us are looking forward with the greatest pleasure. In addition to research on ionization by collisions, there are several other fields of experimental research which are closely connected with the problem of atomic structure, above all the study of the so-called radioactive elements. In fact, all of you will know that the ingenious English natural scientist, Sir Ernest Rutherford,-who is among the greatest physicists of all time-has shown how it is possible from such studies to obtain direct information about the nature of

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the building stones of atoms. Many who are present here had occasion to hear Sir Ernest Rutherford himself tell about these investigations in the lectures he delivered at the University last September. It was hoped originally that this Laboratory might have been completed so early that the dedication could have taken place during Rutherford’s visit which, of course, would have been extremely felicitous. Because of delays we did not accomplish that but we are pleased to have with us another representative of the scientists who have occupied themselves thoroughly with radioactive researches, a man who himself has carried out very important investigations in this field, namely Professor Hevesy from Budapest. Professor Hevesy came to Copenhagen last spring, when we hardly could expect the Laboratory to be quite ready, but when, nevertheless, we hoped that the scientific work might begin here. In this case, the delay in the arrangement of the Laboratory has had a fortunate consequence for Danish science, in that Professor Hevesy found a temporary home with Professor Br$ndsted* in the physicalchemical laboratory at the Technical University. Together they have begun and carried oul some very important investigations that most of you undoubtedly have heard about on the separation of elements into components with identical chemical and physical properties but with different atomic weights. Although it is to be hoped that this successful collaboration with Professor Br4ndsted will continue, as it undoubtedly will, we are looking forward, now that the Institute is ready for scientific work, to profit from Professor Hevesy’s valuable participation in this work. It is with great pleasure that I, now at the dedication of the Institute, can invite to work here, besides the scientists already mentioned, a number of promising younger scientists, among whom are representatives from our neighboring countries. It is with the greatest pleasure that I bid the permanent personnel of the Institute welcome to the commencement of regular work and thank them for all the help with the arrangement of the Institute that each has rendered. I should like to emphasize in particular how happy we are by having, as the first scientific assistant connected with the Institute, the young Dutch physicist Dr.Kramers. Dr. Kramers has been in this country for the past 4i years, and during this time he has carried out a large amount of scientific research, in recognition of which, for one thing, he obtained the doctor’s degree at the University of Leiden two years ago. I have recognized his great ability from the time I got acquainted with him on his arrival in this country and, on behalf of the Institute, I should like to

*

[J. N. BrQridsted (1 879-1947), Danish physical chemist, professor at The Technicai University 190947. Known mainly for his many applications of thermodynamics to chemistry and important considerations on the foundations of thermodynamics.]

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express our pleasure in knowing that there is connected with it this able young man who not only is familiar with the methods and results of theoretical physics as few others but who himself has made important contributions to the elucidation of just those problems that we plan to give particular attention to here. In the last few years, Dr. Kramers has not only been a great help to me in my scientific work, but also in the instruction and guidance of students. This leads me to emphasize once more that this Institute is not intended solely for scientific research but is also to be a homestead for the teaching of physicists and others with special interest in physics, and I should like to make use of this opportunity to say that the combination of these tasks is a matter of the greatest significance as a portent of the successful growth of the Institute. In fact, it is in the nature of scientific researches that no one dares give definite promises for the future; we must be prepared that, on the road that at this moment is believed to lie open and smooth before us, obstacles can pile up which entirely bar the road, or to the overcoming of which entirely new ideas are required. It is therefore of the greatest significance not just to depend on the abilities and powers of a limited circle of researchers; but the task of having to introduce a constantly renewed number of younger people into the results and methods of science contributes in the highest degree to continually taking up questions for discussion from new sides; and, not least through the contributions of the young people themselves, new blood and new ideas are constantly introduced into the work. As I express the assurance that we shall do our utmost to merit the confidence shown 11s by the great generosity of state and individuals, I should like, as I close this account, to express the hope that this Institute may be a place where, in the course of time, many young devotees of physical science may obtain guidance in their study and help to make their own contribution to the advancement of our understanding of nature, and to the honor of Danish science.