Cooper Hewitt interrupter as an aid in wireless telegraphy

April, t9o3. ]

Notes and Comments.

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Notes and Comments. C O O P E R H E W I T T I N T E R R U P T E R AS AN AID IN W I R E L E S S TELEGRAPHY. E a c h advance in wireless telegraphy has emphasized t h e inefficiency of the spark-gap i n t e r r u p t e r , and this element has t h r e a t e n e d to be t h e weak factor in the commercial d e v e l o p m e n t of aerial transmission. I n t h e Marconi transatlantic e x p e r i m e n t s t h e power required at t h e disruptive gap was enormous in comparison with t h e presumable q u a n t i t y of energy radiated from t h e a n t e ~ _ ~ , and a ~erious i n c i d e n t of the great local disturbance t h e r e b y set up has been t h e adverse effect on telephonic service over a wide range, w h i c h forecast t r o u b l e for the exploiters of commercial wireless telegraphy. I t is, therefore, a m a t t e r of unusual interest to learn t h a t an i n t e r r u p t e r for an oscillating circuit has recently been devised w h i c h n o t only very greatly reduces t h e draft on t h e source of electrical energy b u t possesses most valuable properties with respect to exact control, a n d at the same time is e x t r e m e l y simple in form and application. I n wireless telegraphy t h e spark-gap oscillating circuit has heretofore been employed, either in connection with t h e simple induction coil or the disruptive gap I n his studies on t h e mercury vapor tube, it occurred to Mr. Peter Cooper Hewitt t h a t the " e l e c t r i c v a l v e " property of t h e vapor tube, w h i c h h e has employed in his static converter, could be applied to t h e oscillating circuit. This application h e has succeeded in carrying out in a most successful manner. Briefly stated, t h e spark-gap of t h e oscillating circuit is replaced by a mercury vapor tube in parallel with a condenser. A s s u m i n g t h a t t h e immediate source of electrical energy is a transformer, in t h e transformer secondary in series are a condenser a n d t h e p r i m a r y of the a n t e n n m - g r o u n d circuit, t h e condenser b e i n g s h u n t e d by a vapor tube. T h e tube does not differ in principle from the usual Cooper H e w i t t vapor tube, t h o u g h naturally of a somewhat different form, owing to its different application, and t h e nature of t h e work to b e performed. T h e transformer secondary voltage m a y range between Io, co'o a n d 2o,oco volts. T h e f u n d a m e n t a l advantage of this i n t e r r u p t e r is t h e enormous speed of i n t e r r u p t i o n t h a t m a y be attained, a n d t h e absolute control of this speed. Moreover, b y proper design a n d adjustment, any given rate of a d j u s t m e n t can be secured. W i t h the disruptive spark t h e r e is a limit to t h e efficient rate of i n t e r r u p t i o n fixed by the time required for the condenser to clear itself, a n d this rate, as well as t h e total effect, is variable, owing to t h e mobility of t h e arc, t h e condition of the k n o b s with respect to polish, etc. This latter consideration does not apply to t h e mercury electrode surface, a n d t h e vacuum discharge is not subject to similar fluctuations. It follows t h a t with this new type of i n t e r r u p t e r it is possible to create a n d m a i n t a i n continuously oscillations of an absolutely definite character, the great importance of w h i c h consideration with respect to wireless telegraphy is obvious. T h e practical advautages of the i n t e r r u p t e r are no less evident. T h e efficiency is very high, t h e loss being about proportional to t h e drop of about

3 I6

Book Notices ."

[J. 17. I.,

14 volts in t h e tube, and in a circuit of ro,ooo volts this a m o u n t s to b u t a small fraction of I per cent. T h e device, consisting merely of a glass tube or bulb with sealed-in electrodes, is inexpensive, a n d in case of breakage can be immediately replaced b y a n o t h e r in the same m a n n e r as an incandescent

lamp.--Electrical World. W I R E L E S S T E L E G R A P H Y AND T H E " S T . L O U I S . " The painful u n c e r t a i n t y a t t e n d i n g t h e belated " S t . Louis," of w h i c h n o t h i n g was beard, from the time she left Cherbourg until she was sighted at Nantucket, a week overdue, suggests t h a t for passenger ships at least, t h e time will be welcomed w h e n every vessel is equipped with a wireless teleg r a p h ,,,~,,t. A l t h o u g h n o n e of t h e vessels so equipped would be capable of repeating Marconi's feat w h e n h e communicated from one of t h e vessels of t h e A m e r i c a n Line over 1,5oo miles at sea with t h e powerful Poldhu station, a r a n g e of say 200 miles should be quite within commercial practicability. Considering the crowded condition of t h e various steamship lanes across t h e Atlantic, it would be impossible, were all passenger ships so provided, for a vessel to r e m a i n u n s p o k e n for more t h a n a day or two at t h e longest ; and a liner disabled in mid-Atlantic should be able to c o m m u n i c a t e from ship to ship with h e r h o m e port a n d news of h e r trouble be made known, l o n g before t h e day set for h e r arrival. I n this way a n enormous a m o u n t of a n x i e t y could be spared to relatives a n d friends on t h e all-too-frequent occasions w h e n transatlantic vessels are disabled. Indeed, we consider t h a t just as soon as wireless telegraphy has b e e n placed on a t h o r o u g h commercial basis, it would be quite within reason for a law to be passed requiring all ships to install some one of the wireless telegraph systems w h i c h will be on t h e m a r k e t . - -

Scientific American.

Book Notices. The Alaska Frontier.

By Thomas Willing Balch, A.B. (Harvard), m e m b e r of t h e Philadelphia Bar. P h i l a d e l p h i a : Allen, Lane & Scott ; large 8vo, pp. 2~2. This book is an exhaustive study of t h e Alaska b o u n d a r y question, about which Mr. Balch published a paper, " T h e Alasko-Canadian F r o n t i e r , " in t h e Journal oflhe Franklin fnslitute for March, I9o2. To collect his information Mr. Balch traveled as far west as Alaska and as far east as St. Petersburg. This book gives a complete account up to 19o3 of all t h e facts r e l a t i n g t o ' t h e b o u n d a r y question, i n c l u d i n g t h e negotiations t h a t preceded the AngloMuscovite Treaty of 1825 ; t h e subsequent official acts of t h e various interested Governments, such as the t u r n i n g back by Russian officials in 1834 of t h e British brig " D r y a d ; " t h e events leading up to t h e purchase of Alask~ b y the United States, i n c l u d i n g a letter on t h a t subject by Frederick W.- Seward, the son of Secretary Sewar d ; t h e I n t e r n a t i o n a l Law governing t h e case ; and reproductions of twenty-eight maps, some of t h e m very rare. T h e a u t h o r proves conclusively t h a t up to t h e present time the Canadians h a v e not advanced in support of t h e i r contentions a n y t h i n g but " a nebulous maze of