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New method of road building
Dec., 1880.]
Book Notices.
419
Sun Spots in 1879.--Wolf has compared the solar observations at Zurich, Palermo, Rome, Moncalieri, Athens, Madrid, Leipzig, Peckeliih and Washington, obtaining for the epoch of ininimum 1878"9. The variations in m~tgnetic declination at Milan, Vienna, Prague, Munich and Christiania indic tte the minimum epoch ]878"5. Both results agree in pointing to an epoch of 11"7 years.~Compt. Read. C. New Method of Road Building.--Oppermann proposes to build highways in two layers: 1, a bed of 15 to 20 centimetreu (5"9 to 7"87 inches) of coarse betou with hydraulic mortar; 2, a bed of smaller beton, cemented with a mixture of lime and one-half part of Portland or Boulogne cenlent and one-half part of slag. The stones in this second bed should be chosen exclusively from the hardest and most flinty varieties.--Chro~. Indust. C. N e w : E x p e r i m e n t u p o n S p e c t r a l R a y s . - L. Thollon has erected an apparatus for spectroscopic observations upon the hill of the Nice Observatory. He ha~ especially studied a group of four rays situated Jn the orange, two of which belong to iron and two are telluric. When the rays arc received fi'om the centre of the disc th~ telluric rays are nearly equl-distant from the iron ray's; but if the rays are taken from the eastern or western side of the disc the iron rays are displaced while the tclluric rays remain invariable. It is thus possible to demonstrate Freau's fornmla tbr light, as well as for sound, and daily to submit one of the most important laws of physical astronomy to carefhl verification.--Comptes Rendus. C.
Book
Notices.
POTABLE WATER.--How to form a Judgment on the Suitableness of Water ibr Drinking Purposes. By Charles Ekin, F. C.S. 12too.. J. & A. Churchill. London. ]880. This little book is addressed to those who practise sanitary water analysis in the hope of doing something toward extricating this important subject out of the unfortunate entanglements in which it has of late years become involved. When chemists of the highest reputatlon mutually denounce each other's methods of an'dysis, and each regards the one he himself has invented as " the only trustworthy process in existence ;" and when chemists of these several cliques di~i~r so widely in their certified opinions, that samples of the very same
Book Notices.
419
Sun Spots in 1879.--Wolf has compared the solar observations at Zurich, Palermo, Rome, Moncalieri, Athens, Madrid, Leipzig, Peckeliih and Washington, obtaining for the epoch of ininimum 1878"9. The variations in m~tgnetic declination at Milan, Vienna, Prague, Munich and Christiania indic tte the minimum epoch ]878"5. Both results agree in pointing to an epoch of 11"7 years.~Compt. Read. C. New Method of Road Building.--Oppermann proposes to build highways in two layers: 1, a bed of 15 to 20 centimetreu (5"9 to 7"87 inches) of coarse betou with hydraulic mortar; 2, a bed of smaller beton, cemented with a mixture of lime and one-half part of Portland or Boulogne cenlent and one-half part of slag. The stones in this second bed should be chosen exclusively from the hardest and most flinty varieties.--Chro~. Indust. C. N e w : E x p e r i m e n t u p o n S p e c t r a l R a y s . - L. Thollon has erected an apparatus for spectroscopic observations upon the hill of the Nice Observatory. He ha~ especially studied a group of four rays situated Jn the orange, two of which belong to iron and two are telluric. When the rays arc received fi'om the centre of the disc th~ telluric rays are nearly equl-distant from the iron ray's; but if the rays are taken from the eastern or western side of the disc the iron rays are displaced while the tclluric rays remain invariable. It is thus possible to demonstrate Freau's fornmla tbr light, as well as for sound, and daily to submit one of the most important laws of physical astronomy to carefhl verification.--Comptes Rendus. C.
Book
Notices.
POTABLE WATER.--How to form a Judgment on the Suitableness of Water ibr Drinking Purposes. By Charles Ekin, F. C.S. 12too.. J. & A. Churchill. London. ]880. This little book is addressed to those who practise sanitary water analysis in the hope of doing something toward extricating this important subject out of the unfortunate entanglements in which it has of late years become involved. When chemists of the highest reputatlon mutually denounce each other's methods of an'dysis, and each regards the one he himself has invented as " the only trustworthy process in existence ;" and when chemists of these several cliques di~i~r so widely in their certified opinions, that samples of the very same