38 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



tion appears to exist in a constant relation to the density of 

 the zodiacal light ; or, in other words, that its light is a screen, 

 which, by its relative opacity, arrests a portion of the heat 

 emitted by the sun. This fact is, he says, placed beyond a 

 doubt by a long series of thermometrical observations com- 

 pared with the observations of the density of the zodiacal 

 light. 3 B, September 7, 1871, 524. 



BLUE COLOR OF LAKE WATEK. 



We have already made some reference to the observations 

 of Professor Tyndall in regard to the cause of the blue color 

 of the Lake of Geneva, and to his ascribing it to the presence 

 of solid particles of extreme fineness suspended in the water. 

 The researches of Professor Tyndall, and of Professor Loret 

 on the same subject, have been reproduced by Professor De- 

 lafontaine, of Chicago, and lately presented before the Acad- 

 emy of Sciences of that city. As the result of his observa- 

 tions, he stated that common water, when crossed by a beam 

 of light, becomes illuminated, and assumes a blue color, polar- 

 izing the light in the same w T ay that air does, and that it loses 

 this property on having undergone a complete purification by 

 the removal of solid matter suspended in the liquid. His ex- 

 periments were tried upon the Chicago River water in its 

 natural state, which exhibited great illuminating power even 

 after a rest of several weeks. By first filtering and then care- 

 fully distilling the same water, w T ith the aid of permanganate 

 of potash, for the purpose of removing the organic matter, he 

 found that it lost almost the whole of its power of illumina- 

 tion. Chicago Times, December 14,1870. 



PHYSICAL ATLAS OF FRANCE. 



An important work has just been commenced in France, 

 under the direction of Messrs. Delaunay and Marie Davy, 

 with the title of" Physical Atlas of France," a specimen num- 

 ber having been issued by these gentlemen for the criticism 

 of their friends and correspondents. The scale on which most 

 of the maps are to be executed is two millionths of an inch, 

 which is thought to be sufficiently large to allow a represen- 

 tation of the different elements to be included. The subjects 

 treated of in this atlas will be classified under six different 

 heads : first, the political administrative condition of France, 



