350 ANNUAL OF SCIENTIFIC DISCOVERT. 



Boussingault, during the winter of 1841-2, found that a thermom- 

 eter plunged in snow to the depth of a decimeter (about 4 inches) 

 sometimes marked 9° of heat greater than at the surface. 



Meteoric Theory. — Sir John Herschel has recently advanced the 

 theory, not wholly new, but never before supported by well-known 

 facts, that meteoric showers are simply the light caused by the 

 collision of the earth's atmosphere with the tenuous substance of 

 a comet. Prof, Adams, who shared with Leverrier the credit of 

 discovering the planet Neptune, accepts this theory. Those who 

 have read Prof. Tyndall's work on heat may find in this theory an 

 additional reason to accept the learned writer's hj'pothesis as to 

 the orio;in of the sun's light and heat. 



Color of the Clouds. — The varied colors which the clouds assume 

 at various times, especially at sunrise and sunset, are explained 

 on the principle that the clear, transparent vapor of water absorbs 

 more of the red rays of light than of any other, while the lower 

 strata of the atmosphere offer more resistance to the passage of 

 the blue rays. At sunrise and sunset the light of the sun has to 

 pass though about 200 miles of atmosphere within a mile of the 

 surface of the earth in order to illuminate a cloud a mile from the 

 ground. In passing through this great thickness the jjlue rays are 

 absorbed to a far greater extent than the red, and much of the 

 yellow is also removed. Hence clouds thus illuminated are red. 

 When the sun is higher above the horizon, the yellow light passes 

 more readily, and the clouds become orange, then yellow, and 

 finally white. Clouds in different parts of the sky, or at different 

 elevations, often sliow these various colors at the same time. 



Determining the Colors of the Stars. — To the astronomer this is 

 a subject of much interest, and different observers vary greatl}' in 

 their opinions, in this respect, as to particular stars. For the sake 

 of a more definite and reliable means of determination, a simple 

 contrivance has been recently invented, consisting of a series of 

 vials filled with solutions of known tints, and attached to a re- 

 volving drum. A platinum wire is rendered incandescent by means 

 of a galvanic battery, and as the vials are brought before the light 

 their colors can be distinctly seen at night, and by successive com- 

 parisons with that of the star the exact shade is found. 



