124 FRAGMENTS OF SCIENCE. 



would not exhibit a stricter continuity. And Mr. 

 Grlaisher will inform you, that if our hypothetical shell 

 were lifted to twice the height of JVlont Blanc above 

 the earth's surface, we should still have the azure over- 

 head. Everywhere through the atmosphere those 

 sky-particles are strewn. They fill the Alpine valleys, 

 spreading like a delicate gauze in front of the slopes of 

 pine. They sometimes so swathe the peaks with light 

 as to abolish their definition. This year I have seen 

 the Weisshorn thus dissolved in opalescent air. By 

 proper instruments the glare thrown from the sky-par- 

 ticles against the retina may be quenched, and then the 

 mountain which it obliterated starts into sudden de- 

 finition. l Its extinction in front of a dark mountain 

 resembles exactly the withdrawal of a veil. It is 

 then the light taking possession of the eye, not the 

 particles acting as opaque bodies, that interferes with 

 the definition. By day this light quenches- the stars ; 

 even by moonlight it is able to exclude from vision all 

 stars between the fifth and the eleventh magnitude. It 

 may be likened to a noise, and the feebler stellar radi- 

 ance to a whisper drowned by the noise. 



What is the nature of the particles which shed this 

 light ? The celebrated De la Kive ascribes the haze of 

 the Alps in fine weather to floating organic germs. 

 Now the possible existence of germs in such profusion 

 has been held up as an absurdity. It has been affirmed 

 that they would darken the air, and on the assumed 

 impossibility of their existence in the requisite numbers, 

 without invasion of the solar light, an apparently 

 powerful argument has been based by believers in 

 spontaneous generation. Similar arguments have been 

 used by the opponents of the germ theory of epidemic 

 disease, who have triumphantly challenged an appeal to 

 1 See the ' Sky of the Alps, 1 Art. iv. sec. 3, vol. i. 



