150 FRAGMENTS OF SCIENTI-. 



the summit of Mont Blanc the blue is as uniform and co 

 herent as if it formed the surface of the most close-grained 

 solid. A marble dome would not exhibit a stricter con 

 tinuity. And Mr. Glaisher will inform you that if our hy 

 pothetical shell were lifted to twice the height of Mont 

 Bkinc above the earth s surface, we should still have the 

 azure overhead. 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 

 &quot;Weisshorn thus dissolved in opalescent air. By proper 

 instruments the glare thrown from the sky-particles against 

 the retina may be quenched, and then the mountain which 

 it obliterated starts into sudden definition. Its extinction 

 in front of a dark mountain resembles exactly the with 

 drawal of a veil. It is the light then taking possession of 

 the eye, and 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 magni 

 tude. It may be likened to a noise, and the stellar radiance 

 I-) a whisper drowned by the noise. 



What is th^ nature of the particles which shed this 

 light ? The celebrated De la Rive 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, a powerful argument has been based by be 

 lievers in spontaneous generation. Similar arguments 

 have been used by the opponents of the germ theory of 

 epidemic disease, who have triumphantly challeged an ap 

 peal to the microscope and the chemist s balance to decide 



