434 FRAGMENTS OF SCIENCK. 
stricter continuity. And Mr. Glaisher will inform you, 
that if our hypothetical shell were lifted to twice the 
height of Mont Blanc above the earth's surface, we should 
still have the azure overhead. 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 radiance 
to a whisper drowned by the noise. 
What is the 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, 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 chal- 
lenged an appeal to the microscope and the chemist's balance 
to decide the question. Such arguments, however, are 
founded on a defective acquaintance with the powers and 
properties of matter. Without committing myself in the 
least to De la Hive's notion, to the doctrine of spontaneous 
generation, or to the germ theory of disease, I would 
simply draw attention to the demonstrable fact, that, in 
the atmosphere here, we have particles which defy both the 
microscope and the balance, which do not darken the air, 
and which exist, nevertheless, in multitude sufficient to re- 
duce to insignificance the Israelitish hyperbole regarding 
the sands upon the seashore. 
The varying judgments of men on these and other 
questions may perhaps be, to some extent, accounted for 
by that doctrine of Relativity which plays so important a 
part in philosophy. This doctrine affirms that the impres- 
sions made upon us by any circumstance, or combination 
of circumstances, depend upon our previous state. Two 
travelers upon the same height, the one having ascended 
to it from the plain, the other having descended to it from 
a higher elevation, will be differently affected by the scene 
around them. To the one nature is expanding, to the 
other it is contracting, and impressions which have two 
