SCIENTIFIC USE OF THE IMAGINATION. 123 



earth's surface, we should still have the azure overhead. 

 By day this light quenches the stars ; even by moon- 

 light 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 num- 

 bers, 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 the microscope and the chemist's balance to decide 

 the question. Such arguments, however, are founded 

 on a defective acquaintance with the powers and pro- 

 perties of matter. Without committing myself in the 

 least to De la Rive's notion, to the doctrine of spon- 

 taneous generation, or to the germ theory of disease, 

 I would simply draw attention to the demonstrable 

 fact, that, in the atmosphere, we have particles which 

 defy both the microscope and the balance, which do 

 not darken the air, and which exist, nevertheless, in 

 multitudes sufficient to reduce to insignificance the 

 Israelitish hyperbole regarding the sands upon the sea- 

 shore. 



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 impor- 

 38 



