SCIENTIFIC USE OF THE IMAGINATION. 151 



the question. Such arguments are absolutely valueless. 

 Without committing myself in the least to De la Rive's 

 notion, without offering any objection here to the doctrine 

 of spontaneous generation, without expressing any adhe- 

 rence to the germ theory of disease, I would simply draw 

 attention to the fact that in the atmosphere we have parti- 

 cles 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 Israel- 

 itish hyperbole regarding the sands upon the sea-shore. 



The varying judgments of men on these and other ques- 

 tions 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 impressions 

 made upon us by any circumstance, or combination of cir- 

 cumstances, depend upon our previous state. Two travellers 

 upon the same peak, 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 feelings are sure to differ which have two 

 such different antecedent states. In our scientific judg- 

 ments the law of relativity may also play an important part. 

 To two men, one educated in the school of the senses, who 

 has mainly occupied himself with observation, and the other 

 educated in the school of imagination as well, and exercised 

 in the conceptions of atoms and molecules, to which we 

 have so frequently referred, a bit of matter, say -^^th of 

 of an inch in diameter, will present itself differently. The 

 one descends to it from his molar heights, the other climbs 

 to it from his molecular low-lands. To the one it appears 

 small, to the other large. So also as regards the apprecia- 

 tion of the most minute forms of life revealed by the micro- 

 scope. To one of these men they naturally appear conter- 

 minous with the ultimate particles of matter, and he readily 



