SCIENTIFIC USE OF THE IMAGINATION 



- Small in mass, the vastness in point of 

 number of the particles of our sky may be 

 inferred from the continuity of its light. 

 It is not in broken patches, nor at scat- 

 tered points, that the heavenly azure is 

 revealed. To the observer on the 

 summit of Mont Blanc, the blue is as 

 uniform and coherent as if it formed the 

 surface of the most close-grained solid. 

 A marble dome would not exhibit a 

 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 argu- 

 ments 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 properties 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 suffi- 



cient 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 im- 

 portant a part in philosophy. This doc- 

 trine affirms that the impressions made 

 upon us by any circumstance, or com- 

 bination of circumstances, depend upon 

 our previous state. Two travellers 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 such 

 different antecedent states are sure to 

 differ. In our scientific judgments the 

 law of relativity may also play an impor- 

 tant part. To two men, one educated 

 in the school of the senses, having mainly 

 occupied himself with observation ; the 

 other educated in the school of imagina- 

 tion as well, and exercised in the con- 

 ceptions of atoms and molecules to which 

 we have so frequently referred, a bit of 

 matter, say srrHsth of an inch in dia- 

 meter, will present itself differently. The 

 one descends to it from his molar heights, 

 the other climbs to it from his molecular 

 lowlands. To the one it appears small, 

 to the other large. So, also, as regards 

 the appreciation of the most minute 

 forms of life revealed by the microscope. 

 To one of the men these naturally appear 

 conterminous with the ultimate particles 

 of matter; there is but a step from 

 the atom to the organism. The other 

 discerns numberless organic gradations 

 between both. Compared with his atoms, 

 the smallest vibrios and bacteria of the 

 microscopic field are as behemoth and 

 leviathan. The law of relativity may to 

 some extent explain the different atti- 

 tudes of two such persons with regard to 

 the question of spontaneous generation. 

 An amount of evidence which satisfies 

 the one entirely fails to satisfy the other ; 



