NOTES AND CORRESPONDENCE. 



Limits of the Power of the Microscope. — On points of con- 

 troversy I will not here enter, but 1 may say that 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 believers in spontaneous genera- 

 tion. Similar arguments have been used by the opponents 

 of the germ theory of ej^idemic disease, and both parties 

 have triumphantly challenged an appeal to the microscope 

 and the chemist's balance to decide the question. Without 

 committing myself in the least to De la Rive's notion, with- 

 out offering any objection here to the doctrine of spontaneous 

 generation, without expressing any adherence to the germ 

 theory of disease, I would simply draAV attention to the 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, neveriheless, in mulliiudes sufficient to 

 reduce to insignificance the Israelitish hyperbole regarding 

 the sands upon the seashore. 



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 circum- 

 stances, depends 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 eleva- 

 tion, 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 judgments 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 



