1892.] NEW-YORK MICROSCOPICAL SOCIETY. 27 



general concurrence in the belief that the final unit of all ma- 

 terial things had been reached. You may be sure there would 

 still be a goodly number of men endowed with that high order 

 of inquisitiveness which finds its full satisfaction in merely solv- 

 ing problems, and who would persist in peering and prying, d eter- 

 mined to find something beyond the so-called end. 



Of this class are the men who have worked away at the 

 diatom-markings, through good report and evil report, encour- 

 aged and sustained by an abiding faith in the intrinsic value of 

 pure truth. To one unfamiliar with microscopical science the 

 length of time and amount of labor, on the part of both the 

 worker with and the constructor of lenses, which were required 

 to accomplish the progress in mere technical achievement 

 which I have briefly described, must be a matter of profound 

 surprise and wonder; and even after one has in a measure 

 realized that many years of patient and persistent effort were 

 consumed in getting over the ground between merely seeing 

 plain lines the 50,000th of an inch apart, and breaking those 

 lines up into visible dots having a distance of the 50,000th of an 

 inch between their centres (which is in most cases the equivalent 

 of resolving lines the ioo,oooth of an inch apart), he may still 

 be unable to appreciate the importance of the accomplishment or 

 to believe that the result could warrant the necessary expenditure 

 of energy. But the pursuit of knowledge for the sole sake of 

 knowledge has been justified'over and over again by the discovery 

 that what was sought with entirely disinterested motive and with 

 no utilitarian aim, has proved to be a precious boon and blessing to 

 all mankind. And so the enthusiasts who used to spend their 

 time " fighting objectives," and who braved the jeers of their 

 more practical brethren, have now the satisfaction of knowing 

 that their exacting demands for improved apparatus with which 

 to resolve more and more difficult tests, have been the incentive 

 under which the opticians have produced lenses of wider and 

 wider angle of aperture, with better and better correction of 

 aberrations. The result has been, first, the working out of the 

 very ingenious homogeneous immersion principle and, more 

 lately, of the wonderfully delicate apochromatic combination, in 

 the application of which to the microscope objective a revolu- 

 tionary theory in optics has been developed, while, at the same 



