"202 A. A. MERLIN ON CRITICAL EMPLOYMENT OF THE MICROSCOPE. 



and medium magnifications, are readily attainable, the most 

 massive and rigid stands of the Powell No. 1 type, and apo- 

 chromatic objectives, being only absolutely necessary in the most 

 difficult branches of research, and when the best attainable 

 photomicrographs are in question. 



Now we come to the fourth point, and have to consider the 

 opponents of large-cone critical images on theoretical grounds, 

 i.e., those who think with Abbe that central illumination with 

 a narrow incident pencil, the perfectly logical corollary drawn 

 by him from his diffraction theory of microscopical vision, is 

 the necessary condition for the attainment of an image strictly 

 similar to the object, or at least the nearest possible approach 

 thereto capable of being afforded by the objective employed. 

 Now there is one infallible proof to which all theories, however 

 profound or ingenious they may be, or however much we may 

 admire the labours of their authors, have always, sooner or 

 later, to submit, and by which they must inevitably stand or 

 fall : and that is, observed fact. When a new and brilliant 

 theory on any philosophical subject is first promulgated by some 

 eminent scientist, it is the tendency of self-elected disciples, 

 exponents, and admirers to permit themselves to be carried 

 away by their enthusiasm, and to go to lengths in defending 

 and expounding the new tenets that their author would be 

 perhaps the first to deprecate. Forgetting the lessons of the 

 past, that few indeed are the theories which have withstood 

 the test of time unscathed, they from the outset regard matters 

 not from a strictly impartial, but from a purely partisan 

 standpoint, and, while eagerly calling attention to and exagger- 

 ating the significance of such observations as may appear to 

 them at the moment to favour their views, they, on the other 

 hand, heatedly call in question and throw doubt upon those 

 which tend to the contrary, often without patient inquiry or 

 experiment. It has been said that even a bad theory is better 

 than none at all, and this is undoubtedly true in so far as it 

 paves the way for that calm, philosophical discussion from which 

 we may hope to eventually attain some nearer approach to the 

 truth, as distinct from controversy and personal recrimination, 

 which can only serve to retard progress. 



The object of the following remarks is not to discuss the 

 truth of the diffraction theory, except in so far as its doctrines 



