SUPPLEMENT. 369 



By way of illustrating these "little differences," it may be 

 mentioned that among first- class objectives of the same mag- 

 nification, aperture and resolving power, greater and lesser 

 working distance will be found, and right here is the solution 

 of the dogma of (bo-called) penetration, for, of the glasses above 

 mentioned, that one having the greater working distance will 

 be endowed with the greater penetration. This is the whole 

 thing in a nutshell, as set forth by the writer years ago. 



If, in the comparison of two objectives, alike in magnification, 

 aperture and resolving power, one shall be found to have the 

 longer working distance, then is its superiority demonstrated, 

 and, be it remembered, that comparisons of objectives ought 

 always to be made in this kind of a way, otherwise any attempt 

 at comparison would be as futile as if we were to compare a tur- 

 nip with an orange. 



Again, ij it can be shown that a medium power glass, say a 

 l-6th or a 1-lOth having the widest aperture known, and also com- 

 paratively large working distance, say l-50th of an inch, will 

 more than do any work that can be done with objectives of ex- 

 ceedingly high power, and correspondingly short working dis- 

 tance [excess of aperture being barred by the above named 

 conditions), it will be obvious that the former will be eminently 

 the superior glass. 



Now the facts warrant the assertion that just such one-sixth 

 and one-tenth are made, and by American opticians. The 

 writer has had, and still has in his possession just such glasses. 

 His first contribution to the columns of the News, four years 

 since, set forth their claims, and he has never had occasion to 

 make either modification or retraction of his original statement. 

 When such occasion shall occur, the readers, of this journal will 

 be promptly advised ; until then I claim (especially for the one- 

 sixth) unequaled intensity of definition, widest known aperture, 

 combined with large working distance in other words, without 

 that sacrifice of " working distance" alluded to by Mr. 

 Gundlach. 



I embrace this, my first opportunity, to say that I have lately 

 examined at length a new duplex one-tenth, the work of a 

 young American optician. This new one-tenth is similar in 



24 Microscopy. 



