( 300 ) 

 NOTES AND CORRESPONDENCE. 



Reply to some Remarks by F. H. Wenham. — In an article by 



F. H. Wenham, Esq., of London, published in the 'Quar- 

 terly Journal of Microscopical Science' for July, 1854, I have 

 noticed the following paragraph : — 



"These experiments [made by Mr. Wenham] will readily 

 account for the difficulty of discovering the markings or struc- 

 ture of a severe test when mounted in balsam ; for as thus 

 seen it may be inferred that no aperture exceeding 85° can 

 be made to bear upon it, and this is even supposing that the 

 largest aperture object-glass that has ever been constructed is 

 used. Such being the case I am somewhat puzzled at an 

 announcement that appears to contradict this fact, coming 

 from one that must be considered as authority in these 

 matters. I refer to Professor Bailey, who, in a letter addressed 

 to Matthew Marshall, Esq., dated January 20, 1852, first 

 speaks of an American object-glass of very large aperture 

 (172i°), and its performance on the most difficult tests known, 

 and then proceeds to say, 'In all these cases (and in fact 

 whenever I allude to a test-object) I mean the halsam-monnteA 

 specimens. The dry shells 1 never use as tests.' Tliis asser- 

 tion seems to me to be extraordinary, and very like saying 

 that an aperture of 85° or 90° will do everything that is re- 

 quired. I have invariably found that when very difficult tests 

 are mounted in balsam I cannot discover the markings, and 

 certainly the reasons herein given will account for it. It is 

 to be hoped that the American opticians have discovered 

 some new and peculiar principle in object-glasses, that will 

 render a smaller amount of aperture serviceable ; but however 

 this may be, I think that Professor Bailey's statement requires 

 some explanation." — Journ. Mic. Science, July, 1854, p. 215. 



It is apparent from the above that Mr. Wenham has con- 

 vinced himself, both by " reasons" and experiment, that I 

 ought not to have seen the markings on delicate test-objects 

 when mounted in balsam ; and that as he invariably found 

 tliat he could not discover these markings, therefore some 

 new and peculiar principle in object-glasses must have been 

 discovered to account for the success of American opticians. 

 In answer to this I would state that both in print, as well as 

 in private letters, I stand fully committed to the statement 

 that I can resolve the most difficult tests known even when 

 mounted in balsam. In 1849 I stated in this Journal, vol. vii., 

 p. 268, that " the resolution of these tests mounted dry is so 



