126 Noherfs Nineteenth Band 



I do not know by wliat authority Dr. W. says that I have 

 made such a claim for Tolles' lenses ; I have never puhhshed any 

 such claim ; when I do I shall refer to Dr. Woodward's own reports 

 for evidence of the propriety of it ; e. g. in the ' Am. Jour. Sci.' * he 

 gives the results of his trials of various objectives of different powers, 

 from |th to sVth, and by various makers. No one could resolve 

 the test-plate finer than the 15th band. This statement he repeats 

 in the ' Quar. Jour. Mic. Sci.' for October, 1868.t In the ' Monthly 

 Mic. Jour. 'I he gives the following, additional : — " The \i\x of Wales 

 and ^Vth and sVth of Powell and Lealand, all dry lenses, resolved 

 the 15th band, and not the 16th. An immersion ^^th by Wales 

 resolved the iVth band, and failed to go farther. An immersion 

 ^Vth by Wales resolved the 17th band, but failed to go farther. A 

 Hartnack, No. 11, also resolved the 17th band, and failed to go 

 farther. A Tolles' immersion ^th, recently constructed for Dr. J. 

 C. Kives, of this city, resolved the 14th band." " A Tolles' immer- 

 sion Toth:§ with this I was unable to see beyond the 16th band." 

 Dr. W. has broached this subject — not I. I now ask Dr. W. to 

 name the "few cases," or any one case, in which the lenses of 

 English or any other makers have excelled the performance of those 

 two. Did he ever see, read of, or hear of any ith or ^th objective 

 of any other maker that had excelled what those did in his own 

 hands ? I ask him to reply without equivocation — yes or no — as 

 publicly as he has provoked the inquiry. 



Dr. Woodward takes pains to say, "Mr. Stodder's complaint 

 that his paper in the ' American Naturalist ' has been ignored, 

 certainly cannot apply to me." Dr. W. has made the application 

 himself; I did not have him in my mind when writing that pas- 



* Vol. xlvi., p. 353, Nov., 1868. f P. 229. J Vol. ii., p. 292. 



§ Dr. Woodward and Mr. W. S. Sulivant both say that the ^th objective referred 

 to is only an eighth, " English standard." The instrument has since been measured 

 by two parties, one made it a full xuth, the other a little less. The English 

 standard and the American are the same, viz. the English inch. The mistake of 

 those gentlemen was that they took for granted that their Enghsh objectives must 

 he right. On this point I will copy from Dr. W. B. Carpenter, as I suppose that 

 everyone has not read his book : " It may be well here to remark, that the desig- 

 nations given by opticians to their objectives are often far from representing their 

 real focal length, as estimated by that of single lenses of equivalent magnifying 

 power ; a temptation to underrate them being afforded by the consideration, that if 

 an objective of a certain focus will show a test-object as well as another of higher 

 focus, the former is to be preferred. Thus it happens that what are sold as half- 

 inch objectives are often more nearly y%ths ; and that what are sold as ^ths are not 

 unfrequently more nearly iths " (' The Microscope." London. 4th ed., p. 184). 



This quotation shows the practice and explains the reason for it. See also 

 ' Quar. Journ. Mic. Science,' 18G2 and 18G3 ; Mr. E. Bicknell in ' Am. Naturalist,' 

 1870 ; and Mr. Cross in ' Journ. Franklin Institute,' Philadelphia, 1870, and repub- 

 lished in ' Monthly Mic. Journ.,' Sept., 1870. 



I am happy to say that at the recent meeting of the American Association for 

 tlic Advancement of Science, held at Troy, New York, a committee was appointed 

 by the suggestion of Dr. Josiah Curtis, of Boston, to consider this subject, and to 

 secure, if possible, uniformity of designation at least for American objectives. 



