1880.] 



MICROSCOPICAL JOURNAL. 



229 



placed "behind the objective, and 

 as near thereto as practicable." 



For this improvement in the 

 mechanical construction of the in- 

 strument, and for any advantage 

 that may result from placing the 

 second pair of reflecting prisms be- 

 low the eye -pieces instead of above 

 them, I am quite ready to accord 

 full credit to Mr. Stephenson ; 

 but it is quite clear from the facts 

 recorded in this paper that, with 

 these exceptions, the whole credit 

 of the optica] part of his " erecting 

 binocular" belongs to Riddell. I 

 do not, of course, accuse Mr. 

 Stephenson of intentional wrong in 

 arrogating to himself the merit that 

 really belongs to the American mi- 

 croscopist w^ho so long anticipated 

 him ; but it has been his misfortune 

 to forget, or not to have become 

 acquainted with, the widely pub- 

 lished work of his predecessor ; and 

 it has become my duty to vindicate 

 the truth of history, as I have done 

 in these pages. I do not doubt 

 that Mr. Stephenson, after taking 

 the trouble to read Riddell's papers 

 as reprinted so many years ago in 

 the Quarterly Journal of Mtcros- 

 copical Science, will hasten to ac- 

 cord full credit to Professor J. L. 

 Riddell, whose principles and 

 methods he has so fruitfully fol- 

 lowed. 



Meanwhile the original device of 

 Riddell which, as we have seen, he 

 himself had pointed out at the 

 Cleveland meeting, gave ortho- 

 scopic vision when used without 

 eye-pieces, was brought much earlier 

 into general use. The optical parts 

 of the binocular dissecting micros- 

 cope then exhibited by him have 

 been strictly copied in the binocular 

 dissecting microscopes made since 

 by Nachet of Paris, and at a later 

 period by R. and J. Beck of Lon- 

 don, both of which are still de- 

 servedly popular. 



Dr. Carpenter, in the work I 

 have cited, gives an excellent de- 

 scription of the optical arrange- 

 ment of this instrument, which, 

 however, he erroneously credits to 

 Nachet {op. cit, p. 84), and remarks : 

 "To all who are engaged in investi- 

 gations requiring very minute and 

 delicate dissection, the author can 

 most strongly recommend MM. l^a- 

 chet's instrument " {op. cit., p. 85). 

 I agree perfectly with this opinion, 

 but " Nachet's instrument " is sim- 

 ply a copy of Riddell's. To Mr. 

 R. Beck Dr. Carpenter ascribes {op. 

 cit., p. 83), a different arrangement, 

 in which two of Riddell's four 

 prisms only are used to bring one- 

 half the cone of rays from the ob- 

 jective to one eye, while the other 

 half of the cone reaches the other 

 eye without the interposition of any 

 prism. To this arrangement. Dr. 

 Carpenter says, Nachet's (that is 

 Riddell's) is greatly superior. The 

 Becks appear to have arrived at the 

 same opinion, for a binocular dis- 

 secting microscope purchased of 

 them for the Museum about ten 

 years ago, is made strictly after 

 Riddell's pattern. 



Nachet certainly at least deserves 

 the ci'edit of having highly appre- 

 ciated this tirst plan of Riddell, for 

 he not merely employed it for his 

 dissecting microscope, but extended 

 its usefulness by applying it to the 

 ophthalmoscope, thus obtaining bin- 

 ocular vision with that instrument. 

 The binocular ophthalmoscope of 

 Murray and Heath is also made on 

 the same principle, differing only 

 in the mechanical contrivances em- 

 ployed. (See A. Zander, The 

 Opthalmoscope, translated by R. 

 B. Carter, London, 1864, p. 58 et 

 seq.) 



One word before concluding with 

 regard to the remark of Professor 

 wheatstone, who, as we have seen, 

 declared after reading the reprint 



