226 



THE AMEKICAN MONTHLY 



[December, 



^ 



the whole he succeeded best when 

 he "altogether dispensed with re- 

 flecting surfaces," and obtained bin- 

 ocular vision by placing an achro- 

 matic prism behind the objective, 

 so as to act by refraction only. It 

 is true, as he relates, that without 

 employing erecting prisms, the use 

 of which by Riddell he criticises, 

 his arrangement would be " to some 

 eyes pseudoscopic," but he suggests 

 that " Probably habit would enable 

 us to judge of their true form 

 without being under the necessity 

 of resorting to a special expedient 

 for the removal of the deception." 



In the Spring of 1854, Mr. Wen- 

 ham having now read Riddell's 

 description of his second plan, as 

 reprinted in the Quarterly Jour- 

 nal of MicrosGopioal Science for 

 January, 1854, published an addi-. 

 tional memorandum (Jour, cited, 

 YoL II, 1854, p. 132), in which 

 he deprecated "the rather glow- 

 ing account which the American 

 Professor gives of the perform- 

 ance of his microscope," asserted 

 (on the basis of his own failures, of 

 course, for he had not yet seen Rid- 

 dell's instrument), that — " The bin- 

 ocular microscopes up to the present 

 time have done but little else than 

 afford a glimpse of the splendid 

 and substantial appearance that 

 nearly all microscopic objects may 

 be expected to bear when the in- 

 strument is brought near to a state 

 of perfection," and naively declared, 

 "I have abandoned all attempts at 

 making a binocular microscope with 

 two objectives, as I found that I 

 could not get even a pair of l|'s to 

 bear upon the object together." 



Mr. Wenham vainly continued 

 his efforts to perfect a refracting 

 binocular for several years subse- 

 quently, and as late as June 13th, 

 1860, read to the Microscopical So- 

 ciety of London a paper " On an 

 improved binocular microscope " 



(Trans., Vol. YIII, 1860, p. 154), 

 in which he reports his success in 

 obviating the pseudoscopic effect of 

 his earlier instrument, by modifying 

 the compound refracting prism in 

 such a way that the rays passing 

 through its right side were sent to 

 the left eye, and vice versa: and 

 claimed "that the thinness of the 

 achromatic refracting prism gives it 

 a great advantage in the quality 

 of definition over the double sys- 

 tem of reflecting prisms that has 

 been proposed." 



How well this improved instru- 

 ment performed I do not know, but 

 it could not have been very success- 

 ful, for less than six months later 

 Mr. Wenham abandoned it for a 

 simple and successful modification 

 of the reflecting prism of Ividdell. 

 December 12th, 1860, he read to 

 the Microscopical Society of Lon- 

 don {Trans., Yol. IX, 1861, p. 15), 

 his paper " On a new combined 

 Binocular and single microscope," 

 in which he described and figured 

 the binocular arrangement that has 

 since been so generally connected 

 with his name. In this arrange- 

 ment a single reflecting prism only 

 was used, which received the rays 

 proceeding from one-half of the ob- 

 jective: the rays from the other 

 half proceeded without passing 

 through any prism to one eye, while 

 those which were intercepted by 

 the prism underwent in it two in- 

 ternal reflections, and emerged at 

 such an angle as to reach the oppo- 

 site eye. He obtained in this way 

 a degree of success that, to use his 

 own language, "considering the 

 nature of the principle, could not 

 have been anticipated." 



Meanwhile the discovery of Rid- 

 dell had attracted no less attention 

 on the Continent of Europe. P. 

 Ilarting, the distinguished Utrecht 

 professor, relates {Das Mihroshop, 

 Braunschweig, 1866, Bd. Ill, S. 



