128 SUMMARY OF CURRENT RESEARCHES RELATING TO 



In 1867, Dr. Woodward, ofWashington, forwarded to Dr. Maddox 

 for exhibition to the Society, a series of micro-photographs of Podura 

 scales, and various other test objects produced with sundry objectives, 

 notably Powell and Lealand's J^j, 0^5, and J^ dry lenses. The ampli- 

 fications did not exceed 2100 linear. Dr. Maddox then remarked that 

 he believed " the Podura scale had never yet, in this country, been 

 photographed by a J^-" The Navicula rhomhoides, by Wales's | and 

 amplifier, magnified 800 linear, was especially admired.* Shortly 

 afterwards. Dr. Woodward presented to the Society a large series of 

 micro-photographs of Nobert's 19-group test-plate, and other test 

 objects — the direct amplifications not exceeding 2000 linear. 



At various dates micro-photographs have also been brought before 

 the notice of the Society by Dr. Maddox, Dr. Woodward, Count 

 Castracane, Mr. S. Wells (of Boston), and others, and the direct 

 amplifications have rarely exceeded 2000 linear. 



In 1868, Mr. Charles Stodder, of Boston, having access to a 

 number of the presumably best objectives in America, was content to 

 specify his own magnifications as not exceeding 1062 linear (though 

 he referred to 6000 obtained by Messrs. Sullivant and Wormly),t and 

 he particxxlarly commended the performance of Tolles's ^ immersion, 

 as " the best on record " — and yet the magnification was only 550 

 linear for the resohition of Nobert's 19th group.| 



It is to be supposed that experienced microscopists like these have 

 in every case sought to do full justice to the objectives in their hands, 

 and it may be noted particularly that with so difficult an object as the 

 highest group on Nobert's 19-group plate. Dr. Woodward, down to 

 the latest date on record, has limited his micro-photographic operations 

 to less than 2000 linear of direct amplification. His more recent series 

 of micro-photographs comprised A. pellucida, both dry and in balsam, 

 the magnifications hardly exceeding 3000 linear, though the objectives 

 included ^^^, -jJ^, and ^ immersions of Powell and Lealand, ^^ and -^ 

 immersions, and -^^ oil-immersion of Tolles, y'^ glycerine immersion of 

 Spencer, i and ^ oil-immersion of Zeiss. The last objective named he 

 regarded as the most powerful " resolving " lens he had seen up to the 

 date of his communication (October 1879). Dr. Woodward has then 

 been contented with about 3000 linear to exhibit the best definition of 

 the objectives in the well-known official collection of the Army 

 Medical Museum at Washington. 



At p. 821, two micro-photographs of P. angulatum, by Giinther, of 

 Berlin, were referred to ; they were produced with Gundlach's No. VII. 

 immersion, the direct magnifications respectively 2000 and 5900 

 linear — obtained by receiving the images at conjugate distances of 

 1 metre and 3 metres (nearly). These excellent j^rints have since 

 been received, together with one of Frustulia saxonica in balsam, mag- 

 nified about 5000 linear (enlarged from the original photograph), 

 showing an appearance of beaded structure even more palpably than 



* Quart. Journ. Micr. Sci., No. xxix. (1868). (Pjoc. K. Micr. Soc, p. 63.) 

 t Amer. Journ. Sci., Jan. 1861. 



i See reprint of Mr. Stodder's paper on " Nobert's Test-plate,"' &c., Quart. 

 Journ. Micr. Sci., No. xxxi. (1868) pp. 131-8. 



