1034 SUMMARY OF CURRENT RESEARCHES RELATING TO 



EoRERT, S. — An Appliance for making Photo-micrographs with the Microscope in 

 the upright position. 



[Simply a riglit-angled prism.] 



The Microscope, VIII. (1888) pp. 310-2 (2 figs.). 



Fhotomicrographic Apparatus, Some. 



Scicntijic Xeir:i, II. (1888) pp. 3G1-2 (1 fig.), 378-9 (2 figs.), 402-3 (2 figs.). 



Schmidt & Haensch, Die neue verbesserte Vergrossernngsoamera von. (The new 

 improved enlarging camera of Schmidt aud Haensch.) 



Phot. Mitthdl. V. Vogel, I. (1888) February, 4 pp. 



Zeiss, C. — Special-Katalog iiber Apparate fiir Mikrophotographie. 4to, Jena, 1888. 

 C5) Microscopical Optics and IXauipulation. 



Microscopical Optics and the ftuekett Club Journal. — Our remarks 

 on tliis subject at p. 817 bave produced letters from Mr. II. Morland 

 and Mr. T. F. Smitb,* tbe two authors whoso papers were referred to, 

 aud also from " A Member of both Societies.! These letters illustrate 

 in so marked a manner what wo desired to enforce, that we deal with 

 them further here. 



One of Mr. Morland's original blunders was expressed in the following 

 words : — " The only objection to my mind against this medium is that 

 " its refractive index is not sufficiently high for the new immersion 

 " lenses " ! It is almost incomprehensible that notwithstanding the time 

 that has elapsed he shoiold not have appreciated the absurdity of what 

 he thus propounded ; but in the letter now published not the faintest 

 glimmer is shown of any recognition on his part that his statement was 

 as absurd as an assertion that the power of a telescope depends upon 

 whether it is encased in wood or brass. 



But if Mr. Morland's want of appreciation of the principles of the 

 subject with which he was dealing is surprising, what are we to say to 

 Mr. Smith's letter, which contains the most astounding microscopical 

 mare's nest propounded since the days of the old aperture controversy. 



It is hardly credible, but it is the fact, that Mr. Smith now justifies 

 his original criticisms on the difli-action theory, and which we ventured to 

 describe as " terrible nonsense," by the statement that that theory rested 

 on objectives of low apertiu'es, and that subsequently " the aperture of 

 objectives has been increased by nearly one-half," so that adherence to 

 the theory in the present day is " nothing better than superstition." 



The first remark on this statement is that when the difii'action theory 

 was propounded, we had not merely di-y objectives with a theoretical 

 maximmn aperture of 1 • N.A,, but water-immersion objectives with 

 1'33 N.A., so that in the advance to 1*52 N.A. there is an increase not 

 of nearly one-half or 50 per cent., but of 15 per cent. only. The second 

 remark is that Mr. Smith is by his own admission wholly unaware that 

 the theory was restated by Prof, Abbe after homogeneous-immersion 

 objectives had come into use, and that in 1882 it was again developed 

 by him in the fullest detail. J 



The letter of " A Member of both Societies " points the moral to 



* Eng. Mech., xlviii. (1888) p. 178. t Ibid., p. 159. 



X ]\Ir. Smitli's idea as to Pruf. Abbe in 1875 "never having dreamt of the possi- 

 bilities of tbe present objectives " is still more comical when it is considered what 

 has been published in this Journal by Prof. Abbe ou that very point, and the same 

 remark applies to his views on " doubliug the illuminating power," and " observing 

 by direct light." 



