1034 SUMMARY OP CURRENT RESEARCHES RELATING TO 



He nest changed tlie water-imm. 1/12 for a water-imm. 1/16 of less angle, 

 which would barely resolve the A. peZZi(Ci(^a— that is to say, would only 

 resolve it in patches, and not from end to end. On examining this with 

 the prism, he found that the parts which were unresolved were still 

 unresolved ; but those parts which were resolved were intensified. 



"The image of A. jpellucida with an apochromatic 1/8 (1*4 N.A.), my 

 new eye-piece, and the prism is something very fine, such as I have never 

 seen before." 



He also tried the prism with several very subtle direct light tests, but 

 cannot say that he found any improvement in the image. On the whole, 

 he should think this class of objects would be seen better without the 

 prism. Probably the efficacy of the prism, when used with a lined test, 

 lies in the fact that it intensifies the diffraction spectra when it is placed 

 in a certain direction to it. 



Brokenshire, F. E. — Measnrement of Magnifjdng Power of Micro-objectives. 

 [Complaint that the subject has not received the elucidation he anticipated.] 



Ungl. Mech., XLVI. (1887) p. 300. 

 DiDELOT, L. — Du pouvoir amplifiant du Microscope, determination theorique et ex- 

 perimentale : suivi d'une table a qnatre decimales, des inverses de 1000 premiers 

 nomhres de • 01 a 10 • 00. (The magnifying power of the Microscope. Theoretical 

 and experimental determination : followed by a table to four places of decimals of 

 the reciprocals of 1000 prime numbers from 0"01 to 10 "00.) 



2nd ed., 90 pp., 2 pis., 8vo, Paris, 1887. 

 G ART EL. — Quelques generalites sur les instruments d'optique. (Some general con- 

 siderations on optical instruments.) 



Arch. Sci. Phys. et Nat., XVIIT. (1887) pp. 339-41. 

 HoDGKiNSON, A. — On the DifEraction of Microscopic Objects in Relation to the Re- 

 solving Power of Objectives. Proc. Manch. Lit. and Phil. Soc, XXV. (1886) p. 263. 



(6) Miscellaneous. 



" The Microscope as a factor in the establishment of a constant of 

 nature."— The following is the first part of the Presidential Address 

 delivered by Prof. W. A. Eogers before the American Society of Micro- 

 scopists at the Pittsburg Annual Meeting :* — 



" Microscopy is a cosmopolitan science. We may go farther than this, 

 and say that microscopy is more nearly cosmopolitan in its character than 

 any other science. If I did not believe this to be true I should not have 

 consented to occupy the honourable position which I now hold by your 

 suffrages, for there are many members of this Society to whom the honour 

 more justly belongs by virtue of greater familiarity with the technics of our 

 science. I suppose that I am indebted to this expression of your confidence 

 on account of the use which I have made of the Microscope as an essential 

 factor in a single line of research. 



It is the glory of our science that the Microscope supplements the 

 natural vision to such an extent that we can submit nearly every theory, 

 nearly every deduction from experiment, nearly every fact of observation, 

 to the supreme and only test by which a real truth in nature can be 

 established, viz. through the medium of one of the senses with which we 

 have been endowed by the Creator. It has been said that microscopy has 

 no claim to be regarded as a science, and that the Microscope is simply an 

 instrumental agent occupying with respect to other sciences a position 

 similar to that which the telescope sustains in its relation to astronomy. 

 A convinciag answer to this criticism is found in the fact that the telescope 

 is limited in its application to a comparatively narrow field of research. 

 Where the telescope answers a single question the Microscope answers a 



=^ Microscope, vii. (1887) pp. 2.57-61. Corrected by Prof. Rogers. 



