532 SUMMARY OF CURRENT RESEARCHES RELATING TO 



LoMMEL, E. — TTeber einige optische Yethoden und Instrrunente. (On some 

 optical mothods and instrumtutti.) 



[Contains methods for determining (1) the focal length of a lens, and 

 (2) refractive indices. Also spectroscope with internal slit. 



Zcitschr.f. InstnimcntcnL, V. (1885) i>p. 124-G (3 figs.). 

 Loudon, J.— Geometrical methods chiefly in the theory of thick Lenses. 



I'ruc. Canudinn Institute, III. (1885) pp. 7-17 (1 pi.). 

 MacMunn, C. a.— [Arrangement of the Microspectroscope.] 



ISi'pra, pp. 429 and 527.] Proc. Phi/siol. Soc, 1884, No. 4. 



Sec X„t'>rc, XXXI. (1885) pp. 326-7 (1 fig.). 

 Mayall, J., Jun. — Nobert's Enling Machine. 



Journ. Soc. Arts, XXXIII. (1885) pp. 707-15. 



See also Erujl. Mcch., XIJ. (1885) pp. 101 and 109. 



Journ. of Sci., VII. (1885) pp. 243-4. 



Knowledge, VII. (1885) p. 433. 



Journ. de 3Iicrogr.,'lX. (1885) pp. 176-8. 



Monocular v. Binocular. 



[Keplies in favour of the former by B.Sc, Enal, and E. A. Tindall. Also 

 remarks by R. D. R.] 



Engl. Mech., XLI. (1885) pp. 88-9 and 110. 



»» »» 



[Comments on B.Sc. 'a letter, ante, p. 835, by W. P. Oldham (pointing out 

 the unsoundness of B.Sc.'s advice, insisting that " the binocular is a 

 comfort, a pleasure, and a help," and protesting against the " undesirable 

 practice of sneering at one class of observers because they do not happen 

 to follow the particular line most favoured by another class"), by "A 

 Binocular M.D." (supix>rting the binocular and the use of the Microscope 

 '• as a means to an end, and that end is the pleasure derived from the 

 acquisition of knowledge"), and E. M. Nelson (each is best in its 

 own department. Tiie loss of definition with the binocular is (piite 

 inappreciable with tlie class of objects suitable for it), and F. D'Agen.'J 



Ibid., p. 132. 



[Remarks by F. D'Agen on R. D. R.'s letter, supra. "Many professional 

 readers would be delighted to hear of a cheap Stephenson's erecting 

 binocular with very short tubes (not 'having too great a slant), and fitted 

 with two powers, one like Zciss's variable low objective, and the other, 

 say, about 2/3 in. . . . If this ideal Microscope could further have wood 

 supports applied to stage (for hand rests), and be supplied at 5/. to 6/., 

 I may safely predict it would liave an enormous sale, and would do all 

 that any binocular can for natural history, dissection, &c. With such an 

 instrument, and one other for high powers, tlie scientific worker would be 

 completely armed. With regard to the high-power instrument, a very 

 short monocular one is best. . . . (The binocular is not of the slightest 

 advantage for high powers. The rest it aflbrds the eye can as suitably 

 be obtained by other plans without its expense and cumhrousness.) For 

 goniometric, polarization, and spectroscopic observations a totally distinct 

 instrument, or rather set of instruments, should be used. ... If makers 

 would give more of their attention to perfecting a set of instruments to 

 suit the varying requirements of different workers at as low prices as 

 possible, I think a decided improvement would set in. ... I do not 

 mean to contend that all attempts at combination are impossible, but 

 only that such combination in the main limit, and do not extend, tlio 

 advantages of the instruments so combined."] 



Ibid., p. 151. 

 M R E, A. Y. — Homogeneous Immersion Objectives. 



[Remarks in favour of correction collars, and as to the necessity for two 

 fluids (for central ami oblique light). Also as to a new Spencer 1/8 in 

 which it is claimed that " the difference in both chrf)matic and spherical 

 aberrations for the central and peripheral zones of the lenses has been 

 retluced to such a small residuum that there is practically no difference." 



