ZOOLOGSr AND BOTANY, MICROSCOPY, ETC. 819 



Furthermore, 



p-p =p-Y = p(^ --•) 



OP (a o\ 



p-p =p-^=n^-:^') 



By substituting these values in the equation /3' we get 



tt = 1 -f- (n' - 1)^,— ; 



-(-:-.) 





H = 1 + (w' - 1) ' ^ 



»"(>-„^-) 



9 



11/ ^\ O' - 9 



„ = 1 + (» - 1) ^:rg ' 



In conclusion, it only remains to be said that these forraulfe do not take 

 into account certain values which, if absolute precision were required, 

 ought to come into the calculation (distance of the objective from the 

 artificial lens, radius of curvature of the latter, &c.). Hence these formulte 

 give only an approximate result, but one which is sufficient for ordinary 

 and practical purposes. 



Dr. Martinotti might we think have found many better instances to 

 illustrate his text as to the want of novelty in sub-solar matters, as Prof. 

 Smith's apparatus is certainly a very useful device, and one for which he is 

 entitled to all the credit of independent invention. 



Davis, T. S. — New Stage Accessory. 



[Consisting of a slip of glass, from the surface of which a brass pin projects :it each 

 end. Over these pins another piece of glass, with corresponding holes drilled 

 in it, slides, and thus objects requiring to be flattened may be conveniently 

 secured for observation.] 



\6th Ann. Rep. S. Lond. Micr. and Nat. Hist. Club, 1887, p. 12. 

 Fasoldt's (0.) Eye-piece Micrometer. 



I " The Hues are said to be ground in the glass, not ruled."] 



Journ. New York Micr. Soc, III. (1887) p. 40. 

 Rogers' (W. A.) Stage Micrometer. 



I In squares upon speculum metal — parts of an inch and millimetn-.] 



Journ. Ntic York Micr. Soc, III. (\9.S7) p. 40. 



W IKK EL, R.— Apparat zum Markiren mikroskopischer Objekttheile. (Apparatus for 

 marking parts of microscopic objects.) 

 I Same as that described, ante, p. 468.] 



Ger>nan Patent, Kl. 42, No. 38858, 15th Sept., 1886 (1 fig.). 



C4) Pliotomicrogrraphy. 



Crookshank's Reversible Photo-micrograpMc Apparatus.*— Dr. E. M. 



Crookshank's apparatus (fig. 226) consists of a camera fixed upon a base- 

 board 4 or 5 feet in length, upon which the Microscope is clamped, and 



* Journ. and Trans. Photographic Soc. of Great Britain, xi. (1837) pp. 144-52 

 (1 fig.). See also Crookshank's ' Photography of Bacteria,' 1887, p. 22. 



