ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 119 



of the Curator, Prof. Meucci, we were enabled to secure a photograph of 

 it. Nothing was known as to the origin of the instrument, but from its 

 resemblance to the Microscope figured in plate i. of a folio work 

 entitled ' Description d'un Microscope et de differents micrometres, &c.,' 

 published in Paris, in 1768, by the Due de Chaulnes, we are able to 

 assign the design to him. 



The principal aim in the construction seems to have been to facilitate 

 the verification of micrometric measurements^, especially of micrometer- 

 divisions, for the production of which the Due de Chaulnes devised an 

 elaborate dividing engine in which he claimed to have embodied some 

 original methods of obtaining accuracy in dividing scales. 



The design of the Microscope proj)er, and of the eye-piece micrometer, 

 seems to have been copied to a considerable extent from instruments 

 made in England by John Cuif. The novelties were (1) in the applica- 

 tion of a stage of an unusually substantial character, supported by four 

 shaped legs on a framed base, the stage being arranged specially to carry 

 screw-micrometers acting on the object in rectangular directions ; 

 (2) the body-tube is supported both at tlie nose-piece and near the eye- 

 piece in centering sockets, by which the optic axis can be exactly 

 collimated. In the original figure the body-tube is not mounted with 

 these centering arrangements, and levelling screws are shown at each 

 corner of the base, while a rack-work is applied for the coarse-adjustment. 

 The Florence instrument is constructed more solidly than the one shown 

 in the Due de Chaulnes's figure, the extreme importance of solidity 

 being probably discovered more and more during the progress of the 

 construction. 



DipPEL, L. — Aus dem optischen Institute von Carl Eeichert in Wien. (From the 

 Optical Institute of Carl Eeichert in Vienna.) 

 [I. The new large stand, No. 1a. II. Tlie apochromatics and compensation 

 eye-pieces.] Zdtsch'-. f. Wiss. Mikr., v. (1888) pp. 145-50 (1 fig.). 



(2) Eye-pieces and Objectives- 



Monobromide of Naphthaline as an Immersion Medium. — Mr. H. 

 Jackson, of the Cliemical Laboratory, King's College, recommends this 

 substance, not only as a solvent for balsam in mounting, but more par- 

 ticularly as a medium for immersion objectives. The refractive index 

 is too high to use it alone, but diluted with castor-oil it gives excellent 

 results. The relation of its dispersive power to the refractive index 

 shows it to be both theoretically and practically superior to cedar-oil. 

 The smell of it after remaining on the fingers for a little time is 

 unpleasant. 



C ZAP SKI, 8. — Compensationsocular 6 mit 1/1 Mikron-Theilung zum Gebrauch 

 mit den apochromatischen Objektiven von Carl Zeiss in Jena. (Compensation- 

 ocular 6 with 1/1 micron graduation for ute with Zeiss's apochromalic ob- 

 jectives.) 



[Cf. this Journal, 1888, p. 797.] Zeitschr. f. Wiss. Mikr., v. (1888) pp. 150-5. 



(3) Illuminating' and other Apparatus. 



Thoma's Camera Lucida.*— Prof. Dr. E. Thoma considers that the 

 ordinary form of camera lucida is unsatisfactory for low magnifications 

 (1-6). Moreover no account is taken of the refractive condition of the 



* Zeitschr. f. Wiss. Mikr., v. (18S8) pp. 297-301 (4 figs.). 



