ZOOLOGY AND BOTANY, MICROSCOPY, EIC. 443 



MICROSCOPY. 



A. Instruments, Accessories, etc.* 

 CI) Stands. 



Fennel's Vernier-Microscope.t — Delicacy of ineasuremeut is, as is 

 well known, usually attained l)y the use of verniers, but it is frequently 

 necessary that the vernier should he a scale of considerable length. To 

 avoid the inconvenience arising from this length Fennel has revived an 

 old idea of Hensoldt's, and has introduced the vernier into the little 

 reading Microscope generally attached to graduated instruroents. The 

 whole vernier is easily contained in the centre of the Microscope field, 

 and there is no difficulty in reading off the graduations to 30'' or even in 

 estimating to a further 15". The designer calls this apparatus the 

 Microscope-nonius. Examples and full details are given by B. v. Hammer, 

 the author of the article. 



Nachet's New Stereoscopic Microscope with a Single Objective.| 

 In describing the stereoscopic binocular Microscope lately brought out by 

 Nachet (fig. 74), A. Quidor states that it is able to throw objects into 

 relief with a magnification of 10 to 400 diameters, whilst binocular 

 microscopes with two objectives cannot exceed 80 diameters. It has also 

 the double advantage over the latter class of instrument of not only 

 using objectives of very short (and consequently powerful) frontal 

 distance, but also of using ordinary microscopic objectives. 



The ray bundles produced by the objective are divided into two 

 symmetric parts by the rhombs P^ and Po, and the observer obtains the 

 relief by the fusion of the two conjugate images A^Bj and AoBg of the 

 object AB. As in all stereoscopic instruments, the distance of the oculars 

 must be equal to the pupil width of the observer's eyes. This adjust- 

 ment is obtained by the simple rotation of the prisms P^. Nachet's 

 stereoscopic Microscope, however, by the use of special oculars, also 

 suppresses all tendency to convergence and consequently fatigue. This 

 is a precious advantage both for myopia and for hypermetropia. The 

 instrument is essentially a development of the binocular Microscope of 

 Xachet pere, and is in accord with the principles of stereoscopy elsewhere 

 advanced by the author.§ The conjugate images of a micrometer object 

 subdivided into tenths are such that, when drawn successively by the 



* This subdivision contains (1) Stands ; (2) Eye-pieces and Objectives ; (3) 

 Illuminatiug and other Apparatus ; (4) Photomicrography ; (5) Microscopical 

 Optics and Manipulation ; (6) Miscellaneous. 



t Zeitschr. f. Instrumentenk., xxxii. (1912) pp. 148-54 (2 figs.). 



X Comptes Rendus, civ. (1912) pp. 68-70 (1 fig.). 



§ Ann. de Phys. et de Chimie, 1910. 



2 H 2 



