ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



807 



Fig. 216. 



diameter, and has a focal distance of 14 cm. It magnifies about 5 times. 

 The advantages claimed for this instrument are that with No. 1 lens both 

 eyes can be used at once, the field of vision is considerable, and both hands 

 are left free for manipulation. If greater magnification be desired, No. 2 

 lens is easily put in position, or both may be employed at the same 

 time. 



Vogel's Lens-stand for Entomological purposes. * — This apparatus 

 (fig. 216), has been for many years used by Prof. H. C. Vogel in the study 

 of small insects. 



On a horseshoe foot A is a brass pillar B, which carries a conical 

 piece C to hold the lenses. T is the stage which is raised or lowered on 

 the pillar B by rack and 

 pinion, and so focused to 

 the lens L. The lenses 

 supplied with the apparatus 

 are all set in conical fittings 

 which drop into C. The 

 important feature of the 

 apparatus is the facility 

 for moving the stage into 

 any desired position. It 

 consists of a cork T, set in 

 a brass ring, terminating 

 below in a milled head r, by 

 which the stage is rotated 

 in its own plane, while by 

 the milled head K it can be 

 rotated about a horizontal 

 axis a a. This axis is also 

 made to slide in its bearings, 

 so that different small ob- 

 jects fixed in a line on T 

 can be successively brought 

 into the centre of the field. 

 Thus, the object m when 



placed at a point on the prolongation of a a, is capable of a fourfold move- 

 ment without having materially to alter the focal adjustment. D is the 

 illuminating lens which slides along a brass pillar fixed in either of two 

 holes upon the ends of the horseshoe foot, so that the object can be illumi- 

 nated from either side. This lens may also be conveniently used in 

 mounting large objects, for which purpose it is raised to the top of the 

 pillar and swung round to occupy the position of which is thrown back. 

 For transparent objects the cork is replaced by a glass plate. 



Westien's improved Universal Clamp for Lens-holders, &c. f — The 

 clamp of Herr H. Westien, the construction of which was described in 1885,| 

 has since received improvements which have not only made its production 

 easier but have considerably widened its field of utility. This clamp renders 

 it possible by a single screw motion to clamp securely to an upright an 

 object provided with a bar of any form, whether round, oval, trianf^ular, 

 square, or flat. The upright may also vary in size from 2-9 mm., from 



* Zeitschr. f. Instrumentenk., vii. (1887) pp. 173-5 (1 fig.). 



+ Ibid., pp. 54-5 (1 fig.). 



; See this Journal, 1885, p. 316. 



