ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



413 



there being a blackened brass cup to fit into it when desired. A hemi- 

 spherical glass lens fits in the same hollow, " optical contact " being 

 made between the paraboloid and the lens by glycerine and a homo- 

 geneous medium. There is also an opening in the side for the 

 admission of light, all other light being stopped out. 



The apparatus can thus be used as a Wenham reflex illuminator 

 or an ordinary paraboloid, at the same time providing a hemispherical 

 lens if required. 



Browning's Simple Heliostat. — Fig. 79 shows a simple form of 

 heliostat for the Microscope, It is provided with three movements : 

 — (1) The rotation in the vertical j)lane of the inner cylindrical 

 fitting, carrying the mirror arm, on the fixed toothed disk, by the 

 large milled head ; (2) The in- 

 clination of the mirror in the Fig 

 double gimbal fitting by means of 

 the endless screw (milled head to 

 the right) acting upon a counter- 

 sunk worm on the posterior sector 

 forming the inner arc of the 

 gimbal ; (3) The rotation of the 

 entire gimbal-mounting of the 

 mirror by the milled head beneath 

 (this movement serving princi- 

 pally for the first adjustment of 

 the mirror to the direction in 

 the horizontal plane in which the 

 reflected beam is to be utilized). 



The particular heliostat figured 

 was adapted for mounting in the 

 substage of a Microscope which in 

 that case would have to be inclined 

 so that the optic axis is parallel 

 with the pole of the earth. The 

 mirror being then adjusted to the direction rec[uired, the beam of 

 reflected light would be maintained on the same spot by the simple 

 rotation of the mirror arm on the toothed disk, acting as the hour 

 circle of an equatorially mounted telescope, the inner gimbal arc 

 acting as the declination circle. 



It can also (and probably better), be mounted vertically upon a 

 separate stand apart from the Microscope, or in a shutter exposed to 

 a southern aspect. 



Hayem and Nachet's Modified Haematometer. — This is now 

 arranged as shown in Figs. 80-82, and is thus described by M. 

 Nachet : — 



" The hsematometer, formed of a cell with a flat base, devised by 

 Dr. G. Hayem and myself some years ago, has been adopted by the 

 different authors who have experimented on the number of the blood- 

 corpuscles. Some modifications have been made in the apparatus, 

 without changing it essentially, amongst which may be noted the 



