ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
525 
useful for bacteriological and other purposes. The water-vessel, to hold 
10-40 litres, is made of enamelled iron. Near the bottom is a floor 
made of brass bars M ; beneath this is the U-tube, filled with 30 per cent, 
chloride of calcium solution, and the regulator r, which stops off access 
of gas to the flame in the usual manner by means of mercury. 
An equable temperature of the water is effected by the working of 
the four scoops n driven by the fans /, which are set in motion by a 
gas flame e. The connecting-rod between the fans and the scoops is 
pivoted in an agate cup a. The water is maintained at a constant level 
by means of a siphon apparatus. 
Flasks are fixed in position within the thermostat by means of the 
clamps shown in fig. B, or placed on the floor M, as at c. Test-tubes 
may be suspended by the device shown at d. Here they are placed in a 
cork which is jammed in between the two parallel bars. 
Over the air thermostat this water thermostat possesses these advan- 
tages : — the cultivations are more rapidly brought up to the temperature 
of the surrounding medium, the water temperature is but little altered 
on the insertion or removal of the flask, and a greater constancy of 
temperature is attained. 
(4) Photomicrography. 
Baker’s Photomicrographic Apparatus. — This apparatus, as recently 
supplied to Mr. Andrew Pringle, is shown in fig. 65. It consists of a 
substantial teak base-board 6 ft. 11 in. long, and 1J in. thick, on which 
the camera with its support is placed, the other end carrying a teak-wood 
turntable clamping to the base. On the turntable a quadrangular metal 
frame is fixed, having a metal trestle to support the upper end of the 
limb of the Microscope when in the horizontal position, and two clamp- 
screws are fitted to receive the front feet of the Microscope. By this 
arrangement the instrument readily serves both purposes, either for 
ordinary observations or for photographing, the attachment in the latter 
case being easily and rapidly effected. The compound bull’s-eye con- 
denser, with centering adjustments, is carried by a pillar attached to the 
turntable ; and beyond this is a support for the oxy-hydrogen lamp 
which is furnished with the usual mechanism for regulating the position 
of the lime-cylinder. 
The Microscope is that known as the Nelson model, having the 
differential-screw fine-adjustment with actuating milled head at the 
lower end of the limb. It has a graduated rotating mechanical stage, 
and rackwork centering substage with differential-screw fine-adjustment. 
The body-tube is 150 mm. long, with racked draw-tube and an extra 
sliding draw-tube extending to 300 mm. An adapter with Society screw 
is fitted to the sliding draw-tube to allow the use of low-power objectives 
without racking the body-tube too far from its normal bearings, by which 
method the field of the objective is not cut off by the body-tube. The 
nose-piece is removable. The camera can be used at any length from 
6-50 in. ; it is provided with an exposure shutter and with a con- 
necting tube sliding easily into a cap fitting on the eye-piece end of the 
Microscope. The camera can also be moved laterally and clamped to the 
base-board. 
Focusing-rods run the whole length of the base-board, and con- 
