ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
The apparatus works in the following way : — The water in the 
reservoir a is heated by a mineral oil lamp. The current of hot water 
rises through the middle pipe to the upper compartment of the reservoir 
and passes down into the thermostat through the pipe on the left, and 
returns by the pipe c. 
On reference to the illustration it will be seen that when the ball d 
sinks the ball e rises and the hot current will be diverted into the pipe 
c, and the stream pass in the 
contrary direction back again Fig. 44. 
into the reservoir a In this 
way the equilibrium of the 
water-heat in the thermostat 
is maintained. 
The automatic rise and fall 
of the balls is brought about 
by the attraction and repul- 
sion of the armature g by an 
electro-magnet while the open- 
ing and closing of the electric 
current ( h is a Meidinger’s 
element) to the magnet is 
effected by the rise and fall 
of the mercury in the regu- 
lator i. The latter is an ordi- 
nary Reichert’s regulator with- 
out the upper funnel. One 
end of the conducting wire is 
connected with the upper end 
of the regulator, the other with 
the side branch. When the 
water gets too hot the mercury 
rises and touches the upper 
wire and so closes the circuit. 
The armature g is attracted and the ball e drawn up, while d sinks down 
and thus the hot water ceases to pass into the thermostat. When the 
water cools the mercury sinks and the current is broken, the balls assume 
their former position and hot water again passes into the thermostat. 
The author is extremely satisfied with the working of the apparatus. 
Heydenreich’s Regulator and Remarks on Thermostats.* — Dr. L. 
Heydenreich describes a modification of Altmann’s thermo-regulator f 
which he has used for some time and has found to be very sensitive. 
The reservoir A F contains mercury above which is a layer of ether. 
When the temperature of the water mantle becomes too great the ether 
vapour presses on the mercury and the latter rises in the tube FAB 
until it reaches the bifurcation, when it prevents the gas from passing 
along in the direction D B C, permitting only a small stream to flow 
through E, a stream just sufficient to keep the burners alight. To en- 
sure more perfect accuracy of regulation the wall of the reservoir should 
* Zeitschr. f. wiss. Mikr., ix. (1893) pp. 300-G (2 figs.), 
f This Journal, 1891, p. 651. 
2 D 
1893 . 
