1185 
and two platinum resistance thermometers Pt, and Pt, as used 
for the determination of the diameter of hydrogen *)) passes through 
it and-by the holes in the lid # enters the space /#, above; it is 
then carried through the vacuum tube 6,, into the space surrounding 
the spiral 4,, by which the gas inside acquires a preliminary cooling, 
and finally escapes by bj, to a gasometer. 
The half automatic regulation of the temperature is very simple 
in principle. By the resistance W, the gas is heated to the desired 
temperature, the current being furnished by the accumulators A; (36 
volts) and adjusted by the regulating resistance W 3. The gas-ther- 
mometer //, already referred to, which is connected with the 
manometer through the capillary. C, provides for the automatic 
closing and opening of the current, in a manner easily understood 
from the figure. As long as the temperature is too low, the mano- 
meter being properly adjusted, there is electric contact at D; when 
the temperature rises above the desired value, the contact is broken. 
When the cryostat is in action and everything properly regulated, 
the automatic arrangement is continually in action and the current 
is opened and closed at regular intervals (of say 10 or 20 seconds). 
When this arrangement was tested, it appeared from the readings 
of the platinum resistance thermometers that owing to some inertia 
in the automatic action small fluctuations of the temperature in the 
experimental space of ‘02° to ‘03° were still present. With a view 
to a still finer regulation the resistance W, was then introduced 
in the space £5. 
The current through this small resistance is furnished by an accu- 
mulator A, aud is regulated by hand by the observer at the galvano- 
meter by means of the regulating resistance W,. The deflection of 
the galvanometer shows the small variations of temperature much 
more quickly than the automatic regulator can act and the observer 
is able by a change of W, at once to bring back the temperature 
to the desired value. In this manner it is possible to keep the tem- 
perature constant to .01°, sometimes during hours. 
The connecting wires of the various resistances are only shown 
diagrammatically in the figure. Thus ZL, represents the 4 wires of 
the automatic regulator and the resistance W,, L, the eight wires 
of two platinum resistance thermometers Pt, and Pt, 
One of the principal desiderata in the previous simpler cryostat 
was the possibility to make visual observations in the space #. The 
apertures which had originally been made in the copper mantle for 
1) E. Maruias, C. A. CROMMELIN and H. KAMERLINGH ONNES, these Pro- 
ceedings 23, p. 1175, Leiden. Comm. N°. 1545. 
