1187 
§ 2. Description of the cryostat *). 
The eryostat consists of two vacuum vessels, viz. an evaporator 
V and cryostat B, both enclosed in vacuum vessels with liquid 
air V, and B, and closed by german silver lids or caps Vy and By. 
The principle of the apparatus consists in the experimental space 
E being kept at constant temperature by a current of gaseous 
hydrogen, the temperature of which is kept at a definite value by 
automatic regulation of an electric current through a heating wire. 
Let us follow the gaseous hydrogen on its way through the 
apparatus, as shown by the arrows. At 6, it enters under small 
excess of pressure. For the manner in which the current is kept 
constant and regulated. we refer to fig. 6 of the previous paper on 
the vapour cryostat. It then flows through the copper spiral 6,, 
which is cooled, as will appear presently, by the waste hydrogen, 
and the tube 53 (of german silver in order to minimize the supply 
of heat to the liquid hydrogen below) from which it escapes at 
6, bubbling up through the liquid hydrogen which fills the evaporator. 
In this manner a fairly strong and regular evaporation of the 
liquid hydrogen is obtained; the hydrogen vapour passes into the 
tube Ds, which continues as a spiral under the liquid hydrogen, 
and hence into the double walled vacuum tube be which carries 
the gas (cooled to about — 253°) to the lower end of the cryostat at 67. 
Here it enters the spiral-shaped heating space £, (see also section 
V—VI) and flows round a heating wire W, which heats the gas 
to about the desired temperature by means of an automatically 
regulated current. The space 4, communicates at the centre through 
a hole with a second space KE, above it. Here the gas first passes 
along a copper thermometer bulb H, (which serves for the regula- 
tion of the temperature, as will be explained further down), then 
along a resistance JW, and finally rises through 6, into a thickwalled 
copper tube going four times up and down, the horizontal parts of 
which are seen in section III—IV at bo, the vertical soldered on 
the outside against the very thick copper mantle (for the purpose 
of a uniform temperature) of the experimental space 4; this motion 
up and down serves to communicate the required temperature to 
the copper mantle. Finally the gas enters the experimental space 
# with the measuring instruments (in the figure a dilatometer D 
1) We here refer to Leiden Comm. N°. 15la (these Proceedings 19, p. 1049) 
where many constructional details are mentioned and the principle of the 
apparatus is explained; at the same time the present description is so arranged, 
that it may be read and understood by itself. 
