1056 
nection parallel to the main circuit (see fig. 6) by which means a 
rise of temperature is started and an automatic regulation of the 
temperature is brought about. 
§ 3. Remarks concerning auxiliary apparatus, details of working 
and the action of the cryostat. 
Both the evaporator and the eryostat-vessel are immersed in 
vacuum-glasses with liquid air; the one surrounding the cryostat 
B, (fig. 6) is completely silvered in order to reduce the radiation 
to the experimental chamber as much as possible; in silvering the 
vacuum-glass in which the evaporator is placed, V,, a strip along 
a generating line of the cylinder is left transparent, through which 
the evaporation of the hydrogen may be followed. 
In starting the cryostat it is first — with a view to saving liquid 
hydrogen — cooled down by blowing hydrogen of ordinary temperature 
from a supply-cylinder *) through a cooling coil immersed in liquid 
air into the evaporator. 
When the tin wire thermometer in the regulating and adjusting 
chamber indicates, that the temperature has gone down to about 
—100° C., liquid. hydrogen is brought into the evaporator and the 
supply of hydrogen of ordinary temperature is then started. 
The velocity of the hydrogen flowing through the experimental 
space is regulated according to the indication of a ’’spedometer” 
which is joined in on the way to the gasometers; it consists of a 
small horizontal plate 7, floating on the vertical gas-stream in a very 
slightly conical tube ,, (length 15 ems, diameter at the top 1.62 ems., 
at the bottom 1.50 ems) the height to which the plate is raised being 
read by means of the small horizontal ring a, which serves as an 
index on a scale which is placed along the lower part of the meas- 
uring tube ar 
The current of hydrogen of ordinary temperature which is supplied 
from high-pressure supply-cylinders H,H, through a reducing valve 
is further reduced in the manner shown in fig. 6 by the stopcocks 
ix, and K, in such a manner, that a regular stream of gas-bubbles 
(escaping to the gasometer) bubbles through a mercury column rv of 
an adjustable height. As an instance (applying to the measurements of 
which the subsequent Communications N°. 1514 and N°. 151c treat) about 
with a thin layer of mercury. When the contact failed to act, the shunt connection 
could also be closed by hand in accordance with the indication of the position of 
the float. 
1) It will thus be seen, that use is made of pure hydrogen throughout (distilled 
or purified, see Comm. N°, 94f 1. e. and 1095. Proc. XI, 2, p. 883. 
