ox THE MEASUREMENT OF TExMPERATURE. 
179 
sealed to the capilla,ry tube B, which had an internal diameter of 0’5 milliin. 
When the lower portion of the tube B ■was cooled to the lowest temperature, it 
required a pressure of 60 atmospheres to compress the whole of the helium into the 
capillary tube. 
The pressure on the helium was determined by means of two gauges of the 
Amagat type, filled with nitrogen, and indicating 
pressures from 2 to 12 atmospheres, and from 8 to 60 
atmospheres respectively. 
The compression tube was filled with pure helium pre¬ 
pared in the manner described on p. 174 (fraction 1). 
In our first experiment the capillary compression tube 
Avas enclosed together Avith the thermometer Inilb, &c., 
in the apparatus shoAvn in tig. 1 (see adso p. 160). At 
temperatures betAA^een 20°'5 and 14° abs. (helium scale), 
the pressure on the gas was sloAvly increased to CO 
atmospheres, and then sloAvly reduced. Under all con¬ 
ditions the smallest change in the position of the mercury 
meniscus in the compressi^jn tube Avas ahvays accompanied 
by a corresponding change in the pressure. This experi¬ 
ment was repeated on three occasions. 
In another set of experiments, the capillary portion B 
of the compression tube passed through a rubber stopper 
E (fig. 6) into a small siB'ered A'acuum A'essel C, AA’ith a 
contracted mouth, enclosed Avithin a Avider glass tube D, 
sealed at the bottom to a tulie G, 7 millims. in diameter, 
and fitting closely to the rubber stopper E. The upper 
part of the tube D contained a plug of natural wool 
Avrapped in gauze, to shield the mouth of the vacuum 
vessel from radiation from above. A tube F jiassed 
through the stopper E, and Avas connected Avith a mercury 
manometer Avhich seiwed to measure the pressure in D. 
The vacuum vessel C Avas filled Avith liquid hydrogen "Fig. 6. 
and placed in the tube D, which was then rajiidly fitted 
to the rubber stopper E ; the compression tube B had previously been cooled Avith 
liquid air. A vacuum vessel H containing liquid air Avas then brought outside the 
tube D as in fig, 6. The tube G Avas connected Avith the double ‘ Fleuss ’ pump, 
arranged Avith the cylinders in scries (p. 161), and the pressure on the licpaid hydrogen 
AA'as reduced to 5 millims. of mercury, and maintained at that pressure for 20 minutes. 
Even at this temperature, which is probably not far below 13° abs., no evidence could 
be obtained that helium had liquefied. 
The extremely permanent character of helium confirms our vieAv that tliat gas is by 
