1662 
disk S on which rests the cylinder ( (of aluminium or copper; see 
lower down). The whole system which forms the oscillating part: 
was worked on the lathe as exactly as possible to a body of revolution. 
The sphere B is surrounded by an almost completely closed copper 
spherical shell 5’ of internal radius 2.92 ems. and thickness 1 mm. ; 
this shell consists of two separate halves (an upper and a lower 
half), which fit exactly and are forced together by means of small 
springs. The lower half is at the bottom provided with a small 
hole for admitting the liquid; the upper half bas at the top a larger 
circular hole (radius about 1 em.) and carries a copper tube B,, 
which is provided with two pairs of opposite windows; the tube 
with the spherical vessel attached can be moved up and down on 
a copper ring A, whieh is soldered to a glass tube B, and can be 
fixed at a suitable height by means of a clamping band with screw. 
The system of concentric spheres is placed inside a partially sil- 
vered vacuum-glass G, which holds the liquid gas. The glass is 
mounted in a copper fitting which by means of copper rings with 
rods is attached to a metal cap resting on a thick copper plate by 
means of levelling screws; this plate is fixed to the same wooden 
board as the slide mentioned above. 
The cap is constructed on the same plan as in the other apparatus 
used for similar purposes in the cryogenic laboratory. It consists of 
two parts: a conical part made of german silver with a tube for 
pouring in the liquid gas and a tube for conveying away the vapour ; 
this part fits over the rim of tbe vacuum-glass and is connected to 
it air-tight by means of a rubber band, the second part being 
a cylinder of copper provided with two opposite side-tubes, which 
are closed by disks of thick plate-glass; this cylinder is fixed in a 
copper ring which carries the levelling screws on which the cap 
rests. The two parts of the cap are separated from each other by 
a partition with a circular opening, which is just wide enough to 
transmit the glass tube B, with the lower glass tube; moreover 
to the lower end of the cylinder a copper cone is soldered which 
ends in a tube, into which the glass tube B, is soldered’). 
At the top the copper cylinder is closed by a ring-shaped disk, 
on the top of which a long glass tube B, is sealed’); this disk has 
1) By this means the part of the apparatus above the partition is practically 
separated from the part below, where the low temperatures are; this space with 
the cylinder C contained in it therefore remained practically at the temperature 
of the room, as shown by the readings of a thermometer which was immersed 
in water poured into the small tray formed by the lid of the cap (cf. figure). 
*) The wire D is almost completely enclosed in this tube and thus remains 
practically at room-temperature. 
