( 134 ) 
a, @ and caoutchoue packing. The line joining the upper couple 
has been turned about the axis of the case with respect to the line 
joining the lower couple, in order to obtain a sufficient illumination 
of the issuing jet '). 
The loose bottom Wi, which may be pushed outward by inner 
pressure, rests on exhaustion with the border W, on the border of 
the case, and is sufficiently strengthened by ribs to be able then to 
resist the outer pressure. By means of the caoutchouc cap W,, 
which is stretched over the bottom and fastened air-tight to the 
borders once for all with the utmost care, a fitting is obtained, 
whilst nevertheless in case of accident the whole bottom would act 
as a safety-valve. 
The whole apparatus can be exhausted through the cock X,. This 
is connected together with the vaenum-manometer Xs to the case at 
ihe flange X; (dotted in the section, and depicted beside the case 
separately in section), to which the glass tube X; has been fastened 
in the same manner (by means of X,) as the observing tubes. In 
this tube P, O; is introduced for drying the apparatus. 
The whole inner wall of the case is coated with a layer of felt and 
the bottom with several layers while the inner surface of this layer 
has been rendered reflecting by lining it with nickel-paper. The thin 
Jayer of nickel however has been removed over a length of a few 
centimeters at all places where heat might be supplied to it by 
conduction. Where the inside of the case or of the observing and 
illuminating-tubes - has not been coated with felt, or a layer of felt 
would not be rigid enough, insulation has been secured by intro- 
ducing wood or caoutchouc, as appears sufficiently from the drawing °). 
The dust-box Y, provided with an extremely light valve Ys 
opening outward, and made of cotton wool enclosed between gauze 
with a border of wash-leather, allows the gas to escape without 
appreciable fall of pressure and prevents the gas, which might flow 
1) Further explanation of symbols: zr, x. loose-fitting, thin plate-glasses, separating 
the back observingtube-chamber from the case, while nevertheless the pressure of 
the gas in the case and the observing tube remains equal; ¢,, ¢, wooden packing 
tubes, in order to supply as little heat as possible to the gas in the observing tube- 
chamber; ¢,, ps thick observing glasses, fitting air-tight in ws, and further fastened 
by means of bands v,, vs; 9), @ caoutchouc-tubes, fitting round the brass-ring of 
foremost observing tube-cliamber; @,, w, observing-glasses cemented in border, with 
packing fitting on mj, ro; &, & tubes serving for sucking dry, heated air through 
foremost chambers (commonly eicsed). In the various chambers stand drying-dishes 
with P,; O;. The tube at ¢, should have been drawn broken off. 
*) The case has room to’ place still another athermanous layer between the wall 
and beaker B, 
