1660 
taken on the suggestion of Professor KAMERLINGH Onngs. Since the 
apparatus which we have designed for the purpose *) has been found 
to work satisfactorily, we can now proceed to its description. We 
shall add the preliminary results obtained with liquid air and three 
other mixtures obtained from air, one of which was almost pure 
oxygen, the other consisting chiefly of nitrogen. 
2. Description of the apparatus. 
The two principal parts of which the apparatus consists are the 
oscillating system and the vessel in which it is suspended and 
which contains the liquefied gas. 
The main part of the oscillating system is a carefully turned brass 
sphere B (comp. figure). Careful measurements proved it to be a 
faintly flattened ellipsoid of revolution, the equatorial radius FR, being 
1.927 ems. and the axial radius R, 1.923 ems.; its mass m,; was 
250.8 grms. The sphere is suspended from a wire D of phosphor- 
bronze, thickness 0.17 mm. and length about 60 cms. The wire is 
soldered to a small piece of copper which is screwed into the knob 4; 
K can turn in a conical hole in the thick plate P, which is attached 
at right angles to a slide S/; the latter is fixed toa vertical wooden 
board, which in its turn is fastened with iron bands to a stone column 
standing on a stone slab, which lies on a pillar built into the ground 
and is thus entirely independent of the building. By means of a 
micrometer-screw J/s the slide, and thus also the sphere, can be 
moved up and down, so that the centre of the sphere can be exactly 
brought to a desired level; moreover as the plate P is adjustable 
in two directions at right angles, the centre of the sphere can also 
be moved horizontally to any desired point. 
The wire is not immediately attached to the sphere, but to a 
small glass tube B, about 25 ems. long, which at both ends is sol- 
dered into a small copper tube. The lower one carries a steel pin 
St (length 7 ems, thickness 1 mm.) to which the sphere is screwed ; 
into the upper tube a piece of copper is screwed, into which the 
lower end of the wire D is soldered’). This tube also carries a small 
1) The apparatus was entirely constructed in the workshops of the cryogenic 
laboratory. 
?) The chief reason why the sphere is not directly suspended from the wire is 
that the latter must remain at the same temperature as much as possible, in order 
that its elastic properties may not undergo any change; it must therefore not 
reach down into the cold liquid. The only parts of the suspended system which 
are immersed in the liquid are the sphere and a part of the steel pin Sf, which 
is naturally taken as thin as possible, in order that its friction may be neglected, 
as it would be difficult to take it into account, 
