{ 815 ) 
pieces were used; first the cylindrical pole-pieces with quite flat end 
surfaces that had been used for the measurement of the magnetic 
rise, and then truncated conical pole-pieces the end surfaces of which 
(slightly concave, see in this connection p. 818) were 4 cm. in dia¬ 
meter, and the side surfaces of which were connected by convex 
surfaces of revolution to the cylinders that formed the cores; these 
were 9 cm. in diameter. These pole-pieces were constructed to give 
the strongest possible field when the distance between the poles was 
taken to be 20 m.m. By this means a field of about 16000 gauss 
was obtained. 
Our observations were made with an ellipsoid that was diamagnetic 
with respect to the surrounding medium — a solid silver ellipsoid 
immersed in a bath of liquid oxygen. The ellipsoid was turned by 
the “Societe genevoise pour la construction d’instruments de physique” 
from a block of very pure Merck silver. A preliminary experiment 
showed that it was very slightly diamagnetic with respect to air, and 
that this was quite negligible with respect to the liquid oxygen. The 
axes were measured microscopically on the dividing engine; this gave 
major axis = 1.0973 cm. and axis of revolution = 0.3654 cm. 
Furthermore, two intermediate ordinates parallel to the axis of 
revolution were measured on the dividing engine, and they were 
found to be 2% greater than the corresponding ordinates of a perfect 
ellipse with the same axes. This deviation from ellipsoidal shape was 
confirmed by a direct determination of the volume from the weight 
and the density, which gave 
0.2329 c.c, 
while calculation from the dimensions of the axes gave 
0.2308 c.c. 
In the calculations we made use of the value 0.2329. 
The cryogenic apparatus, essentially the same as that used by 
Weiss and Kamerlingh Osnes is shown in PI. I fig. 3 Once more 
we see the cover B, the adjusting tube f, and the holder b . The 
cover with its various parts: the cap with the stuffing-box D, glass 
tube C, window with plane parallel glass plate C\, the system B(, 
for adjusting the whole apparatus, the tension rods B, for supporting 
the Dewar tube, the helium thermometer 6, the little screens to 
protect the upper portions of the apparatus from cooling, etc is just 
the same as before. The Dewar tube is of the same shape, but the 
lower portion is of greater diameter. The only difference between 
the adjusting tube f and that which was used in the other invest,- 
gations is that the lower portion /,' is of greater diameter. 
