1908-9.] An Improved Form of Magnetometer. 
191 
is enclosed in a tube G of Jena glass, which fits as a cartridge within the 
magnetising solenoid. The space H H between the glass and porcelain 
tubes is packed with dry kaolin clay, which performs the double duty of 
supporting the furnace and preventing the coils of the platinum wire from 
changing their positions when expanded by heat. A cylinder of electrolytic 
D 
sheet-copper is placed within the tube E, and assists in maintaining a very 
uniform temperature over the space occupied by the specimens. 
In the figure the platinum wire is shown equally spaced over the porcelain 
tube. In reality this is far from being the case. The proper winding of 
the tube is an exceedingly troublesome operation, and can only be accom- 
plished by repeated trial. 
I 
m 
Fig. 7. 
0 
c 
The temperature of the furnace is measured b}^ means of the ordinary 
thermo-element or a platinum resistance thermometer. The two wooden 
stands used for the pyrometer are shown in position in figs. 4 and 5. As 
will be seen at once, the several slots in the horizontal carrier for fitting on 
the tops of the stands permit of these latter being placed clear of the sliding 
bases of the compensating coils. 
For tests at the temperature of liquid air the arrangement shown in 
fig. 7 is employed. The specimen A is enclosed in a glass tube BCD, of 
which the end B is closed and the end D is open and bent up. Cork bungs 
