190 Proceedings of the Royal Society of Edinburgh. [Sess. 
of the needle to the solenoid. For general use, however, it is convenient 
to have the solenoid and coil on the same side. It is worthy of remark, in 
passing, that even if is placed as close up as possible to the end of the 
Fig. 4. 
solenoid, it can alter the field at the centre of the specimen by not so much 
as \ per cent. 
When used for testing specimens at temperatures higher than that of 
the room, an electric furnace of a type similar to that devised by Dr G. E. 
Allan,* is placed within the helix. In fig. 6 it is shown in position. A 
Fig. 5. 
tube E of unglazed porcelain of about the same length as the solenoid, 
having an internal diameter of 23*5 mm. and a thickness of about 2 mm., 
is wound non-inductively with fine platinum wire ; the ends of this wire 
are brought out to two terminals mounted on a slate frame at F. The tube 
* Phil. Mag., 1904, p. 46. 
