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F, F, are fitted on the tube so as to bring the axis of the specimen into 
coincidence with that of the solenoid. A third bung F or a pad of cotton- 
wool is used to prevent access of warm air into the interior of the solenoid, 
and a covering of cotton-wool on the portion C D prevents it from warming 
up and conducting heat to the specimen. Instead of closing the glass tube 
at B, a cork may be used to stop up the opening, The cork, however, if 
dry, is liable to loosen and permit the liquid air to leak out, or if it is at all 
damp it expands and fractures the tube. 
Where tests have to be made as the specimen slowly warms up from 
the temperature of liquid air a Dewar tube is used, with its mouth closed 
by a cork which has two bent tubes passed through it — one for pouring in 
the liquid air, and the other for the bringing out of the leads from one or 
more thermo-elements in contact with the specimen. 
The dimensions given above for the internal diameter of the solenoid 
will be found sufficient for receiving a double vacuum Dewar tube for tests 
at — 252° C. on specimens immersed in liquid hydrogen. 
A slightly modified form of the stand supporting the solenoid permits 
of the latter being carried in an east and west position on one of the arms 
of the cross-piece of the magnetometer. The apparatus is therefore avail- 
able for use with specimens in either the “ A ” or “ B ” position of Gauss ; 
the methods described in Gray’s Absolute Measurements in Electricity and 
Magnetism for the determination of the effective lengths of the specimens 
thus become available. 
The considerable height of the magnetometer needle above the level of 
the magnetometer base-board (18 cm.) would also permit the apparatus to 
be readily adapted for testing by the “ one-pole ” method.* 
Several instruments of the above type have been built in the Physical 
Institute of the University of Glasgow, and are giving every satisfaction. 
* See Ewing’s Magnetic Induction in Iron and other Metals , p. 39. 
( Issued separately April 17, 1909.) 
