238 DR. A. A RAMBAUT OR UNDERGROUND TEMPERATURE AT OXFORD 
On account of the differential character of the equation (a), (p. 242), the value of 
this coil does not concern us except in computing the correction for the temperature 
of the box, and then an approximate value only is required. 
The apparatus is provided with a slow motion contact-maker of Mr. Horace 
Darwin’s pattern, # and Griffiths’ thermo-electric key.f 
* ‘Nature, November 14, 1895, 
f ‘Phil. Trans.,’ A, vol, 184 (1893), pp. 397-8. 
Fig. 1.—Resistance Box and Galvanometer at the Radcliffo Observatory, Oxford. 
