508 



Professor W. C. Moberts- Austen 



[Feb. 5, 



The ftrrangemeiit consists in inclosing a galvanometer of the Deprez and 

 d'Arsonval type iu a large camera ; a fixed mirror F, being placed below the 

 movable mirror M, of the galvanometer, so that the light from the lime cylimler 

 L, reflected in the mirror H, passes to both mirrors, F and M, and is reflected in 

 the direction of a fine horizontal slit A B, behind which a sensitised photographic 

 plate C, is drawn vertically past the slit by means of gearing, D, driven by clock- 

 work. The ray from the fixed mirror is interrupted periodically by the vane E, 



Fig. 4. 



and a beaded datum line is given, which enables any irregularity in the advance 

 of the plate to be detected. 



The amount of divergence from its datum line of the spot of light reflected 

 by the movable mirror at any given moment bears a relation (which can readily 

 be found by calibration) to the temperature to which the thermo- junction X, is 

 heated, and the variations of temperature are recorded by a curve which is the 

 resultant of the upward movement of the plate and the horizontal movement of 

 the spot of liy;ht. A crucible c, which may be filled with molten metal, is pro- 

 vided with a tubulure, T, for the insertion of the thermo-junction. The crucible 

 is suspended by wires in a double jacket of tin plate, a h. 



It will have been evident that the thermo-junction of platinum and 

 platinum-rhodium could not be used for measuring temperatures 

 higher than the melting-point of the platinum of which it is made. 

 Metals witli higher fusion-points than platinum are, however, avail- 



