﻿Rate of E eolation of Heat by Orangite. 185 



not adding very greatly to the sensitiveness owing to the 

 increased resistance, lessens the importance of small thermal 

 effects at the galvanometer terminals. The resistance of the 

 couple is 71*2 ohms, that of the galvanometer 30*0 ohms. 

 As the thermo-electric power of the wires employed was 

 found to be 31*94 microvolts per degree at 0° C., and the 

 galvanometer is deflected on reversal 13*88 scale-divisions 

 per microvolt applied to its terminals, we find that the 

 , n . , . 1388 x 31-94x16x30-0 

 deflexion per degree is mw = ' 



scale-divisions. This figure is not needed in the determination 

 but is useful in showing the order of the temperature 

 differences involved. 



The heating-coil is of german-silver wire, silk-insulated 

 and wound on a thin copper rod. The coil just fits down 

 the tube in the centre of A, and being a little shorter than 

 the tube leaves a space about one centimetre long at the top, 

 which is plugged with cotton-wool. The heater current is 

 led in and out by flexible leads encased in rubber and copper 

 tabes similar to those employed for the couple leads. The 

 flexible leads terminate in the annular space between B and 

 C, where they are connected to a pair of single insulated 

 copper wires 0*195 mm. in diameter leading to the heating-coil. 

 This arrangement lessens the conduction oE heat along these 

 leads. The total resistance of the heater and leads at O 

 is about 129*5 ohms. In view of the extraordinary results 

 obtained this measurement was made several times so as to 

 preclude the possibility of any error. It is estimated that 

 the combined resistance of the flexible leads and the thin 

 copper wires joining them to the heater must be about 

 0*4 ohm so that the resistance of the heating-coil must be 

 about 129*1 ohms. The heater current is supplied by an 

 accumulator. In the first series of experiments a single cell 

 was used, its voltage being measured before and after each 

 period of use on a Crompton potentiometer. In the second 

 series two cells in series were employed, the voltage being 

 read daily on a Weston voltmeter. As the resistance in series 

 with the heater was never less than 2000 ohms the difference 

 between the *open circuit P.D. and the effective P.D. is 

 negligible. 



First Series of Experiments. 



The orangite was put into the vessel and the valve- plate 

 carefully soldered on. The vessel was then exhausted to a few 

 mm. pressure by means of a Gervk pump, the temperature 

 being kept between 65° and 75° G., and P 3 5 tubes being in- 

 serted between the pump and the vessel. Having been kept at 



