10 The Rev. T. R. Robinson on the Relation between the Temperature of 



easily made air-tight by Whitworth's scraping process. Two apertures glazed 

 with strong plate glass enabled me to read the index and inspect the wire ; 

 and an insulated wire passing through the top, and dipping in a mercury cup 

 formed in the binding-screw a, connected it with the battery. The box was 

 connected by a screw with the air-pump, which, however, was at the time not 

 in aood order. The following results are also each a mean of ten : 



The currents required to produce a given temperature are less, but the 

 resistance is the same ; its increase is therefore not due to any intrinsic quality 

 of the current. 



On attempting to pass the current of six Groves the wire gave way. 



Another piece was substituted, to try whether feeble currents were simi- 

 larly resisted, its diameter being j^. On passing a current 0.279, the lowest 

 which the actual position of the rheometer permitted me to measure, the wire 

 was heated 24°, and its resistance =189.4. Increasing the current to 0.315, 

 the wire was heated 9° more, and the resistance became 195.4. In fact, I be- 

 lieve it is impossible to pass any current whatever without changing the resist- 

 ance in some degree ; and think it highly probable, that this has given rise to 

 the opinion entertained by some philosophers, that the resistance is a function 

 of the current. 



This wire failed also in an attempt to obtain higher temperatures,* and was 



• In the first trial the zero of pyrometer was, before contact, -7.2 ; P'= 148.8 ; zero after, 

 + 25.2. If the whole of the lengthening took place during the cooling, P= 159-9 and r=2981.3. 

 The resistance = 967.1. In a second trial with an additional resistance of 50 in circuit, zero 



