218 



Mr W. S. HARRIS on the Heat excited in 



19. This order, with the exception of tin, is about the same 

 as that already observed with the common electrical discharge *, 

 and was invariably shewn when the wires were placed in the 

 circuit, externally, as above described. It is, however, liable to 

 exceptions when deduced from the heating effects observed, by 

 including the metals in the electrometer ; hence, in applying 

 the principle arrived at by Mr CHILDREN, in the course of his 

 fine experiments with a battery of large plates, that the heat 

 evolved by the metal, whilst transmitting the charge, is in some 

 inverse ratio of the conducting power,' we must take into account 

 the circumstances already noticed (10), from which it appears 

 that the best conductors may appear occasionally to be the most 

 heated ; it is therefore only in employing charges within the 

 limit of the transmitting power that the above principle becomes 

 applicable. The following is an experimental illustration of this 

 with the metals, copper and platinum, when enclosed in the bulb 

 of the electrometer. 



TABLE VI. 



Thus, when the force is great, the best conductor is the most 



sure a good contact, the surfaces being clean and fair. The conducting powers were 

 ascertained according to the method described in section 12, exp.f. In this case, 

 the battery was provided with two additional contact cups ; with these the forcep- 

 wires above mentioned, were made to connect at pleasure by the intervention of cups 

 containing mercury in which they were secured, and sustained on pillars of glass, as 

 in m , Fig. 3. 



* Transactions of the Royal Society of London, for the year 1821, p. 488. 



