640 EEPORT— 1892. 



10. A Contribution to the Theori/ of the perfect Influence Machine. 



By J. Gray, B.Sc. 



The theory of the perfect influence machine has been shown by Clerk Maxwell 

 to be analogous to Oarnot's theory of the perfect heat-engine. Maxwell points 

 out there is a loss of energy in the ordinary influence machine through sparking at 

 the contacts, which would render the machine inefficient even though losses from 

 leakage and the like were completely done away with. Maxwell has described a 

 machine in which sparking and the loss due to it are eliminated. This is done by 

 causing the carrier of electricity always to make contact with charging and dis- 

 charging conductors when the former is at the same potential as the latter. In 

 the case of the discharging conductors this is done by prolonging the contact 

 springs to meet the carrier. In case of the charging conductors this is not sufficient ; 

 it is necessary to surround the end of their contact springs by two additional con- 

 ductors charged to an equal and opposite potential, and of such a capacity as will 

 just reduce to zero the potential of the small quantity of electricity left from the 

 previous discharge. These additional conductors were called by Maxwell regene- 

 rators, as being analogous to regenerators in the heat-engine. 



The object of the author is to investigate the efficiency of an influence machine 

 constructed according to Maxwell's design, and other designs less perfect. This is 

 done by drawing a QV (quantity-potential) energy diagram for one revolution of 



the carrier. The results obtained are as follows : — 



Theoretical efficiency 



Maxwell's machine 1 



without regenerators . 



without long contacts on receivers 

 without regenerators and without 

 long contacts on chargers , 



1 



1 + i^ 



Q 

 2 



1 



li+ei 



Ordinary machine with all contacts points . . ~ 



where a = quantity received or discharged by a carrier in each revolution. 



v = the potential (numerical value) of the positive or negative receiver. 



V = the potential of the residual charge to be reduced to zero by the regene- 

 rator. 



a = the part of the carrier's capacity due to its not being completely sur- 

 rounded by the discharging conductor. 



The conclusion is that the regenerators are of much less importance than the 

 long contacts in adding to the efficiency of an mfluence machine. 



SATURDAY, AUGUST 6. 



The following Papers and Reports were read : — 



Depaetmetti I. — Physics. 



1. Sources of Heat generated in the Galvanic Battery, 

 By Magnus Maclean, M.A., F.B.S.E. 



These experiments were suggested by a paper read by Lord Kelvin to the 

 British Association in Belfast in 1852, and reprinted in ' Mathematical and Physical 



