FI. E. Nipher—The Electric Light. 141 
Art. XX.—The Electric Light ; by F. E. Nrpumr. 
In the Philosophical Magazine for January, 1879, p. 30, Mr. 
H. Preece gives a discussion, in which he shows the condi- 
tion to be supplied in electric lighting, in order to obtain a 
maximum effect. In eq. 2, p. 31, he gives for the heat dis- 
tributed to the incandescent material, 
E*7 
B= (+r+0) 
where p represents the battery resistance, and r and / represent 
the resistances of the connecting wires and an incandescent 
lamp, respectively. 
or m lamps joined up in series, we must substitute ni for J, 
while if joined in multiple arc, we must put - for’ In either 
case, the value of H is found to be a maximum, when the re- 
sistance of the lamp system is equal to that of the rest of the 
circuit. 
_ Mr. Preece then proceeds on the assumption that this condi- 
ion cannot be complied with, if n is large, reaching the conclu- 
sion that the amount of heat liberated in each lamp, varies in- 
versely as the square of the number of lamps. This is true in 
either of the two cases discussed by him. 
_ If, however, we have n lamps, arranged in n’ parallel circuits, 
im each of which we have n” lamps, the previous equation be- 
comes 
tr 
age | 
n 
gh ni! 
A haa, 
With this arrangement it is always possible to supply the 
Condition which makes H’”a maximum, entirely irrespective of 
the value of n. If 
n" 
p + | mg Z 
we shall have 
FE 
H’”’ = 
4(p+7r) 
" the total heat in n lamps is independent of the number of 
amps, 
e heat generated in each lamp will then vary inversely as 
the number of lamps. 
St. Louis, Dec. 30, 1879. 
