474 
PROFESSOR CLERK MAXWELL OX THE ELECTROMAGNETIC FIELD. 
the current, and the impulse it gives to the suspended coil of Weber’s dynamometer, 
depend on the square of the current at every instant during the short time it lasts. 
Hence we must obtain the solution of the equations, and from the solution we may find 
the effects both on the galvanometer and dynamometer ; and we may then make use of 
the method of Weber for estimating the intensity and duration of a current uniform 
while it lasts which would produce the same effects. 
(39) Let w 1? n 2 be the roots of the equation 
(LN-M> 2 + (RN+LS>+RS=0, (16) 
and let the primary coil be acted on by a constant electromotive force Rc, so that c is 
the constant current it could maintain ; then the complete solution of the equations for 
making contact is 
» c n \ n i 
S n l — n 2 
G 
-+NW 
+N e^+S- 
(17) 
cM 
s=-w 
{e^-e^} (18) 
From these we obtain for calculating the impulse on the dynamometer, 
j 'a*dt= 
hf dt = 
2 J / 3. _ 1 iyi 
{ 2 R — 2 rn+LS 
21 M 2 R 
Cs S(RN + LS)’ 
(19) 
( 20 ) 
The effects of the current in the secondary coil on the galvanometer and dynamometer 
are the same as those of a uniform current 
1 „ MR 
2 C RN + LS 
(40) The equation between work and energy may be easily verified. The work done 
by the electromotive force is 
%§xdt=c-(R,t—L). 
Work done in overcoming resistance and producing heat, 
R j# 2 <ft + Sjy = c 2 (R£ — f L). 
Energy remaining in the system, 
=ic 2 L. 
(41) If the circuit R is suddenly and completely interrupted while carrying a current 
c, then the equation of the current in the secondary coil would be 
M », 
y=c-e » . 
This current begins with a value c ^ , and gradually disappears. 
