1884.] measurement of the capacity of a condenser. 179 



with the standard fork (whose frequency was determined by Lord 

 Rayleigh) by counting the beats between the two. A resonator 

 being used, this could be very conveniently and accurately done. 



To compare the " 32" or the [32J and the " 64" forks both were 

 set vibrating, and the dipper carried by the latter was viewed over 

 the top of the former. A screen was brought down in front of 

 the prong of the fork over which we looked so that we could only 

 see the dipper between the screen and the prong when the latter 

 was very near its lowest position. 



A narrow horizontal slit ruled on a plate of smoked glass was 

 sometimes used instead of a screen. The dipper was thus seen 

 in a state of slow vibration, and by placing behind it a piece of 

 paper with a line ruled on it, which was just reached by the dipper 

 in its highest position, the vibrations could be very accurately 

 counted even when extremely slow. 



The following is a specimen of the electromagnetic observa- 

 tions. The extreme columns give the resistance (c) in b.a. units, 

 and the equilibrium position of the left edge of the band of light 

 on the scale when the currents are passing through the galvano- 

 meter. We write c. x for the capacity of the condenser marked "1. 



August VMh. 



522 56 



