ON TRANSIENT ELECTRIC CURRENTS. 339 



was clamped while the pointer of the twisting arm was at zero of the 

 graduated circle. Two clamps were previously fixed on both sides 

 of the twisting arm such that when the wire was twisted in either 

 direction, the arm should stop at the required angle of twist on either 

 side of the initial position of no torsion. The wire was twisted be- 

 tween two extreme limits of twist by pulling the strings attached to 

 the twisting arm in the way before mentioned. When the Avire was 

 first twisted, the deflection of the galvanometer magnet was generally 

 large, but after repeated twistings and untwistings, the current 

 settled to its ultimate value, and the reading was then noted. 



The coil of the low resistance ballistic galvanometer was wound 

 in 20 layers of thick copper wire. It had a resistance of 0.28 ohm. 

 In the core of the coil, a heavy magnet was suspended and the first 

 swing was read by the deflection of a spot of light reflected from a 

 mirror placed outside the coil, but rigidly connected with the magnet. 

 The suspension was similar to that of the ballistic galvanometer made 

 by Siemens and Halske. Since the logarithmic decrement of the 

 vibrating 1 magnet was very small, no correction arising from it was 

 thought necessary, so that the amount of current in the arbitrary 

 scale was taken to be equal to the reading of the first swing. As 

 the moment of the galvanometer magnet is liable to changes especially 

 when the momentary currents are passed through the galvanometer 

 coil, the galvanometer was gauged from time to time by mean- of an 

 earth inductor. 



The magnetizing coil was wound in six layers. The coil was 

 placed on a table due magnetic east and west, and at a distance of 

 nearly 5 metres from the ballistic galvanometer. It was 25 cm. 

 long, and had a resistance of 1.3 ohm. The magnetizing field due to 

 a current of one ampere was 35.5 C. G. S. units. The current was 

 derived from 16 Daniell cells, and its strength was measured by means 



