234 M. W. Weber on the Measurement of Electric 



grammes. Of this 10 kilogrammes were used for the ring A, 

 which consisted of 145 windings; enclosing altogether a surface 

 of nearly 105 square metres. , This ring was placed vertically, 

 and by means of a winch could be rapidly rotated in a semi- 

 circle, so that the perpendicular upon the plane of the ring at 

 the commencement and at the end of the rotation coincided with 

 the magnetic meridian. The other 153 kilogrammes were used 

 for the ring B, which consisted of 1854 windings, giving toge- 

 ther a section 202 millims.in breadth, and 70*9 millims. in height: 

 the internal diameter of this ring was 303'51, and the external 

 374*41 millims. This second ring was firmly fixed, and its plane 

 coincided with that of the magnetic meridian. In the centre of 

 this second ring B, a small magnetic needle 60 millims. long, 

 provided with a mirror, was suspended by a filament of silk, as 

 in a small magnetometer; and the oscillations and deflections of 

 the needle were observed with a telescope, directed to the mirror, 

 on a scale about 4 metres from the mirror. 



The observations were made in the following manner. The 

 ring A was first so placed that its plane coincided with the 

 magnetic meridian, and the needle in the middle of the ring was 

 thereby brought to rest ; thereupon the ring A was suddenly 

 turned 90°. By this means the needle in the middle of the ring 

 was set in rotation, and by means of the telescope the position 

 of the needle was observed on the scale at its greatest (positive) 

 deflection after half an oscillation. After a complete oscillation, 

 and therefore an oscillation and a half after the beginning, the 

 needle attained its greatest deflection on the opposite side, which 

 was also observed on the scale. In the moment at which the 

 needle passed its original position of rest, and therefore two 

 oscillations after the beginning of the experiments, the ring A 

 was rotated 180°. The oscillating needle was thereby arrested 

 in the middle of its motion, and thrown backwards, upon which 

 its greatest negative and greatest positive deflectionswere observed 

 on the scale. After the expiration of four oscillations from the 

 commencement, that is, at the moment at which the needle 

 returning from its last deflection passed its original position of 

 rest, the ring was again turned forwards by 180°, and then the 

 same oscillation observed as in the first case, and in this manner 

 the experiments were continued until a sufficient series of obser- 

 vations was obtained. For each series, in the first column of 

 the following Table are given the deflections observed on the scale 

 and arranged in order under one another ; in the second column 

 the mean between two successive positive or negative deflec- 

 tions are added. In the third column are the differences of the 

 ni( ans referring to positive and negative deflection, that is, the 

 magnitude of the whole arc. 



