Magneto-Electricity, and Electro-magnetical Machines, 129 



ments, and instead of changing the torsion so as to obtain an 

 equal number of revokitions, I let the torsion remain constant and 

 changed the number of revolutions to produce equal deflection, 

 and found that to maintain a torsion of 62^*^, required sixty revo- 

 lutions per minute in one case and ninety in the other, which 

 being nearly in the inverse ratio of the deflecting forces, T inier- 

 red that the deflecting forces are as the number of reversals in a 

 given time. 



Explanation of the Figure, 

 n s. The electro-magnetical dipping-needle, fastened to an axis pivoted in the 

 two brass columns, E and F. 



A. Two copper circles or wheels, to which are soldered the two ends of the 

 coil which wraps n s. 



B. A block of ivory having two mercury grooves, in which play the two pairs 

 of semicircles of copper, C. 



D. The support of the ivory. 



N S. The semicircular magnet, supported by the wooden column, W. 



Vol. XXXIV.— No. 1. 17 



