Dr. TjTidall on the Laws of Magnetism. 271 



our magnet will show, that, even supposing M. Miiller^s objec- 

 tions to be well-grounded, they are not in the slightest degree 

 applicable at present. In all cases the tangent of the aforesaid 

 angle may be taken as the accurate expression of the magnetic 

 force. 



10. Table I. contains the results obtained during one of the 

 earliest trials of the new method of experiment. After balancing 

 the ball, a weight of 300 grammes was laid upon the scale-pan, the 

 rheostat being so arranged that very little wire was in the circuit. 

 The magnet was excited and the ball attracted. By turning the 

 handle of the rheostat, and thus slowly damping the current, a 

 point was at length attained where the ball gave way ; here the 

 turning of the handle ceased, and the angle was read off. The 

 rheostat was then turned backwards to its former position, a 

 weight of 10 grammes was added to the 300, and the same pro- 

 cess repeated. A series of equivalents for the magnetic attraction 

 was thus fomid, increasing by a common difference 10. The 

 angles and the weights corresponding to them are set side by side 

 in the foUomng table, the former being expressed in degrees and 

 decimals of a degree. 



11. To ascertain the ratio of the weight to the corresponding 

 magnetic force, the former ought, strictly speaking, to be divided 

 by tan /3 ; but for the angles which here appear, the tangents are 

 proportional to the arcs, and hence the latter are, in the present 

 instance, made use of as divisors. In all other tables throughout 

 this memoir the angles are expressed in degrees and minutes ; 

 and the tangents of the angles, instead of the arcs themselves, 

 are made use of. 



Table I. 



