a little wooden case to defend it from 

 the wind. 



"As no more force is required to make 

 this arm turn round on its centre than 

 what is necessary to twist the suspending 

 wire, it is plain that if the wire is suffi- 

 ciently slender, the most minute force, 

 such as the attraction of a leaden weight 

 a few inches in diameter, will be sufficient 

 to draw the arm sensibly aside. The 

 weights which Mr Michell intended to 

 use were 8 inches in diameter. One of 

 these was to be placed on one side of the 

 case opposite to one of the balls, and as 

 near it as could conveniently be done, and 

 the other on the other side, opposite to 

 the other ball, so that the attraction of 

 both these weights would conspire in 

 drawing the arm aside ; and, when its 

 position, as affected by these weights, 

 was ascertained, the weights were to be 

 removed to the other side of the case, so 

 as to draw the arm the contrary way, and 

 the position of the arm was to be again 

 86 



