VOL. LXXXVIII.] PHILOSOPHICAL TRANSACTIONS. 3Q5 



position, would acquire polarity in the same direction, and would attract the balls ; 

 but when the weights were moved to the contrary position, that pole which before 

 pointed to the north, would point to the south, and would repell the ball it was 

 approached to ; but yet, as repelling one ball towards the south has the same effect 

 on the arm as attracting the other towards the north, this would have no effect on 

 the position of the arm. After some time however, the poles of the weight would 

 be reversed, and would begin to attract the balls, and would therefore produce the 

 same kind of effect as was actually observed. 



To try whether this was the case, I detached the weights from the upper part of 

 the copper rods by which they were suspended, but still retained the lower joint, 

 namely, that which passed through them ; I then fixed them in their positive po- 

 sition, in such manner, that they could turn round on this joint, as a vertical axis. 

 I also made an apparatus, by which I could turn them half way round, on these 

 vertical axes, without opening the door of the room. Having suffered the appa- 

 ratus to remain in this manner for a day, I next morning observed the arm, and 

 having found it to be stationary, turned the weights half way round on their axes, 

 but could not perceive any motion in the arm. Having suffered the weights to 

 remain in this position for about an hour, I turned them back into their former 

 position, but without its having any effect on the arm. This experiment was re- 

 peated on 2 other days, with the same result. We may be sure, therefore, that 

 the effect in question could not be produced by magnetism in the weights ; for if it 

 was, turning them half round on their axes would immediately have changed their 

 magnetic attraction into repulsion, and have produced a motion in the arm. As 

 a further proof of this, I took off the leaden weights, and in their room placed 

 two 10-inch magnets ; the apparatus for turning them round being left as it was, 

 and the magnets being placed horizontal, and pointing to the balls, and with their 

 north poles turned to the north ; but I could not find that any alteration was pro- 

 duced in the place of the arm, by turning them half round : which not only confirms 

 the deduction drawn from the former experiment, but also seems to show, that in 

 the experiments with the iron rods, the effect produced could not be owing to 

 magnetism. 



The next thing which suggested itself to me was, that possibly the effect might 

 be owing to a difference of temperature between the weights and the case ; for it is 

 evident, that if the weights were much warmer than the case, they would warm 

 that side which was next to them, and produce a current of air, which would make 

 the balls approach nearer to the weights. Though I thought it not likely that 

 there should be sufficient difference, between the heat of the weights and case, to 

 have any sensible effect, and though it seemed improbable that, in all the fore- 

 going experiments, the weights should happen to be warmer than the case, I re- 

 solved to examine into it, and for this purpose removed the apparatus used in the 

 last experiments, and supported the weights by the copper rods, as before ; and 



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