396 PHILOSOPHICAL TRANSACTIONS. [ANNO 1798. 



having placed them in the midway position, I put a lamp under each, and placed a 

 thermometer with its ball close to the outside of the case, near that part which 

 one of the weights approached to in its positive position, and in such manner that 

 I could distinguish the divisions by the telescope. Having done this, I shut the 

 door, and some time after moved the weights to the positive position. At first, 

 the arm was drawn aside only in its usual manner ; but in half an hour the effect 

 was so much increased, that the arm was drawn 14 divisions aside, instead of about 

 3, as it would otherwise have been, and the thermometer was raised near 14 ; 

 namely, from 6)° to 624- . On opening the door, the weights were found to be no 

 more heated, than just to prevent their feeling cool to my fingers. 



As the effect of a difference of temperature appeared to be so great, I bored a 

 small hole in one of the weights, about -§• of an inch deep, and inserted the ball of 

 a small thermometer, and then covered up the opening with cement. Another 

 small thermometer was placed with its ball close to the case, and as near to that 

 part to which the weight was approached as could be done with safety ; the ther- 

 mometers being so placed, that when the weights were in the negative position, 

 both could be seen through one of the telescopes, by means of light reflected from 

 a concave mirror. Three other experiments were then made with this apparatus, 

 viz. exper. 6 on Sept. 6, exper. 7 on Sept. 1 8, and exper 8 on Sept. 23 ; the results 

 of which were as follow : viz. 



Sept. 6. Motion of arm on moving weights from midway to — = 3.03 



— to + = 5.9 

 Sept. 18. Motion of arm on moving weights from midway to — =3.15 



— to+ =6.1 

 Sept. 23. Motion of arm on moving weights from midway to — = 3.13 



— to -f- = 5.72 



In these 3 experiments, the effect of the weight appeared to increase from 2 to 

 5-10ths of a division, on standing an hour; and the thermometers showed, that 

 the weights were 3 or 5-10ths of a degree warmer than the air close to the case. 

 In the last 2 experiments, I put a lamp into the room, over night, in hopes of 

 making the air warmer than the weights, but without effect, as the heat of the 

 weights exceeded that of the air more in these 2 experiments than in the former. 



On the evening of October 17, the weights being placed in the midway position, 

 lamps were put under them in order to warm them ; the door was then shut, and 

 the lamps suffered to burn out. The next morning it was found, on moving the 

 weights to the negative position, that they were 71° warmer than the air near the 

 case. After they had continued an hour in that position, they were found to have 

 cooled l-£°, so as to be only 6° warmer than the air. They were then moved to 

 the positive position ; and in both positions the arm was drawn aside about 4 di- 

 visions more, after the weights had remained an hour in that position, than it was 

 at first. 



