5(56 I'HILOSOPHICAL TRANSACTIONS, [aNNO 1732. 



east in about 5 minutes, between the moon and the zenith, and to the south- 

 ward of Spica Virginis. It carried a stream of light after it about 40° long, and 

 1° or 1-1-° broad ; the brightness of the moon outshone the comet as it came 

 near her. 



Two Experiments on the Friction of Pulleys. By the Rev. J. T. Desriguliers, 

 LL. D. F. R. S. N° 425, p. 394. 



The first experiment was made with a tackle of 5 brass sheevers in iron 

 frames or blocks; that is, 3 sheevers in the upper block, and 2 in the lower. 

 The sheevers were 5 inches diameter, the pins half an inch, and the rope three 

 quarters. Having made an equilibrium, by hanging one hundred and a quarter 

 at the lower block, and a quarter of a hundred at the running rope ; he added 

 \7\ pounds before the power could go down and raise the weight. 



Exper. 2. — Two hundred and a half being balanced by half a hundred, the 

 addition of 28lb. made the power raise the weight. 



In the experiment 174- pounds exceeds by 44- pounds the sum of the frictions 

 deduced from the theory. But in the second experiment 28 pounds exceeds 

 the sum of the friction but 1 pound. 



The reason of this appeared to be, that the rope at first was too large for the 

 cheeks that held the sheevers ; but in the second experiment, where the rope 

 was more stretched, it was somewhat diminished in diameter, and so brought 

 off from rubbing so hard against the cheeks. 



F>om knowing the quantity of friction a priori, in such large tackles, we may 

 know what to expect in practice: for if one man, who for a small time can exert 

 the force of JOO pounds, thinks that he may draw up a stone, or a roll of 

 sheet-lead, or any other such weight, to the top of a house, with a tackle of 5, 

 because this would seem feasible from mechanical principles, will find himself 

 mistaken, on account of the friction, which will not be surmounted without an 

 additional force of 50 pounds. 



Further Experiments concerning Electricity. By Mr. Stephen Gray, F. R. S. 

 N° 426, p. 397. 



About the latter end of August, 1732, being at Mr. Wheler's, after having 

 repeated the experiment of making sulphur attract leaf-brass in vacuo, they 

 suspended from the top of a receiver, which was first exhausted of air, a white 

 thread, that hung down to about the middle of it. Then the receiver being 

 well rubbed, the thread was attracted by it vigorously. When it was at rest, 

 and hung perpendicular, the tube was rubbed, and being held near the receiver, 



