540 PHILOSOPHICAL TRANSACTIONS. [aNNO 1732. 



Dr. D. has shown by experiment, that when the weight is unknown, ^ of tlie 

 power is the friction of a cylinder whose surface moves as fast as the power, and 

 whose gudgeons are equal in diameter to the cylinder. Now as the diameter of 

 tiie first pulley is 8 times that of its pin, its friction must be 8 ounces. 



The second pulley, whose surface moves as slow again as the power, and 

 whose pin is 6 times less in diameter, must of consequence have its friction of 

 only 5i ounces; because 64 -^ 12 = 5i. 



The third pulley moving with i of the velocity of the power, on a pin of -J- 

 of its diameter, has for its friction 4^ oz. because 64 -^ 15 := 4^. 



Now the sum of all these frictions being 17.6 oz. which is the 5.4 part of 

 the power 61b. ; this addition so increases the friction, as to require a super- 

 addition of the 5.4 part of that first addition, and so on, in this series, 

 J7.62 + 3.2 + 0.59 &c. = 21.41 oz. 



Then the sum of the frictions on account of bending the ropes, deduced 

 from the experiment that a rope of -^ inch in diameter, stretched by 61b. re- 

 quires 4.5 oz. to bend it round a cylinder of 1 inch, amounts to 1.8 -|- 1.15 -f- 

 1.124 = 4.424 oz.; which with the otiier friction, amounts to 25.834 oz. But 

 as he had formerly shown in the Trans, that when a rope drawn by unequal 

 weight runs over a pulley, the pressure on the pin is diminished ; that dimi- 

 nished pressure, found by calculation to be near 6 oz. being taken from the 

 above sum, the friction remaining will be 1 9.834 oz. ; and the experiment is 

 just 20 oz. 



Nothing was here allowed for the weight added to bend the ropes, which 

 would still bring the experiment nearer the theory. 



j4 Way of Communicating the Magnetical Virtue to Iron and Steel, without the 

 help of a Loadstone. By M. Jrnold Marcel. N" 423, p. 294. 



In 1722, M. Marcel observed, that a long heavy bar of iron being set up- 

 right, and some filings of iron, or a bit of iron -wire laid on its upper end, those 

 filings or bit of wire would stick to another piece of bright pointed iron, and 

 suffer itself to be lifted up from the standing bar, even to the height of 5 

 inches. 



In 1726, making several more observations about the magnetical force, which 

 he found in large pieces of iron, he made use of a large iron vice, about golb. 

 weight, in which he fixed a small anvil of about 12lb. On the bright surface 

 of this anvil he laid the steel, to which he would communicate the virtue, in a 

 position north and south, which happened to be in a diagonal of the square sur- 

 face of the anvil. He then took a piece of iron, an inch square, and 33 inches 

 long, of about 8 lb. weight, having at one end the figure represented fig. 2, 



