VOL. LXVI.] PHILOSOPHICAL TRANSACTIONS. 97 



and that a piece of iron, of about 5 dwts. which was tried by the smaller and 

 more accurate balance, weighed, as appeared by an index which moved opposite 

 to a quadrant, somewhat more when cold than when hot. Dr. R. tried the 

 same experiment on copper ; and found a piece of copper, of nearly lib. weight, 

 4 grains lighter after it had been left some hours to cool in the balance than 

 when it was put in. He repeated the experiment, and found the event the 

 same ; but suspecting this might possibly arise from the copper casting scales, 

 he placed a sheet of white paper under the balance, and collected as many 

 scales as made up nearly the deficiency of the weight. 



April '29, 1776, Dr. R. heated a cylinder of wrought iron, which weighed 

 55 lb. to a white heat, and exactly balanced the same, when hot, in the presence 

 of many members of then. s. After the cylinder had been 2 hours cooling in 

 the scale, he weighed it again, and found that it had increased in weight 3 dwts. 

 and a few grains Five hours after cooling, Mr. Magellan weighed it, and 

 found it had increased in weight 3 dwts. 1 7 grains. Six hours after cooling, 

 when the cylinder was blood-warm. Dr. R. weighed it again, and found it to 

 have increased in weight 4 dwts. The day following, about 2'2 hours after 

 cooling he again weighed it, and found that it had increased in weight 6 dwts. 17 

 grains. Mr. Abram Whitehouse, who was very solicitous to have the above ex- 

 periment made accurately, procured from Mr. Samuel Read a very exact beam, 

 which readily turned, to the conviction of all the above gentlemen, with less 

 than a pennyweight, though loaded with the above iron cylinder ; but Matthew 

 Raper, Andrew Crosby, Esquires, and Dr. R. examined the beam leisurely and 

 accurately, and found it turned very distinctly with 4 grains, though loaded as 

 above. In order to discover the cause of this increase of weight of the cylinder 

 when cold, Dr. R. heated 2 oz. 8 dwts. of the scales or calx of wrought iron, 

 and found the same to increase in weight 5 grains when cold. Dr. R. heated 2 

 pieces of pure silver which weighed 2 lb. 10 oz. 5 dwts. ; and when the silver 

 was cold it increased in weight 5 grains, though it produces no calx from being 

 heated red-hot. 



XXXII. Experiments and Observations on a New Apparatus, called, A Machine 

 for exhibiting perpetual Electricity. By Mr. JVilliam Henley, F. R. S. 

 p. 313. 



Mr. George Adams, philosophical instrument maker to his majesty, lately 

 showed to Mr. H. a little apparatus, which he called a machine for exhibiting 

 perpetual electricity, invented by Mr. Volta. This machine consisted of a cir- 

 cular plate of glass, about 8 inches in diameter, covered on one side with a coat- 

 ing of bees-wax and rosin, about the l6th part of an inch thick. This coat of 

 wax, &c. being strongly excited with a dry warm flannel, he placed on it a cir- 



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