2()8 EXPERIMENTS ON VARIOUS ALLOYS OF COLD,' 



many pieces in a In the fecond feries, 200 pieces of gold, differently alloyed, 

 box * were inclofed in a wooden box, of a cubic figure, which was 



kept conftantly turning round, till, by the repeated rubbing 

 and ftriking of the pieces againft each other, and againft the 

 iides of the box, they were found to be fenfibly diminished. 

 This, like the experiments of the firft fet, was intended to 

 fhow the comparative diminution of gold differently alloyed j 

 1 but, whereas that (hewed the effect of rubbing only, this 

 fhewed the joint effect of rubbing and ftriking, and was in- 

 tended to imitate (although in a more violent degree) the ef- 

 fect produced upon coin by pouring it out of one bag or 

 drawer into another. 

 Coin rubbed on a The experiments of the third fet were made by preffing the 

 flat furface. pieces to be examined againft the rim of a flat horizontal wheel, 

 by means of equal weights, fo that, by turning the wheel round, 

 they all fuffered an equal degree of friction. That part of the 

 wheel againft which the pieces rubbed, was fprinkled or coated 

 w ith fome kind of powder, which was occafionally varied. 



The above ftatement will convey a general idea of the man- 

 ner of making the experiments ; but, that the whole may be 

 more fully comprehended, the following defcription of the in- 

 ftruments has been added by Mr. Cavendiih.* 



DESCRIPTION OF THE INSTRUMENTS. 



Defcription of ^ n tne ^ r ^ feries of experiments, 28 pieces of coin were 

 machinery for fixed to a frame, and over each of them was placed another 



eSofffic- 6 P iece > which was P re(red a § ainfl k by a weight; and thefe 

 tion on coin. upper pieces were all connected to a fecond frame, fo that, in 



confequence of the motion communicated thereto by cranks, 



each upper piece was rubbed backwards and forwards upon 



that which was under it. 



Fig. 1, (Plate XIV.) reprefents a plan of this intlrument ; 



and Fig. 2 is a vertical lection of it, drawn parallel to the 



line AB. 



The upper frame, or that to which the upper pieces of coin 



are connected, is of brafs, and confifts of four bars, Fig. 1, 



AB, B6, ba, and aA, with three crofs bars Cc, Cc, Cc. 



, * The inftruments were made by Mr. Cuthbertfon, of Poland- 



ftreet, who alfo had the care of them during the experiments which 

 were made at his houfe. 



The 



