experiments on Various alleys of gold. 3Q3 



By the help of the inftruments above defcribed, it was pro- Defcriptionof 

 pofed to determine, as accurately as poffible, dSSST *?t* 



lft. The comparative wear of foft and of hard gold. effeds of fric- 



2dly. Whether coins with flat or with raifed furfaces furTer tion ^ coil% 

 the greateft lofs by friction, when fubjedted to it under fimilar 

 circumftances*. 



It is fcarcely neceffary to obferve, that rigoroufly exact re- m 



fults could not be expe&ed in all the minutiae of experiments 

 like the prefent; for, many circumftances, apparently but 

 trivial, produced almoft unfurmountable obftacles ; but, never- 

 thelefs, thefe did not impede the effential objects from being 

 inveftigated, and determined, in a manner fufficiently fatisfae- 

 tory. 



Before the experiments are defcribed, it will be proper to 

 add, that, to obviate the irregular effects which would be pro- 

 duced by the inequality of the impreflions ufually employed for 

 coins, Mr. Cavendifli fuggefted a die, which was executed by 

 Mr. Pingo, and which confifted of round prominencies re- 

 gularly difpofed over the furface, fo that the effects which this 

 impreffion produced, during friction, were uniformly the fame 

 in every direction. 



The firft experiments were intended to afcertain the different 

 wear of gold made ftandard by various metals; and the pieces 

 were rubbed againft each other by meaus of the firft-defcribed 

 apparatus, which the author calls No. J. 



Some preparatory experiments were alfo made, to try the 

 effecls of this machine, as well as to determine, in fome mea- 

 fure, the comparative wear of gold made ftandard by copper, 

 of a mixture of gold and copper in equal proportions, and, 

 Iaftly, of copper. 



* Although coins with protuberances on their furfaces, have been 

 generally fuppofed to fuffer more by friction than thofe which are 

 flat, yet, as this opinion has been questioned, and as feveral objec- 

 tions have been made to it by intelligent perfons, it was thought 

 expedient that the decifion of the queftion mould form part of the 

 prefent inveftigation. 



(To be continued.) 



