specific Gravity , and comparative JVear of Gold. 179 
Tl e whole motion of the pieces of coin, in the experiment of 
Table III. was about 687000 inches; while the whole motion 
of the pieces in the experiment of Table X. was only 62205. 
The weight by which the pieces were pressed was the same in 
both experiments* so that the pieces sustained eleven times more 
friction in the former than in the latter experiment. But it is 
worthv of notice, that the greater part of the different metals 
suffered the most considerable diminution by the last mode of 
examination ; and this may be regarded as an additional instance 
of the small diminution, which metal suffers by being rubbed 
against metal in a solid form, considered comparatively with 
that which it suffers when rubbed against the same metal in 
small particles. 
Moreover, it is remarkable, that although the diminution of 
all the metals which have been examined, excepting silver and 
copper, is less in the Illd than in the Xth Table, yet that of 
copper is many times greater. 
Mr. Cavendish, considering how necessary it was to deter- 
mine whether there is any material difference, in point of wear, 
between goid coin intirely of the same quality and that in 
which the gold is of different qualities, was induced to make the 
following Table of comparison, formed upon the results stated 
in Table V. 
A a 2 
