45 
specific Gravity , and comparative Wear oj Gold. 
most by wear, under the various circumstances of friction to 
which coin is subjected in the course of circulation ? 
2dly. Whether coin with a flat, smooth, and broad surface, 
wears less than coin which has certain protuberant parts raised 
above the ground or general level of the pieces ? 
Concerning the first question, opinions were various, and the 
most intelligent persons were uncertain whether very soft or 
hard gold was to be preferred ; and, in respect to the second 
question, it must be observed, that although the prevalent opi- 
nion was in favour of flat and smooth surfaces, yet, as the fact 
had never been fully and satisfactorily determined, this oppor- 
tunity was embraced, in order that every doubt might be 
removed. 
The great value of the material, had hitherto prevented pri- 
vate individuals from ascertaining these facts by experiment; 
and, as a public concern, this subject of investigation, although 
so important to political economy and to science, does not appear 
to have been noticed by any European government, until the 
Right Honourable and enlightened Members of the abovemen- 
tioned Committee proposed the inquiry, and furnished the re- 
quisite means for making the experiments.* 
At the request of Mr. Cavendish, I have written the follow- 
ing account; but I should be highly unjust and ungrateful to 
that gentleman, did I not here publicly acknowledge how great 
a portion truly belongs to him, of any merit which these expe- 
riments may be found to possess : for, at all times, I was favoured 
with his valuable advice; and the machines to produce friction, 
as well as the dies, were entirely contrived by himself. At the 
* These experiments were begun in the latter end of 1798, and were completed in 
April, 1801, 
