140 Mr. Hatchett’s Experiments on the various Alloys, 
the box, they were found to be sensibly diminished. This, like the 
experiments of the first set, was intended to show the compa- 
rative diminution of gold differently alloyed ; but, whereas that 
shewed the effect of rubbing only, this shewed the joint effect of 
rubbing and striking, and was intended to imitate (although in 
a more violent degree) the effect produced upon coin by pouring 
it out of one bag or drawer into another. 
The experiments of the third set were made by pressing the 
pieces to be examined against the rim of a flat horizontal wheel, 
by means of equal weights, so that, by turning the wheel round, 
they all suffered an equal degree of friction. That part of the 
wheel against which the pieces rubbed, was sprinkled or coated 
with some kind of powder, which was occasionally varied. 
The above statement will convey a general idea of the manner 
of making the experiments ; but, that the whole may be more 
fully comprehended, the following description of the instru- 
ments has been added by Mr. Cavendish.* 
DESCRIPTION OF THE INSTRUMENTS. 
It has been already observed that, in the first series of expe- 
riments, 28 pieces of coin were fixed to a frame, and that over 
each of them was placed another piece, which was pressed 
against it by a weight; and that these upper pieces were all 
connected to a second frame, so that, in consequence of the 
motion communicated thereto by cranks, each upper piece was 
rubbed backwards and forwards upon that which was under it. 
Fig. 3, (Plate II.) represents a plan of this instrument; and 
Fig. 2 is a vertical section of it, drawn parallel to the line AB. 
* The instruments were made by Mr. Cuthbertson, of Poland-street, who also 
had the care of them during the experiments which were made at his house. 
