88 8 
Tools of Stone 'Wave. 
grounds, and a number of operations that require unex- 
pensive friction, these stone-ware graters, if I may so 
call them, as not being of the exact shape of tiles, may 
ultimately become very useful. I take a pleasure in fur- 
nishing you with a description of my method of applying 
this substance, accompanied with a specimen or two of a 
portable size, that you may the better be able to judge of 
their value to the arts, which to me the more I reflect on 
them seem the more important; as, in all operations of 
grinding a great deal of manual labour must first be 
bestowed on the tool, whereas here we may mould ours 
in an instant, if we use a press, as in pipe making, and 
the expense is infinitely inferior to that incurred in con- 
structing even the cheapest file or logrator. I am, &c. 
G. Cumberland. 
To Mr. Nicholson. 
Bristol , February 10, 1809. 
P. S. I have not yet tried it, not having the means just 
now at hand, but if a good parabolic reflector were to be 
impressed with a mass of stone-ware clay covered with 
muslin, so as to make several casts of different degrees of 
fineness, we might this way acquire tools, that would 
greatly lessen the expense of the operation of grinding; 
but much would depend on care in baking. Our stone 
ware warps but little ever. 
Annotation. 
This ingenious invention promises to be of considera- 
ble use in the arts. The abrasion of surfaces is perform- 
ed either by a toothed tool, as in filing, rasping, &c. or 
by a grinder, in which cutting or hard particles are bed- 
ded with considerable firmness in a softer mass ; or by 
scouring, polishing, &c. in which hard particles are more 
or less slightly retained in a soft or tenacious substance. 
