142 Specula . 
whose corners could be taken off, and rounded in the 
same manner. 
I do not repeat the other precautions to be observed in 
this process, which have been already so well and saga- 
ciously described by the Rev. Mr. Edwards ; but the 
circumstances above mentioned, a prudent attention to 
which is in my opinion essentially necessary to the suc- 
cess of it, are not to be collected from any directions pub- 
lished on the subject that are known to me. And though 
particular artists may, by large experience, arrive at a 
sufficient knowledge in this matter for their own practice ; 
yet, to render that knowledge general, and to contribute 
as far as I could to the improvement of this instrument in 
in any hands, being the design of this essay, I thought it 
necessary to state the above particulars fully ; though 1 
doubt not that these, as well as other matters of moment 
in the operation, are known to many who chuse not to 
make them public. Thus the great skill in the construc- 
tion of the telescope, acquired by Mr. Short, seems not to 
have been transmitted to any successor. 
16 JYich . Jour . 30a 
I do not insert the rest of this valuable paper, because 
it relates merely to the method of grinding the specula ; 
those who are interested in the construction of optic glas- 
ses, will do well to refer to it. I have made Edward’s 
speculum metal, and with a small proportion of silver in 
it, I think it would be applicable to many other purposes* 
The polish and the colour are excellent. 
In the report of Elias Boudinot, Esq. on the mint 1796, 
1797, it is said that the beauty of gold coin is improved 
by making the alloy two thirds copper, and one third sil- 
ver. 
“ Copper precipitated by Tin. An intelligent corres- 
pondent, Mr. Collard of Birmingham, the proprietor of 
