131 



by nicking them across with a file, could be easily broken 

 into square pieces, whose corners could be taken off, and 

 rounded in the same manner. 



I do not repeat the other precautions to be observed m 

 this process, which have been aheady so well and saga- 

 ciously described by the Rev. Mr. Edwards: but the cir- 

 cumstances above-mentioned, a prudent attention to which 

 is, in my opinion, essentially necessary to the success of it, 

 are not to be collected from any directions published on 

 the subject that are known to me. And though particular 

 artists may, by large experience, arrive at a sufficient know- 

 ledge 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 any hands, being 

 the design of this essay, I thought it necessary, to state the 

 above particulars fully; though I 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 construction of the telescope, acquired 

 by Mr. Short, seems not to have been transmitted to any 



successor. 



I come now to speak of the most difficult part of the 

 mechanism of this instrument, that of communicating a 

 proper figure to the mirrors; on which depends the powers 

 of the telescope, when its dimensions are given: for the 

 manner of polishing them, to the highest degree of lustre, 

 has been already well understood and described. They who 

 have tried this part of the work, and know how incour 



ceivably 



