H2 PERSPECTIVE INSTRUMENT. 



Inftrument for another, which feeras to unite the accuracy of the firft of thofe 

 SSsX'nf illftruments w 'th the fimplicity and portability of the fecond. 

 nature, As I conceive it may be of fome fervice to thofe who are in 



the habit of iketching landfcape, I fend you a defcription of 

 one which I have had made, that you may, if you think pro- 

 per, publiQi it in your Journal. Let A B, Fig. II. Plate 5. 

 be a flat rule, fuppofe twelve inches long, having at its ex- 

 tremities two arms B D and AF turning upon a joint at Band 

 A; and in each arm a circular joint at C and G: let the length 

 of each arm B D and A F be ten inches: a handle to fix on E, 

 and a thread patting through two holes equidiftant from the 

 handle, making any length, according to the angle under 

 which the view may be befl feen. 



To ufe the inftrument, take the end of the thread in the 

 mouth, and hold the inftrument upright before the eye, then 

 move either or both of the arms till the points D and F are 

 brought in a line between the eye and any point in the land- 

 fcape you may with to delineate; lay the inftrument upon the 

 drawing paper, and you will have the true fituation of fuch 

 part of the fubjecl. — Proceed in like manner, taking care al- 

 ways to keep the bafe line in the fame place, till you get as 

 many points as you require, by which means any landfcape or 

 building may be drawn very expeditioufly, and with a great 

 degree of accuracy. 



To make the inltrument as portable as pofiible, there is a 

 joint in A B, which the handle covers, and the pieces D G 

 and C F are made of thin brafs, to fold into the pieces A C 

 and BG; fo that the inftrument, when folded up, need oc- 

 cupy no more room in the pocket than a fmall fpeclacle cafe. 



It is perhaps unneceflary to add that this inftrument may be 

 ufed for the purpofe of copying, and anfwers the purpofe of 

 a triangular or quadrangular compafs. 

 I am, Sir, 

 Your mod obedient and humble fervanr, 



T. C. B. 



If the rough inclofed fketch of the inftrument is not fuffi- 

 ciently intelligible, Mr. Nicholfon may fee one at Mr. Frazer's, 

 Optician., in Bond-Street. 



Obfcrvations 



