Improved Geometrical Plotting Quadrant, &c. 1 63 



3. The bowels were then relieved; and by taking off at 

 the same time local inflammation of the lungs, by a reduced 

 air being inhaled, and by medicines internally, being a cau- 

 tious application of bark, a speedy cure was accomplished. 



4. Query : Would any other means have saved this per- 

 son's life ? 



I have the honour to remain, dear sir, 



Your obliged devoted servant, 



Robert John Thornton. 



XXVI. Description of an improved Geometrical Plotting 

 Quadrant, Level, and Calculator, for the Use of Navi- 

 gation and Lund Surveying, ascertaining inaccessible Di- 

 stances ; and fur demonstrating and determining various 

 Problems in Geometry and Trigonometry. By Mr. Ro- 

 bert Salmon, of JVobum* . 



VJn the instrument and parts thereof are engraved the 

 names given by the inventor, and made use of in these ex- 

 planations ; the base line being that at right angles with the 

 yo degrees on the arch, as it is also to the perpendicular, 

 which perpendicular always moves parallel to the 90 degrees. 

 For the use of land surveying, where the instrument can be 

 made stationary, the sight (marked a, fig. 1. PI. IV.) with 

 the small hole in it must be applied ; but for sea service, the 

 one b, fig. 2. with the mirror, must be substituted in its 

 place. 



Every person who has had occasion to describe or calcu- 

 late the parts of the right-lined figures used in geometry, 

 perspective, surveying, navigation, dialing, architecture, &c. 

 &c. must have perceived that all of them are resolvable into 

 the most simple of figures — a triangle, or some number ot 

 them. 



Hence the great importance of geometry and trigonome- 



• From Transactions of the Society of Arts, &c. 1806. — -The silver medal of 

 the society, and ten guineas, were voted to Mr. Salmon for this communi- 

 cation. One of the instruments is preserved in the society's icpository, for 

 the inspection of the public. 



L 2 try, 



