Meofurement of a Bofe on HounPiOw Heath. 41 j 



found to be within a few inches of the picket correfponding 

 with the hypothenufe, ns determined by the chain. But with 

 the rods of twenty feet three inches, the day's work was al- 

 ways ended with a fractional rod, by fufpending a plummet 

 from fome convenient part of the ftem, marked for the pur- 

 pofe, and which confequently became the point of commence- 



ment next mornmg. 



The brafs cup, made ufe of on thefe occafions, is of the 

 figure of an inverted truncated cone, whofe mean diameter is 

 four Inches, and Its depth about five, with a very fm all incli- 

 nation in the fides. It was placed in a hole dug for it in the 

 earth, immediately under the point of fufpenfion of the plum- 

 met, ferving only to hold the water in which it vibrated. 



The nature of the tripod will be heft conceived from the 

 plan and elevation of It in tab. XVllI. It confifls of two 

 flrong pieces of beech wood, mortoifed into each other, fo as 

 to lefemble a half crofs, or the letter T inverted, having three 

 ftrong iron prongs, about twelve" inches in length, which pafs 

 through the ends of the wood, and are faftened to it by fquare 

 nuts at top. On the furface of the tripod lies a fimilar half 

 crofs of mahogany, moveable by means of grooves in the di- 

 redion of the longefl fide, and fixable by its proper fcrevvs, 

 when brought to the defired pofition. This mahogany half- 

 crofs carries on its furface a brafs ruler, moveable at right-angle? 

 to the former dire6lion, fixable alfo by means of its own 

 fcrev^'S, and on whofe end is cut a very fine interfe<flion." 

 Thus any day's operation having been finilhed, the tripod was 

 placed near the cup, with it longed fide parallel to the line of 

 meafurement, and its prongs driven into the ground, fo as to 

 be rendered perfeClly immoveable without great violence. The 

 plummet being then fjfpended by a fine gilt wire, at any part 



of 



