C 495 ] 



telefcope defciibed, ibid. Boning rods, and their ufe, dcfcribcd, p. 412. Cup and 

 tripod for prefer ving the point upon the ground, where the meafurement was difcon- 

 tinued at nighr, and refumed next morning, p. 412. Difference between meafuring 

 with a rod of twenty feet, and with rods of twenty feet three inches, p. 412. Brafs 

 Clip iifed on thefe occalions defcnbed, p. 41^. ^i^. Nature of the tripod (tab. 

 XVIII.) exphiined, p. 413. Method of fufpending the plummet from any part of 

 the deal rods indifferently, p. 414. Wheels for terminating, in a permanent manner, 

 the extremities of the bafe, tab. XVIII. ibid. Mr. Mylne's improved machines for 

 certainly referring to the fame point on any occafion of correAing or repeating the 

 work (reprefented in tab. XVIII.), p. 415. Rough meafurement of the bafe with 

 the chain, and determination of the relative heights of the ftations by means of the 

 telefcopic fpirit level (tab. XVI. and XVII.), p. 416. The firft meafurement of the 

 fouth-eaft fedion of the bafe completed in three hours and a half, p. 417, 418. 

 The fame feftion re-meafured, wish the probable caufe of the variation, p. 418. 

 The operation with the chain fufpended, and why, p. 419. Defcription of a hold- 

 faft for the rear-end of the chain, invented by Col. Pringle (reprefented by two ele- 

 vations adjoining in tab. XVII.), ibid. The operations refumed by meafuring twice 

 with the chain forwards and back again the fecond fe£tion of the bafe, ibid. The 

 level of the iiril and fecond feftion of the bafe taken, with an account of the fpiiit- 

 level made ufe of, p. 420. The firft general table relating to the levels of the 

 bafe explained, ibid, p, 421. Col. Calderwood's method of computing the difference 

 between the hypothenufal diftances of 600 feet each, and the reduced bafe diflances, 

 p. 420. Tracing of the bafe with the tranfit inftrument, p. 421, 422. Confecjuenceof 

 delaying the ufe of that inftrument, p. 422. Levels of the third feftion taken, and 

 the rough meafurement thereof with the chain completed, p. 422, 423. Refult of the 

 examination of the length of the chain in different temperatures, p. 42:;. Defcenc 

 from the lower end of the bafe to the furface of the Thames at Hampton, p. 424. 

 Meafurement of the bafe with the deal rods, p. 425. Method of performing that 

 operation, p. 426. Difference of meafuring by coincidences and contacts accounted 

 for, p. 427. The two firft hypothenufes re-meafured, with the refult, p. 428. 

 Their Maiellies prevented by the weather from feeirg the nature of the operations, 

 p. 429. Method of difcovering the error of the chain at each ibtion, p. 429. In- 

 conveniences occurring from the humid and dry flate of the atmofphere, &c. p. 430. 

 See Expanjibiliiy. Different comparifons of the rods with the ftandard, and the 

 refult, p. 432, 433. Near agreement between the refult by the deal rods, and that 

 furnifhed by the rough meafurement with the chain, accounted for, p. 433. Mea* 

 furement with the deal rods finifhed, ibid. Expanfion of the deal rods, p. 

 434 — 436. See Riga Red-iuoodt Deal Rods. Mr. Ramfden's obfervations o£ 

 the ditierent expanfions, p. 435. Operations on Hounflow-Heath totally fuf- 

 pended, p. 438. Comparilon made in the beginning of September at Spring 

 Grove, when the rods were in their dry or contraiTied (late, and the remeafure- 



jnent 



