Meafuremeni of a Bafe on Hon nilow- Heath, 44Q 



raethod, between the pohit of a micrometer fcrew, fupplylng 

 the place of the firft cock, and the fecond) the ivory mterfecuou 

 was at firft neceffarlly carried beyond the diamond line, foas to 

 make the intermediate fpace lefs than it (liould be, until by the 

 gradual grinding down of the moveable bell-metal button, it 

 was enlarged to twenty feet, as then fnewn by the accurate 

 coincidence of the interfection with the diamond line. 



It was by thefe diflances In tlie great plank, prolonged to 

 twenty- five feet, that the new length of the fteel chain was 

 •now fettled, fo as to obtain the full one hundred feet at four 

 meafurements. At this time too, brafs points were introduced 

 into the chain at every twenty-five feet, whereby its extent may 

 be compared on any future occafion; but the temperature had 

 now fallen to 66°i. 



Dljpojition of the Stands for the double 7neafurement with the 

 Chain and Glafs Rods ; defcription of the apparatus then applied 

 to the ends of the Chain ; and ultimate continuation of the 

 meafurement with the Glafs Rods alone. Tab. XVH. and 

 XIX. 



From the various circumftances already mentioned, in the 

 courfe of this tedious, yet neceffary recital, it had been for a 

 confiderable fpace of time forefeen, that the refult given by 

 the meafurement with the deal rods muil be entirely rejeded, 



generally in excefs, from handling the inftruments. One degree of alteration, 

 producing a difference of about TsV^th part of aa inch in the twenty feet, ^vas 

 very eafily and accurately allowed for by fiich a tnicrometer as this, which fliewed 

 the coincidence of the ivory interfeftion with the diamond line to be more or lefs 

 perfeft, when the head of the fcrew was moved two djvifiQns, that is to fay, 

 i-sf&gths or T^Wth part of an ijich. 



N n n 2 snd 



