OF THE UNITED STATES. S57 



qiicnce of the great surface tliey presented when joined to- 

 jrether, I proceeded soniewliat diircrcnlly for the last 

 finisliing. 



Tlie bars were guaged, as nearly a3 the workman in Lon- 

 don could do it, to the hreadth and tliickness of the metres 

 of tl'.e Committee, and made seven feet four inches long. 

 The doul)ie metre being only al)out six feet seven inches, 

 there were nine inches to be cut off, whicli allowed me to 

 make choice of the best paits of the bars for the cuts, and 

 to avoid the parts near the ends, which are never equally 

 well guaged, because the tools, wliich they are worked with, 

 lose there tluir steady support, and fall off. The pieces 

 so cut off were besides wanted for making the butting pieces 

 for these bars and the metres in the comparisons, and for 

 the final adjustment of these bars, as will be shown here- 

 after. The bars were lettered A, B, C, D, for tlie conve- 

 nience of registering them. After their first cutting, there 

 was enough left in length for the perpendicular tiling. To 

 bring tlicm as nearly as possible to an equal breadth and 

 thickness throughout, so as to present for the final adjustment 

 one entire connected mass, they were all four laid close to 

 each other upon a strong work bench, and pressed together 

 by wcilgcs. In tliis position, they presented, by tlie sum of 

 their breaddis, a surface four inches and a half broad, and 

 by that of tiieir thicknesses, one inch and a half. They were 

 then filed togetlier, with one of the circular three inch files 

 of the above tool, varying their situation successively on 

 both sides and in all positions. By this process they were 

 brought to present, in all the combinations, an equal iireadth 

 and thickness tliroughout. and to lie together like one mass. 



Having thus fitted the bars for lying accurately against the 

 filing tool, they were filed down nearly to their proper length. 

 A projjer arrangement was made to extend the horizontal 

 plane of tlie iron plate, so as to support the whole of the 

 bar. Two of the pieces cut from the ends, one five, the 

 other seven inches long, were adjusted, by the filing tool. 



