404 M^jor-General 'R.oy's Account of the 



cond pin. The beam being then removed, and one point 

 placed in the interfection of the arc and wire, with the other 

 point a dot was made on the third pin, under the middle of 

 the wire. Upon this dot, as a center, a faint arc was next 

 defcribed on the fame pin where tiie firft had been traced. In. 

 this manner the fix times forty inches were marked off, alter- 

 nately with dots and arcs ; a method found by Mr. Ramsden, 

 in' his practice, to be more accurate, than when dots only are 

 made ufe of. 



The exa6l length of twenty feet, thus obtained, was next 

 ' taken between the points of the long beam-compaffes, and 

 transferred to thetops of the bell-metal cocks, pilaced, as has 

 been already mentioned, on the fide of the frandard rod, in 

 fucli m^anner as to leave more than one inch and a half of the 

 faid cocks beyond or without the luies denoting the extent of 

 the twenty feet. This being done, the meafuring rods were 

 fuccefiively placed on the ftandard, and their fides applying 

 clofe to the cocks, the diftance of twenty feet was readily 

 transferred from them to the inlaid ivory pieces, on which fine 

 lines were afterwards cut, by marks accurately made for that 

 purpofe. 



With regard to the adjuflmcnt of the lips of the 'bell-metal" 

 tippings, which extend exadly one inch and a half beyond the 

 ivory lines, fo as to make the total length of the rod 243 

 inches, it is to be obferved, tliat they terminate in flat curves 

 of 3^ inches radius, pafling through the inch and half points, 

 to which they were cautioufly ground down, that at firfl they 

 migl:it rather exceed than be defective in length. Any two 

 of the rods, lying in the fiune plane, and alio in the fame 

 ilraigljt line, being brought into contad with each other ; if 



of 



