g58 SURVEY OF THE COAST 



like the bars themselves, and rubbed with emerv and oil, to 

 serve as butt ends, for the final adjustment of the i)ars. 



To execute tliis, (he iron plate of the filing tool was fitted 

 tight in the end of a |)lank, so as to continue its plane over 

 the whole of it, to a greater length than the bars, and the 

 plank was then planed, so as to form an exact continuation 

 of the plane of the iron plate. Upon this plane tlie four 

 bars were laid along side of each other, pressed together be- 

 tween brass |)ins and wooden wedges, and held down by 

 wooden clan)ps. The ends upon the plank were butted by 

 a straight piece of wood. '1 he ends on the iron plate were 

 rubbed with the seven inch long buttutg piece, with emery 

 and oil ; changing their relative position occasionally, until 

 their ends piesented, in all positions, one even, i)lane, and 

 smootl) surface, upon which the rubbing piece touched 

 equally in all places, so as to |)resent with them all one even, 

 sharp, and straight line at their upper surface. 



They were tlien all turned end for end, and made to fit 

 against the five incli iron butting piece, so as to present again 

 one even and sharp line, to whicli they were of course per- 

 pendicular. In this position, they were again fastened as 

 before, and rubbed again with the seven inch butting piece, 

 changing their relative position, until they presented, at these 

 ends also, one uniform regular surface and sharp top line. 

 The two iron meties of the Committee and Lenoir were 

 then laid upon them, and appeared to coincide with them in 

 length. 'Ibis was of course tried several times ; wishing 

 however to suffer them to be somewhat longer, because tl)e 

 cooling down of the metal, which is always more or less 

 heated l>y the working, will always short'u them somewhat. 

 Indi-ed I have observed that the copies of measures made in 

 this way are generally shorter than their oiiginals, from this 

 circumstance ; their compar'son !)eing probably made too 

 soon after the work, and before the metal is actually cooled 

 down to the temperature of the original with which they are 

 compared. 



