44 On the Length of the French Meéire 
might have arisen from the edges of the métre projecting beyond 
its terminating planes. Each of the brass pieces was supported 
in this position upon a piece of lead of a sufficient thickness, and 
kept in close contact with the end of the métre by means of a 
slight spring bearing against a pin driven perpendicularly into 
the lead. . 
In order to ensure a perfect contact between each brass piece 
and the terminating plane of the métre, a flat ruler of brass was 
laid upon the surface of the métre so as to project beyond its ex- 
tremity, and the end of the lead was elevated or depressed so 
that the line of light seen between the piece of brass and the 
ruler, the eye being level with the surface of the brass, apppeared 
to be equal in every part; when it was inferred that the surfaces 
of the métre and of the piece of brass were parallel, and conse- 
quently that their rectangular ends were perfectly in contact. 
The distance hetween the lines on D and d was now taken 
by the microscopes, and transferred to the scale in the manner 
before described ; and when a sufficient nuinber of comparisons 
had thus been made, the pieces D and d were exchanged for 
those marked C and c, and the observations repeated with every 
precaution to ensure an accurate result, ‘especially with respect 
to temperature. : 
The under surface of the métre was then placed uppermost, 
and the apparatus being arranged as before, the same process 
was pursued as that which has just been described. The results 
are contained in the following tables. 
Comparison of the Metre d bouts. 
The pieces D andd applied. Distance trom D to d, 
456-7 divisions. The word Metre above. 
3 as, a2 os, 2 e285 |2,5 0 
a laee.jce8.| 2 latesluce |453 slosefes 
= Oe Gg] Ou Re 2) alms ag 2 aie 2 
ai ef S oe 2 on ee o gs] Oo 8 DU we 
a mhog) WE o S ma ose) = sete Paes 
c si9 49 Ferd, 9S as i GDaES 2p eS S| Se e 
See Soe ee al es SP OS) Mes pe SB A) co ee 
FE /e20 |e6a7| & lS ot7| €T (bes | ges ad 
4 er) ons 2 = 5) 
ita gree) a Ca) coca. ae 
597 | 95 915 | 820 | 538-7 |39°37594] -OO6L0 | 59 57083" 
54-8 380 972 59°92} 515°9 |39-37792 ‘OO0T13 | 39°37079 
550 | 39:0 98-0 59°) | 515°7 (39937793) OOTN9 | S9-37084 
551 | 36*2 95°0 §s°8 | 515°5S  159°37794) 00707 | 39:37087 
Sara. 1) 9") 59-0 5147 139°375795]-00705 | 59-37088 
Mean | 5937084 
The pieces C and c applied. Distance from C to c, 
500°5 divisions. The word Meélre above. 
26) Su7T | 479 168 J olT> [3y3B77To6] UW6YO | BY orlUyU 
55:7 | $00 473 17-3 | 517-8 |39°37784]-00694 | 39°37090 
559 | S02 475 173 | 5178 |39-37784]-00690 | 39-37094 
56-2 | 24-5 45-0 1205 | 521-0 139°37770] 00684 | 59°37086 
565 | 290 | 44-7 4.217 | 5222 |39.97765| 00681 | 39-97084 
Mean | 39°37089 
