ON THE COMPARISON OF LINE AND END STANDARDS. 249 
Six determinations of the value of the space were made in 
all, each determination consisting of six measurements with 
each of the two micrometers belonging to the Comparator. 
Between them the surfaces were separated, readjusted, and 
mounted on the tripod under the microscope. 
The mean of the six determinations gave 1627^.82 as the 
db.16 
distance between the lines. 
Three independent comparisons, by as many observers, of 
the combined length of the Committee metre and abutting 
pieces were made with No. 21, between which the abutting 
pieces were readjusted and exchanged. 
It is unnecessary to describe in detail the adjustment of 
the abutting pieces on the ends of the Committee metre; 
methods for doing this would naturally suggest themselves 
to any one attempting to use the method. It is, however, 
important to keep in mind that the end surfaces of the Com¬ 
mittee metre are perpendicular to the axis of the bar, and 
hence, when the pieces were in contact, the contact surfaces 
were parallel and separated by the length of the metre. 
The result of the comparisons with No. 21 gave the fol¬ 
lowing value for the combined length at 0°.0 centigrade: 
0. M. + abutting pieces = l m + 1625 |U '.97 
±.08. 
Subtracting from this the value of the abutting pieces found 
above, we get— 
C. M. = l m —ff.35 
±.18, 
a result that is smaller than either of the former ones re¬ 
ferred to. 
The condition of the end surfaces is doubtless responsible 
to a great extent for the disagreement of the results by the 
different methods, but it is difficult to account for the small 
value due to the last method. One would naturally expect 
it to give the larger value, since the value determined in 
this way is the length between the higher points of the sur¬ 
faces. 
36—Bull. Phil, Soc., WajSh./iVol, 13 
