STANDARDS OF LINEAR MEASURE. 
381 
With wires .05 of an inch diameter. 
From 0 to 36 inches. 
Without Wires. 
A Wire under 
Wires under 
Error when curved 
Error when curved 
Sum of 
the middle. 
the ends. 
upwards. 
downwards. 
Errors. 
div. 
div. 
div. 
div. 
div. 
div. 
38.5 
35.5 
43.0 
39.5 
32.5 
39.5 
36.2 
31.5 
39.0 
Mean 38.1 
33.2 
40.5 
7.0 
0.3 
7.3 
2.1 Reduction to the Chord. 
40.2 
From these last Tables it appears that the sum of the greatest errors to which 
the Russian scale is liable from flexure is the greatest possible when the versed 
sine is .04 of an inch, and is then equal to nine divisions of the micrometer, or 
.00038 of an inch, which, reduced as in the foregoing experiments with the 
other scales to a versed sine of .01 of an inch, gives for the comparative sum of 
the errors due to such versed sine .00009, or about one ten-thousandth of an 
inch. 
It is evident that the advantage of this construction consists merely in the 
employment of a thin plate to receive the divisions, instead of a bar of greater 
thickness ; but a plate sufficiently thin could not well be used without a firm 
support, which is necessary to protect it from injury, as well as to prevent the 
plate from being affected by any sudden variation of temperature, either from 
partial currents of air, or from the vicinity of the person of the observer. 
