STANDARDS OF LINEAR MEASURE. 
363 
as the microscopes invert, an increase in the readings of the micrometer indi- 
cates that the scale is shorter than that with which it is compared, and vice 
versa. The value of one division of the micrometer is .0000428742 of an inch. 
Date. 
1830. 
Therm. 
Imperial 
Standard 
Yard. 
Sir George 
Shuckburgh’s 
Scale. 
Russian 
Scale. 
Mr. 
Doleond’s 
Scale. 
Captain 
Eater’s 
Scale. 
div. 
div. 
div. 
div. 
div. 
May 1 
66 
7 
0.5 
23 
27-5 
32.7 
8.2 
2.0 
23.7 
25 
30 
2 
63 
104 
98 
120 
124.5 
126 
76.5 
72.5 
95 
101 
101 
8.7 
5 
22.5 
28.5 
37 
66 
88 
80.5 
95 
104 
110.5 
3 
62 
3.5 
2 
23 
27 
28.2 
3 
0 
24.5 
26 
.... 
102.5 
96 
117 
125 
131 
17 
14 
35.5 
42 
46 
64 
10.7 
4 
22.5 
28.3 
37 
4 
61 
20.2 
16 
39 
40 
51 
20 
16.5 
37 
43.6 
47.5 
62 
18 
16 
34.6 
42 
46 
5 
63 
15 
10.7 
28 
37 
37.7 
14 
10 
26.7 
33.5 
42 
Means. . . 32.02 
Readings of Imperial Stand. Yd. 
27-73 
32.02 
47.94 
32.02 
53.43 
32.02 
60.24 
32.02 
Differ, from Imperial Stand. Yd. 
4.29 
15.92 
21.41 
28.22 
Converting these differences of the readings of the micrometer into inches, 
we obtain the distances from zero to thirty-six inches on each scale in parts of 
the Imperial standard yard. 
Sir George Shuckburgh’s scale . . . 36.00018 inches 
The Russian scale 35.99932 
Mr. Dollond’s scale 35.99908 
Captain Rater’s scale 35.99879 
Here it is seen that Mr. Dollond’s scale, which by careful comparisons in 
the years 1820 and 1824 appeared to differ little, if at all, from Sir George 
Shuckburgh’s scale, is now no less than .0011 of an inch in defect. 
I now resolved to determine the amount of the error which might arise 
from the flexure of a bar of known thickness, the curvature of the surface upon 
which it is placed being given. 
