STANDARDS OF LINEAR MEASURE. 
377 
the length of the string. So delicate is this test by sound, that a concavity can 
be detected by this method where the interval between the wire and the sur- 
face under examination is not to be perceived by the eye. 
Having now a means superior to any I before possessed of examining a plane 
surface, I applied it to the marble slab, and detected a slight concavity not 
exceeding one-hundredth of an inch. This was corrected by placing cards 
under different parts of the marble. When I had adjusted it so that no irre- 
gularity was perceptible, I thought it necessary to repeat my former compa- 
risons. 
The marble most carefully made plane by the bow. 
Date. 
183-0. 
Imperial 
Standard 
Yard. 
Sir George 
Shuckburgh’s 
Scale. 
Russian 
Scale. 
Mr. Dol- 
lonh’s Scale. 
div. 
div. 
div. 
div. 
May 31 
7 
5.5 
26 
31.0 
4.5 
6.2 
25 
33.0 
4.7 
7.0 
24 
33.2 
4.7 
4.8 
23.2 
32 
3.3 
3.3 
20 
30 
June 1 
4.0 
6.0 
22 
31.2 
7.0 
4.0 
22 
30.0 
5.0 
4.0 
21 
32 
2 
10 
6.0 
23.5 
31.3 
8 
3.0 
25 
31 
6.3 
3.0 
22 
32.5 
6 
4.5 
21.2 
30 
3 
3.5 
23.5 
31 
7 
4 
21.5 
30.5 
3 
98.0 
97 
114.5 
122.3 
97-5 
96.5 
115 
123.5 
4 
28 
22 
43 
53 
27.5 
20 
40.5 
51 
5 
38.0 
33.5 
53 
59.5 
37-3 
31 
50 
59.3 
Mean .... 
20.34 
18.24 
36.79 
45.36 
Read? s oflmp 1 . Stand.Y d 
20.34 
20.34 
20.34 
Diff. from Imp 1 Stand. Y d 
2.10 
16.45 
25.02 
From these differences converted into inches, we have now the following di- 
stances from 0 to 36 inches on each scale in parts of the Imperial standard yard. 
Sir George Shuckburgh’s scale . . . 36.00009 inches. 
The Russian scale 35.99929 
Mr. Dollond’s scale 35.99893 
3 c 2 
