338 An Account of the Comparison of 
whether this difference was observed to be in excess or in de- 
fect. 
As it was possible that this standard yard of 1760 might coin- 
cide with 36 inches of Sir George Shuckburgh’s, scale, I was 
anxious to compare them together, and by the exertions of Davies 
Gilbert, Esq., M.P., the standard of 1760. was found in the cus- 
tody of the House of Commons, and confided to my care. It is 
(as Sir George Shuckburgh observed) precisely similar in form to 
the standard of 1755, the yard being marked by two dots upon 
gold pins, which, though very large, are in tolerable preservation. 
‘The five standard scales which I have just described, were 
placed together on the loth of June 1820, and arranged so that 
those of least bulk should be furthest from me during the obser- 
vations, as they would be more readily affected by the proximity 
of the person of the observer. 
As I was desirous that comparisons of such importance should 
not rest wholly on my own authority, 1 requested Dr. Wollaston 
to take two series of measurements, which, together with my 
own, are contained in the following table. 
TaBLeE III. 
Comparisons of various Standards. 
3 Readings of the micrometer at 
5 
Date. ro The Sir Geo. pie Colonel 
3 Royal General Suurks Bird’s wae. 
re baess y's > | Standard : 
1820. & |Society’s| <oole burgh’s £1760. | 02’ 
& |standard. "1 scale. standard 
June 16) 61°5 19 23 43 43 66 
— 6 17 41°5 41°5 58 
er 8 14 36 36 50 
— 86 92 118 118 133 
64:0 75 93 114 114 121 
— 82 91 lll 106 126 
— 78 93 112 108 127 
63°5 75 93 118 110 124 
17; 61°5 15 24 44 40 59 
4 17 39 36 53 
nat 1 14 35 36 45 
» | 64°5 59 70 94 94 115 
(By Dr. Wollaston) 18) 64°5 30 39 64 64 76 
| 21 386 56 56 66 
(By ditto 
Mean of the whole..........000) 401 
I now returned to the forty-inch iron bar and General Roy’s 
scale, anxious to verify my former conclusion by a fresh examina- 
tion. The-microscopes being fixed at the proper distance, com- 
parisons were made, which I shall detail before I state the results 
afforded by the preceding table. 
TABLE 
