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pound, the following weights, which had been accurately 
compared with it, were examined :— 
The brass Troy Exchequer Standard pound, con- 
structed in 1824 under the superintendence of Capt. 
Kater, and legalised as the official Standard ; 
Three similar brass pounds, constructed for the Cities 
of London, Edinburgh, and Dublin ; 
A platinum Troy pound and two brass pounds belong- 
ing to Prof. Schumacher ; 
The platinum Troy pound of the Royal Society. 
It was found, however, from examining the results of 
several weighings of the brass Troy pounds that great 
discrepancies existed, attributable to the effect of oxida- 
tion or other causes. It was consequently resolved to 
rest entirely for evidence of the weight of the lost standard 
on the comparisons of the two platinum Troy pounds ; 
denoted by Prof. Miller as Sp and RS. These two plati- 
num weights had been constructed in 1829, and were 
intended to be equal to the lost Standard (denoted as U) 
when weighed in air. Each of them had been compared 
with V by Capt. Nehus at Somerset House in 1829, with 
the following results :— 
Mean of 300 observations, Sp = U — 0'00857 grain, 
(mean ¢ = 65°62 F. 6 = 29'722 in.) 
Mean of 140 observations, RS = U — o'00205 grains, 
(mean ¢ = 65°73 F. 6 = 29 806 in.) 
The density of Sp had been determined by weighing it 
in water, to be 21°1874, and it was found to displace 
0°32544 gr. of air of the stated mean temperature and 
atmospheric pressure. The density of U had never been 
determined, but it was assumed to be of the same density 
as one of the Troy pounds constructed at the same time, 
viz. 8151, which is nearly the average density of brass 
and bronze weights, and to have therefore displaced 
084646 gr. Whence in avacuum Sp = U — o'52959 gr. 
The density of RS also had not been determined by 
weighing in water, but it was assumed to be of the same 
density as Sp, and therefore to have displaced 0'32629 
gr. of air, whilst U displaced 084865 gr. Whence ina 
vacuum RS = U — o'52441 gr. The mean value of the 
lost Standard Troy pound thus determined through Sp 
and RS, was the basis upon which the new Standard 
Avoirdupois pound was to be constructed. As a_preli- 
minary operation, a new platinum Troy pound, denoted 
as T, was constructed very nearly equal in weight to Sp and 
to RS, and taking the mean of 286 comparisons of T with 
Sp, and of 122 comparisons of T with RS, it was found 
that in a vacuum 
T = Sp + o’oo1os5, whence T = U — 0'52851 
T = RS — 000429, whence T = U - 052870 
From the mean of these two results, giving to the 
first twice the weight of the second, in consequence of Sp 
having been compared about twice as many times with 
U and with T as RS was compared, it was finally deter- 
mined that in a vacuum 
T = U — 052857 gr., or = 5759°47143 grs. 
It was aiso found that in air ¢ = 65°66 F. 6 = 29°753° 
which was the mean of the comparisons of Sp and RS 
with U, and was adopted by Prof. Miller as the standard 
air, 
T = U — 000745 gr. 
It should be observed that all the standard Troy 
pounds were intended to be of their true weight in ordinary 
air, whilst the new standard imperial avoirdupois pound 
was to be made of its true weight when weighed in, or 
reduced to, a vacuum. 
The next process was to determine the weight of the 
new avoirdupois standard pound, of 7,000 grains from 
the Troy pound T of 5,760gr., and for this purpose four 
new platinum weights of 1,240 gr. each were constructed, 
all accurately verified in terms of T, and by employing 
other platinum weights of 800, 500, 400, 80, and 40 gr, 
NATURE 
the true weight in a vacuum of each of the 1,240 gr. 
weights was separately determined by numerous compari- 
sons with T and with each other as follows :— 
Grains. 
123988622 
1239-88605 
1239°88597 
1239°88580 
1239°88601 
Mean 
T + Mean = 6699°35744 
It thus required only a weight of 0°64266 gr. to make 
up the full weight of 7,000 gr. The approximate weight 
0°645 gr. was obtained from T in the following manner, 
By comparisons with the 4o gr. platinum weights, two 
platinum weights of nominally 20 gr. each, were found 
to weigh 19'998 gr. each, from which were derived 
W = 12’901 gr., V = 60451 gr. From V was derived Q 
the mean of ten weights of platinum wire, and equal to 
0645 gr. very nearly, It will be shown, hereafter, in 
describing the mode of weighing witha scientific balance, 
that small differences between two Standard pound 
weights of less than o'l grain are ascertained by the 
index scale of the balance. Means were thus afforded 
of determining the exact weight of 7,000 gr., which was 
the weight in a vacuum of the new standard pound, con- 
structed of platinum, and denoted as PS, or Parlia- 
mentary Standard. 
The weight of PS was actually determined by the 
mean results of 80 comparisons with each of the following 
sets of weights :— 
Now Wl tl 
ek@lesi- 
: gn 4 mm. 
PS=T + Q + A — 0002936 in air 4 = 19°47 C. d. = 758°38 
PS#T+Q+4+B —o'001731 ,, 19°19 759°31 
PS2T+Q+C-—ooor621 ,, 18°83 75438 
PST +Q+D—0°000774 ,, 19 63 74°43 
Mean of all, 
PS=T+Q+}A+B+C+D)— ae in air ¢ = 19°28 C. 3. = 759'12 
The density of PS was determined by weighing in 
water to be 21°1572, and that of T and the smaller plati- 
num weights to be 211661. PS consequently displaced 
0°397 gr. of air, and T+Q-+A displaced 0°39727 gr. 
Hence 
PS = 7000'00093 grains of which U contained 5760, 
Having arrived at this very close approximation to the 
desired weight of the new standard, it was resolved by 
the Commission that PS should be constituted the new 
Imperial Standard pound, and be consequently deemed 
to contain 7000’00000 grains of the new standard. 
Four similar platinum pounds were also constructed, 
and their weight in terms of the new standard PS accu- 
rately determined. These were intended as auxiliary 
Standards of Reference, with the view that either of them 
might replace PS, in case of its destruction or damage. 
They were termed Parliamentary Copies (P.C.), and were 
deposited as follows :— 
PC, No. 1, at the Royal Mint. - 
PC, No. 2, with the Royal Society. 
PC, No. 3, in the Royal Observatory at Greenwich, 
PC, No. 4, immured in the New Palace at West- 
minster. 
Thirty-six other standard pounds of bronze gilt were 
also constructed, and their standard weight, both in a 
vacuum and in the standard air, adopted by Prof. Miiler, 
was accurately determined, as well as the densities of all 
the new standard pounds. These gilt bronze pounds were 
distributed amonyst different countries and public institu- 
tions of this country. 
All the numerous weighings, both in air and in water, of 
the new standard pounds for determining their weights and 
densities were made by Prof. Miller himself, and full details 
of all these operations are given by him in his “ Account 
