Henry William Chisholm.

On the science of weighing and measuring and standards of measure and weight online

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1303, it being recited in a weights and measures
statute of that year, 31 Edward III. The word
" avoirdepois," as applied to commodities, occurs in
earlier statutes of the gth and 27th of Edward III.
The pound avoirdupois was evidently taken from the
old French commercial pound of sixteen ounces, which
was used in many parts of France. Our existing
avoirdupois pound can be clearly proved to be of
similar weight to the standard avoirdupois pound of
Edward III., and there is good ground for believing
that no substantial difference has occurred in its
weight, or in that of the troy pound, since either of
them was first established as a standard in this
country. There is no evidence of any direct relation
between the two units, the pound troy and the pound
avoirdupois, when first introduced and legalised, pro-



bably at the same period, in this country. But we
know from the Elizabethan standards that the pound
avoirdupois was equal to about 7,000 grains, of which
the troy pound contained 5,760 grains.

41. As regards the actual standards of avoirdupois
weight, official records show that the series of Ex-
chequer standard avoirdupois weights constructed
in the reign of Queen Elizabeth, by which all the


commercial weights of this country were regulated up
to the reign of George IV., and then remaining in the
Exchequer, were derived from a 56-lb. avoirdupois
standard of Edward III. But no trace could be found
of this old standard in 1758, when inquiry was made
for it by the Weights and Measures Committee of
the House of Commons. New standard weights had,
however, been constructed in the twelfth year of
Henry VII., and in the Act, 12 Henry VII., which
legalised them, it is expressly mentioned that the king



"did make weights and measures according to old
standards thereof remaining within his treasury." The
original Exchequer standard weights of Henry VII.
were destroyed when new standards were legalised


by Queen Elizabeth, but some of the copies distri-
buted to the several counties and principal cities
have remained up to the present time. Figure 13
represents the brass 14-lb. avoirdupois standard


weight of the set supplied to the city of Exeter, and
formerly kept in the Guildhall there. It is now
deposited in the Albert Museum in that city.

A' portion of a series of avoirdupois standard
weights, constructed in the seventeenth year of
Queen Elizabeth's reign, was recently found de-
posited in the old Pyx Chamber. This set had, how-

OF 8-oz. AND 4-oz. WEIGHTS (actual size).

ever, been condemned as inaccurate at a later period
of her reign, and it is evident that they had never been
properly adjusted. These weights are of gun-metal,
with iron rings, and are distinguishable from the
later and more accurate set of Queen Elizabeth's
avoirdupois standards by being marked with a rose.
They are of elegant form, as may be seen from fig.
14, representing the H2-lb. weight.

The more accurate and complete set of Exchequer
standard weights, constructed in 1588 under Queen


Elizabeth's orders, and made of bell-metal, are still
in good condition. They were used to regulate all
the weights in the kingdom until 1824, when the
new imperial standard weights, constructed under
Captain Kater's directions, were substituted for them
under 5 Geo. IV. c. 74. The set of troy standards

BELL-SHAPED (actual size).

from I oz. to 256 ozs. are in the form of cup weights
fitting into each other. There is no single weight of
a pound troy, but the Exchequer standard of the
troy pound was formed of the two weights of 8 oz.
and 4 oz. as shown in fig. 15.

There are two sets of avoirdupois standards. The
larger set, from 56 Ibs. to I lb., is bell-shaped, as shown


in fig. 1 6. This avoirdupois pound is believed to have
been originally equal to about 7,002 troy grains. In
1758 the Weights and Measures Committee of the
House of Commons reported it to weigh 7,000^5
troy grains. In 1873 it weighed 6,999 grains of the

FLAT DISC SHAPE (actual size).

imperial standard. It thus appears to have lost only
three grains in weight, though continually used as an
Exchequer standard from 1588 to 1825.

The smaller set of Elizabethan avoirdupois stand-
ards, from 8 Ibs. to I dram in a continued binary


series, consists of flat circular weights, as shown in
fig. 17. This avoirdupois pound was found in 1758 to
weigh 6,997-5 troy grains. In 1873 it was found equal
to 6,996-4 grains of the imperial standard.

The bell shape, with its convenient handle, has


generally been preferred for the larger avoirdupois
standard weights, both for lifting and carrying them
over the shoulder. The form shown above is that which
has been generally adopted for local standard weights.


42. As to our early English standard measures of
capacity, the first of which we have any cognizance are
the Winchester corn-bushel, of a capacity of 2,150^
cubic inches, and the Winchester corn-gallon, of 274^
cubic inches. The oldest standards of these measures
that now remain in the Standards Office are those
constructed by order of Henry VII. CFigs. 19 and 20).


A standard ale gallon of 282 cubic inches was
added by Queen Elizabeth in her new set of standard
measures constructed in 1601, the standard quart of
which is here shown (Fig. 21). In 1707 another addi-
tion was made to the Exchequer standards by Queen
Anne, of a standard wine-gallon of 231 cubic inches
(Fig. 22). But all these standard measures of capacity




were abolished in 1824, when the new imperial
standard gallon, containing 10 Ibs. weight of water


and of the capacity of nearly 272^ cubic inches, was
made the standard of capacity for liquid measures,
and the imperial standard bushel of eight gallons was


made the standard for measuring grain and dry

43. All the before-mentioned old English standards
were brought under the notice of the Weights and
Measures Committee of the House of Commons, who
sat in 1758 and the two following sessions. Many
recommendations were made by this committee in
relation to our standards, which were not, however,



then carried into effect by law. Under their directions
a new standard yard and^tandard troy pound, both
of brass, were constructed, and were intended to. be
constituted the legal standards of length and weight
in this country. Meanwhile they were left in the
custody of the Clerk of the House of Commons.
But it was not until 1824 that the new imperial
system of weights and measures was legalised, in

F 2


the Act 5 Geo. IV. c. 74. In this Act the standard
yard of 1760, and the brass troy pound of 1758,
both in the custody of the Clerk of the House of
Commons, and denominated respectively the " Im-
perial Standard Yard " and the " Imperial Standard
Troy Pound " were declared to be the only " original


and genuine standards," from which all other imperial
weights and measures were to be derived. No pro-
vision was contained in the Act of 1824 for removing
the,vtwo primary standards from the House of
Commons, and the result was that they were de-
stroyed by the burning of the Houses of Parliament
on i6th October, 1834. The lost standard pound


was similar to that represented in Fig. 23, showing
the original standard troy pound of 1758, now in

FIG. 23. STANDARD TROY POUND OF 1758 (actual size).

the Standards Office, from which the lost standard *y /
had been constructed.

IV. Tke Restored Standards. Imperial Standard
Pound and Yard.

44. The legal standard units of imperial weight and
measure are now the standard pound avoirdupois and
the standard yard constructed under the superintend-
ence of the Standards Commission, appointe.d in
1843, for the restoration of the lost standards of
weight 'and measure.


The members of this Standards Commission had
previously given their services as a preliminary com-
mitteee, having been appointed in 1838 to consider
the steps to be taken for restoring the standards ;
the Act of 1824 (5 Geo. IV. c. 74), under the authority
of which the lost standards had been legalised, having
directed that, in the event of their loss or destruction,
new standards should be constructed in accordance
with provisions contained in the Act, by reference to
an invariable natural standard.

These provisions were as follows : In regard to
the Standard of Weight, it was recited in 5 of the
Act, that a cubic inch of distilled water, weighed in
air against brass weights, at the temperature of 62
Fahr., the barometer being at thirty inches, had been
determined by scientific men to be equal to 252-458
grains, of which the standard troy pound contained
5,760 ; and if this standard were lost or destroyed,
a new standard troy pound was to be constructed
bearing the same proportion to the weight of a cubic
inch of water, as the standard pound bore to such
cubic inch of water.

It will thus be seen that the new unit of weight
was to be dependent upon the new unit of length,
it was to be based upon the capacity of the cubic
inch, or the cube of the thirty-sixth part of the
standard yard.

With respect to the standard unit of length, 3
of the Act recited that the imperial standard yard,
when compared with a pendulum vibrating seconds
of mean time in the latitude of London, in a vacuum
at the level of the sea, had also been determined to


be in the proportion of 36 inches to 39*1393 inches,
and it was provided that if lost or destroyed, a new
standard yard should be constructed bearing the
same proportion to such pendulum as the imperial
standard yard then bore to it.

After long deliberation, the committee made a
very full report, dated December 21, 1841, and
declared their opinion that the several elements of
reduction of the pendulum experiments referred to
in the Act of 1824, were doubtful or erroneous.
It was evident, therefore, that the course prescribed
by the Act would not necessarily reproduce the
standard yard. It appeared also that the determi-
nation of the weight of a cubic inch of water was still
doubtful, differences being found between the best
English, French, Austrian, Swedish, and Russian
determinations, amounting to about y^Vrr of the whole
weight, whereas the results of the mere operation of
weighing might be determined within j oooooo f the
whole weight. The committee were fully persuaded
that with reasonable precautions it would always be
possible to provide for the accurate restoration of
standards by means of material copies which had
been compared with them. They had ascertained that
several measures existed which had been most care-
fully compared with the former standard yard, and
several weights, which had been most accurately
compared with the lost standard pound, and they
expressed their opinion that by the use of these the
values of the original standards could be restored
without sensible error.

They recommended that no change should be made


in the values of the primary units of the weights and
measures of the kingdom, or in the meaning of the
names by which they were commonly denoted ; that
the construction of the standards be entrusted to a
committee of scientific men, under certain instructions
contained in the report, and by comparison with the
most carefully selected specimens ; that the parlia-
mentary standard of length be one yard, there
appearing no sufficient reason for departing from the
length hitherto adopted for the standard ; and that
the avoirdupois pound be adopted instead of the troy
pound as the parliamentary standard of weight, the
avoirdupois pound being invariably known and
generally used, and the troy pound being wholly
unknown to the great mass of the British population,
and comparatively useless. They also recommended
that no new specific standard of capacity be es-
tablished, the_ unit of capacity, the gallon, being
continued to be defined by its containing 10 Ibs.
weight of distilled water, as specified in the Act
~ ~

Many other important recommendations were also
made by the committee relating to the official
secondary standards, and to the verification and
legalising of local standards for the use of inspectors
of weights and measures throughout the country and
for the colonies ; as well as to the regulation of the
duties of these local officers, in order to secure due
uniformity in commercial weights and measures, and
their accordance with the scientifically constructed
primary standards.

For more effectually carrying out the recom-


mendations for the construction of the new stand-
ards, the Standards Commission was appointed in
1843, and continued their labours until 1854, when
they presented their definitive report.

The Astronomer-Royal, Mr. Airy (now Sir G. B.
Airy, K.C.B.), was chairman both of the preliminary
committee and of the commission. The other nine
members of the commission were all eminent men
of science. The mode in which the commission per-
formed their duties in the restoration of the standards,
and the results of their labours, as shown in their
definitive report, will next be described.

Construction of Nciv Imperial Standard Pound.

45. The mode of constructing the new standard of
weight, together with full details of all the scientific
processes employed, has been described by Prof.
W. H. Miller, the member of the commission to
whom its construction was mo-re immediately en-
trusted. (See/Yy. Trans. 1856, Part III.)

46. For constructing this standard, the first point to
be determined was the exact weight and density of the
lost standard troy pound, from which the weight of
the new standard avoirdupois pound was to be
derived. Upon investigation this proved to be the
most difficult problem to be solved by the commis-
sion. The old standard had been constructed in
1758, under the direction of the parliamentary com-
mittee of that year, together with three similar troy
pounds. It is stated to have been composed of gun-
metal, but unfortunately no record existed of its


volume or density, and it is not probable that it was
ever weighed in water. An accurate drawing of the
lost standard pound had been made in 1829 by
Captain Nehus, who measured its dimensions with
the greatest care. (See Phil. Trans. 1836, p. 361.)
From a comparison of this drawing and the dimen-
sions with the three other troy pounds, the density
of the lost standard was assumed by Prof. Miller to
be 8-15 r.

The three other troy pounds constructed in 1758
were found by the commission to differ slightly in
their dimensions, as well as in volume and weight.
They were all in good preservation and were carefully
examined by Prof. Miller, but there was no satisfactory
evidence of their having been accurately compared
with the lost standard, so as to identify its weight, and
thus to render them available for determining the
proper weight of the new standard. The troy pound
of 1758, now in the Standards Department, was
computed by Prof. Miller to weigh in air 5759'85625
grains of the lost standard.

For ascertaining the exact weight of the lost
standard pound, the following weights, which had
been accurately compared with it, were also ex-
amined :

The brass troy Exchequer standard pound, constructed in 1824

under the superintendence of Captain Katcr, and legalised as the

secondary official standard ;
Three similar brass pounds, constructed for the cities of London,

Edinburgh, and Dublin ;
A platinum troy pound and two brass troy pounds belonging lo

Prof. Schumacher ;
The platinum troy pound of the Royal Society.


47. 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 oxidation or other causes. It was conse-
quently resolved to rest entirely for evidence of the
weight of the lost standard on the comparisons of the
two platinum troy pounds of Prof. Schumacher and
of the Royal Society, denoted as Sp and RS. These
two platinum 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 U by Captain Nehus at
Somerset House in 1829, with the following results:

Mean of 300 observations, Sp = U o '0085 7 grain (mean - c/-b $
t - 650-62 F. b = 29722 in.) -tj.^^

Mean of 140 observations, RS = U 0*00205 grain (mean
/ = 65073 F. b = 29-806 in.)

The density of Sp had been determined, by weigh-
ing it in water, to be 2 r 1874; and it was found to
displace O'32544 gr. of air of the stated mean
temperature and atmospheric pressure. The density
of U was assumed to be 8'I5I, which is nearly the
average density of brass and bronze weights, and U
therefore displaced o 84646 gr. Whence in a vacuum
Sp = U - 0-52959 gr/ J

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 032629 gr. of air, whilst U displaced o - 84865
gr. Whence in a vacuum RS = U 0*52441 gr.
The mean value of the lost standard troy pound

/T ^


thus determined through Sp and RS, was the basis
upon which the new standard avoirdupois pound
was to be constructed.

48. As a preliminary operation, a new platinum
troy pound, denoted as T, was constructed very
nearly equal to Sp and to RS, and taking the mean


(actual size).

of 286 comparisons of T with Sp, and of 122 com-
parisons of T with RS, it was found that in a

T = Sp + 0-00105, whence T = U 0-52851
T RS 0-00429, whence T r= U 0-52870.

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 determined that in a vacuum

T = U - 0-52857 gr., or = 5759'47i43 g.

It was also found that in air, / = 65 66 F. b 2975
in., which was the mean of the comparisons of Sp and
RS with U, and was adopted by Prof. Miller as the
standard air, T = y _ 0-00745 gr.

The form and size of the two platinum troy pounds
RS and T are shown in Figs. 24 and 25 ; RS being a
truncated pyramid surmounted with a knob, and T a
cylinder with a groove.

It should here 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 construct the new avoir-
dupois standard pound, and to accurately adjust its
weight of 7,000 grains in a vacuum, from the troy
pound T. For this purpose four new platinum weights
of 1,240 gr. each were constructed, all accurately veri-
fied in terms of T, and by employing other platinum
weights, viz. one each, of 800 440, and 360 gr., four of ^
80, and two of 40 gr., the true weight in a vacuum of
each of the i,24Ogr. weights, as separately determined
by numerous comparisons withT and with each other,

as follows : Grains.

A = 1239-88622

B = 1239-88605

C = 1239-88597

D = 1239-88580

Mean = 1239-88601
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 approxi-
mate weight of 0-645 gr. was obtained from T in the
following manner. By comparisons with the two
4 g r - 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 =
6-451 gr. From V was derived Q = 0*64509 gr., the
mean of ten weights of platinum wire, each equal to
0-645 gr. very nearly. It will be shown hereafter, in
describing the mode of weighing with a scientific
balance, that small differences between two standard
pound weights of less than O'l gf. are ascertained by
the index scale of the balance. Means were thus
afforded of determining the exact weight of 7,000 gr.,
which was to be the weight in a vacuum of the
new standard.

49. The new imperial standard pound was con-
structed of platinum, and denoted as PS or Parlia-
mentary Standard. Its form and size have been
already shown in Fig. I.

The true weight of PS was actually determined
from the mean result of 340 comparisons with the
following platinum weights, viz. :

gr. o mm.

PS = T+Q + H A + B + C + D)- 0-00177 in air / - 19-28 C. b = 759 12.

The density of PS was determined by weighing in
water to be 21*1572, and that of T and the smaller
platinum weights to be 2ri66i. PS consequently
displaced 039744 gr. of air, and T + Q + i (A +
B + C + D) 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 deemed to
contain 7,000 grains of the new standard.

50. Four similar platinum pounds were constructed
at the same time, and their weight in terms of the
new standard PS accurately determined. These four
pounds 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 (PC), and
were deposited as follows :

PC, No. i, 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 Westminster.

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.
Miller, was accurately determined, as well as the
densities of all the new standard pounds. These gilt
bronze pounds were distributed amongst different
countries and public institutions 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 of the Construction of tJw
new National Standard of Weight.

51. The new imperial standard pound is of the true
weight of an avoirdupois pound when in a vacuum.


The principal advantage of the metal of which it is
composed (platinum) consists in its not being affected
by oxidation, which would unavoidably alter its ab-
solute weight. But platinum has this disadvantage,*
if used as the material of a standard for regulating
ordinary weights of precision made of brass, viz. that
when weighed in air against a brass or bronze standard
weight of so much greater volume, although of equal
weight in a vacuum, its apparent weight is always
more than half a grain greater than that of the brass
or bronze standard. To obviate this disadvantage, the
weight in air of all the bronze standard pounds
verified by Prof. Miller were computed by him, not in
terms of the platinum standard pound, but of an ideal
brass commercial standard pound, denoted by him as W.
He assumed W to be of the same density as the lost
standard, and of the average density of brass or
bronze. In air, t = 6$-66, b = 2975 in., PS with a
density of 21-1572 displaced 0-39644 gr. of air, and
W was assumed to displace 1-03051 gr. And as

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Online LibraryHenry William ChisholmOn the science of weighing and measuring and standards of measure and weight → online text (page 5 of 12)