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The
Importance Of Etienne Lenoir’s Platinum Measuring Instruments
By William A. Smeaton, Ely, Cambridgeshire, United Kingdom
On 22nd July 1799 the definitive standards of the metric system, the
platinum meter and the platinum kilogram, were ceremonially deposited in the
French National Archives (1), and on 10th December 1799 a law was passed
confirming their status as the only legal standards for measuring length and
mass in France (2). The accurate determination of these standards had
occupied a number of outstanding French scientists for ten years, using
elaborate equipment partly made from platinum by Étienne
Lenoir, a skilled instrument maker. This work had been undertaken after more
than a century of discussion. The events surrounding this momentous occasion
which now affects all our everyday lives are described here.
Before the Revolution in 1789, France, like most European countries, used weights and
measures derived from those of the Romans. The standard weight was the pound
of 16 (sometimes 12) ounces which in France was divided further into 8 gros,
each of 72 grains. The unit of length was the foot of 12 inches, each divided
into 12 lines, though for many purposes a longer unit was preferred — such as
the French toise of 6 feet or the British yard of 3
feet. However units with the same name varied in size from country to country
for example, the French pound and foot were each larger than their British
equivalents. In Britain most standards had been fixed nationally since the
sixteenth century, but in France there were many local variations. This situation
caused difficulties for internal and international commerce, made worse by
the need to calculate in twelfths, sixteenths or other fractions when
converting from one system to another.
When the metric system was first introduced
all units were divided decimally, making calculation easier. However, this
had become possible only in the late Middle Ages, after ‘Arabic’ numerals,
probably of Indian origin, began to replace Roman numbers. Arabic numerals
became common about 1500, but it was not until 1585 that Simon Stevin, a Flemish mathematician showed in his book,
"De Thiende", how fractions could be
expressed in Arabic numerals using a decimal point. His book was soon
translated into French, with an English translation, "Disme: The Art of Tenths", appearing in 1608. As
well as explaining decimal arithmetic, Stevin
advocated the decimal division of weights, measures and currency (3).
Other mathematicians adopted the decimal
fractions. In 1656 in England, Robert Wood, of Oxford, proposed to Oliver
Cromwell, the Lord Protector of the Commonwealth after the execution of King
Charles I, that the pound sterling should be divided into ‘tenths, hunds and thous’, but no action
was taken and Britain, like other countries, retained a currency with awkward
divisions, complicating international trade (4). Wood’s interest, however,
was solely with currency.
A Decimal System of Measures
The Seconds Pendulum:
A Standard Length
An early proposal for a decimal system of
measures came in 1670 from a Frenchman, Gabriel Mouton (1618—1694), a parish
priest in Lyons with a good knowledge of astronomy and
mathematics. He deplored the variety of units of length and proposed a
natural unit based on the size of the Earth. This was the length of a minute
(a sixtieth of a degree) of longitude, to be called the ‘mille’ and divided
into tenths, hundredths and so on. One thousandth of a mille was called the
‘geometric foot’ and Mouton suggested that a pendulum of this length set up
in Lyon, which would oscillate 3,959.2 times in 30 minutes, would be a
convenient and easily verified standard of length.
Mouton’s
work was known of in Paris, where Jean
Picard (1620—1682), an astronomer at the
Observatory, proposed that the length of a pendulum beating seconds in Paris should he
the standard (the seconds pendulum). One third of this, to be called the
‘universal foot’, would differ only slightly from the existing Paris foot. However, Picard did not
advocate its decimal division. By now it was suspected that the Earth was not
a perfect sphere and that the length of both a degree of longitude and the
seconds pendulum (which depends on its distance from the center of the Earth)
might vary from place to place (5). This later became an obstacle to international
acceptance of the metric units determined in France.
Varying Standards of
Mass
During the eighteenth century the lack of
an international system of weights and measures affected the development of
science as well as commerce. In 1783, for example, James Watt, an amateur
chemist as well as an engineer, complained to the chemist Richard Kirwan that he found it difficult to compare some of Kirwan’s quantitative results with those of Antoine
Laurent Lavoisier (1743—1794), the French chemist,
because both had used units with different values. Watt proposed that all
chemists should adopt the same pound, preferably that of Paris which was the most widely used in Europe, and that it should be divided decimally (6). In
1789 Lavoisier published his book, Traité élémentaire de
chimie, which marked the origin of modern
chemistry. Quantitative data are present in abundance and in its English
edition, Elements of Chemistry (1790), the translator, Robert Kerr,
added an appendix with rules for the conversion of French units to British,
see Figure1. It is noteworthy that Lavoisier
expressed some weights as decimal fractions of a pound, as well as the ounces
and grains that he had measured in the laboratory.
Commission of Weights
and Measures
In France, public discontent with many aspects of life in an
absolute monarchy forced King Louis XVI and his government to call elections
to the States-General, the only elected parliamentary body, for the first
time in 175 years. It met in May 1789 with the new name of National Assembly
and assumed the powers of government. Although the Assembly received many
complaints about the lack of uniform weights and measures, it was unable to
act immediately. In June 1789 the Paris Academy of Sciences independently
appointed several members to a Commission of Weights and Measures, with the
task of producing a national system. However, as no progress had been made by
May 1790, the Assembly formally asked the Academy to act and provided the
necessary funds. One member of the Assembly with a special interest in the
project was Charles Maurice Talleyrand (1754—1838). He was not a scientist
but was almost certainly advised by members of the Academy. He favored a
system based on the length of the seconds pendulum,
with the unit of weight defined as the weight of water filling a cube of side
equal to a specified fraction of that length. He did not, however, recommend
the decimal division of the new units. Talleyrand hoped that the system would
be adopted by other countries and proposed that the pendulum should be
measured at a place that would be internationally acceptable: sea level
half-way between the North Pole and the Equator. This was the 45th parallel,
which conveniently crossed the French coast near Bordeaux.
Discussion in Other
Countries
The reform of weights and measures was
also discussed in the British Parliament, and in July 1789 Sir John Riggs
Miller (c.1730-1798) advocated a system based on the length of the seconds
pendulum at the latitude of London. When he raised the
subject again early in 1790 Talleyrand wrote to him, proposing that Britain and France might collaborate, but Miller’s plan was not put
to the vote before the dissolution of Parliament on 10 June 1790. Miller lost his seat at the ensuing election and
the matter was not raised again in Parliament. At Talleyrand’s
suggestion the National Assembly made a direct approach to the British
government, but on 1 December 1790 the Foreign Secretary informed the French
Ambassador in London that the proposed collaboration was not practicable
(7).
In 1785 the United States of America, soon after becoming independent from Britain, adopted a decimal currency, and by 1790 Congress
was considering a decimal system of measures based on the pendulum. This was
proposed by the Secretary of State, Thomas Jefferson, who had an interest in
science, but after much discussion it was decided to retain the British
weights and measures (8). Spain was the only country at this time to show an
interest in the French proposals.
The Meridian as a Preferred Standard
Back
in France, in
September 1790, the Academy of Sciences instructed
several members to determine the length of the seconds
pendulum and the measures derived from it, but before work was started there
was a dramatic volte-face. On 16 February 1791, acting on a proposal by Jean
Charles Borda (1733—1799), the Academy appointed a
new five-member committee to re-examine the proposed fundamental unit of
length and on 19 March they reported that they favored a unit equal to a
ten-millionth of the Earth’s quadrant, the part of the meridian from the
North Pole to the Equator, measured at sea level, and this unit and the units
of weight and volume derived from it were to be divided decimally. No
explanation was given for the rejection of the pendulum, which had been the
preferred unit for more than a century. The academicians pointed out that the
Paris meridian passed almost exactly through Dunkirk, on the north coast of
France, and only a short distance from the Spanish city of Barcelona, both at
sea level, which differed in latitude by 9 degrees and 40 minutes, just over
a tenth of the quadrant. The latitudes could be determined by astronomers
with the best available instruments and the linear distance by the well
established method of triangulation, starting from a carefully measured base
line. The total length of the quadrant could then be calculated and the
fundamental unit derived from it.
Much
of the meridian had been measured in the 1740s, when a large-scale map of France was being
prepared, and since then surveying instruments had been improved. Borda, an engineer with a distinguished naval career as a
navigator, had recently perfected his repeating circle, which in skilled
hands enabled celestial or terrestrial angles to be determined to within a
tenth of a second of circular measure. There have been suggestions that
the desire of the Academy to demonstrate its effectiveness may have been
partly responsible for the abandonment of the pendulum as a standard (9).
However, as well as measuring the meridian, the Academy decided to determine
very accurately the length of the seconds pendulum at Paris, and the task was
undertaken by Borda and Jean Dominique Cassini (1748.-1840), director of the Paris Observatory.
They completed it in the summer of 1792, before the meridian survey was
started. The archives of the Academy are sparse for this period, so nothing
is known about any discussions that went on behind the scenes, but it is
possible that the measurement of the meridian was intended to draw attention
to the importance of the Academy at a time when, like many institutions of
the old regime, it was under attack from extreme revolutionaries (10).
Construction of the
Apparatus
The apparatus used by Borda
and Cassini was constructed by Étienne
Lenoir (1744-1825), an instrument maker, born in Mers,
a village near Blois in the Loire valley.
After being apprenticed to a locksmith he worked in that trade until 1772. He
then found employment with a mathematical instrument maker in Paris and studied mathematics by attending one of the
free courses available to craftsmen. He set up his own business, supplying
specialized astronomical instruments of high quality to leading scientists as
well as making mathematical instruments for a larger market, and around 1784
he collaborated with Borda in perfecting the
repeating circle (11). His close association with Borda
made him an obvious choice to construct the pendulum apparatus at the
Observatory, Figure 2. This consisted of a platinum sphere about 1.5 inches
in diameter of mass 9911 grains (526.1 g) which was suspended by a fine iron
wire about 12 feet long. This oscillated with a half-period of about 2
seconds. As air resistance affected the period, platinum was chosen because
it was the metal with the highest specific gravity and thus occupied the
smallest volume for a given mass. In order to eliminate errors arising from
irregularities in the shape of the sphere, which would alter its center of
gravity, it was, with the aid of a little grease, fitted into an inverted
hemispherical copper cup at the end of the wire so that readings could be
taken with the sphere in several positions and a mean result calculated.
The wire was suspended in front of the
pendulum of a clock beating seconds, and the period of oscillation was determined
by an observer who noted the number of seconds between the times when
the wire and pendulum coincided, and divided this interval by the number of
oscillations. The apparatus was enclosed in an airtight case which had a
glass pane through which observations were made with a telescope and, as the
aim was to determine the length of the seconds
pendulum in a vacuum, allowance was made for variations in air temperature
and pressure. There were other minor but significant corrections (12).
The total length of the wire and sphere
was measured by means of a platinum scale about 12 feet long constructed by
Lenoir. Like the sphere it was made of malleable platinum supplied by Marc Étienne Janety (1739-1820), who
had recently perfected his process for its large-scale production (13). The
scale, 6 lines wide and 1 line thick, was covered by a slightly shorter
copper scale to which it was firmly attached by screws at one end. The metals
had different coefficients of thermal expansion, so after calibration the
device served as a metallic thermometer as well as a measuring instrument,
see Figure 2. The platinum scale was finely ruled by Lenoir. At one end a
graduated platinum tongue, sliding in a groove, made it possible to vary the
total length, and a vernier scale enabled
measurements to be made to within 1/116 line. Corrections were made not only
for thermal expansion of the scale but also for its elongation under its own
weight. After 20 sets of observations the length and period of oscillation of
the wire and sphere were established, and from these figures the length of
the seconds pendulum was calculated as 440.5593
lines (99.49 cm) (14). It is interesting to note that at this time the
importance of the number of significant figures was not understood.
Borda and Cassini performed
these experiments between 15 June and 4 August 1792, but before work could begin on the meridian
survey new instruments had to be made, and there was much work for Lenoir and
his assistants, who probably numbered fewer than ten. Fifteen months were
required for the construction of the four repeating circles needed by the two
teams of surveyors. As Lenoir had experience of making parabolic mirrors for
lighthouses he was asked to provide several powerful lamps to enable the
surveyors to signal to each other at night or in fog. More importantly, he
made four platinum and copper measuring rods similar in size and design to
the rule used in the pendulum experiments.
Since the surveyors would have to work in
all weathers the thermal expansion of the rods was significant. Borda therefore collaborated with Lavoisier,
Treasurer of the Academy and a leading member of the Commission of Weights
and Measures, in determining with great accuracy the coefficients of
expansion of platinum and copper. At Lavoisier’s
house they measured very small changes in length by means of an accurate
comparator, designed and made by Lenoir, who took part in the work. The work
was done between 24 May and 5 June 1793 (15, 16). Being very thin and narrow (see above),
the 12-feet long platinum rods had to be handled with great care. Each rested
in a shallow groove cut in a wooden plank, and in use was covered by a wooden
roof and cloth curtains to protect it from sunlight and minimize expansion
and contraction. The planks bearing the rods were each mounted on two
tripods, with elaborate precautions to ensure that they remained horizontal.
Dunkirk to Barcelona
The survey from Dunkirk to Barcelona required the accurate measurement of more than a
hundred triangles from two base lines, near Melun,
south of Paris, for the northern part and Perpignan for the southern, see Figure 3. The teams of surveyors, led by Jean Baptiste
Joseph Delambre (1749-1820) in the north and by
Pierre François André Méchain (1744-1804) in the
south, took seven weeks to measure the base lines, each approximately 36,000
feet long and requiring about 3,000 movements of the platinum rods. At each
movement two rods had to be precisely aligned, put in exact contact by
adjustment of the sliding tongue on one of them, and then measured. Wherever
possible the corners of the triangles were high points such as hilltops or
church towers, and all the measured distances had to be corrected to allow
for variations in height and the curvature of’ the Earth.
Not surprisingly, the field work and
ensuing calculations required far more time than was anticipated, and the
surveyors were also handicapped by the fact that after the execution of Louis
XVI in January 1793 the French Republic was at war with most of Europe. With their
unfamiliar instruments they were sometimes thought to be spies and were
harassed by the local population.
In 1794, even though the work was far from
complete, the National Convention, the republican successor to the Assembly,
wanted to introduce the new weights and measures and the decimal system as
soon as possible. Therefore a provisional value for the ten-millionth of the
Earth’s quadrant was calculated from the results of the survey done in the
1740s and from the best available figures for the latitudes of Dunkirk and Barcelona. This unit, equal to 3 feet 11.44 lines, was named
the ‘meter’, from the Greek ‘metron’ (measure).
After some discussion the Greek prefixes, ‘deca’,
‘kilo’ and so on were adopted for multiples of the
meter and Latin prefixes such as ‘deci’ and ‘milli’ for sub-multiples. These had been proposed by
Claude Antoine Prieur (1763-1832), a former
engineering officer who was an early advocate of decimal units and was now a
member of the Convention (18). Some time was needed for agreement to be
reached about names for the other units, but eventually the cubic decimeter
became the ‘liter’ and the weight of a cubic centimeter of water at its
temperature of maximum density was named the ‘gram’ [named in French mètre, litre, gramme, respectively].
To be continued
[End of the January
part. the following to be in the February issue, but refs 1-18 and "The
Author" were added to the January material]
The New System of
Measurements
Lenoir made a provisional standard meter
in brass and designed a machine for the manufacture of 660 accurate copies
for distribution to all parts of France. In 1794 the government published a book
explaining the new system and giving conversion tables for the old and new
units (19). This was reprinted in several provincial towns, in some of which
conversion tables for local units were also published. It was decreed that
the use of the metric units should be compulsory from August 1794, but this
was not in fact achieved until many years later.
Decimal currency, introduced as part of
the metric system, was accepted more rapidly, as it was based on the ‘franc’,
a coin containing five grams of silver which was almost equal in
value to the ‘livre’ of the old regime. Circular
measurement was also included in the new system, the right angle being
divided into 100 and the circle into 400 ‘grades’, with decimal
sub-divisions. Lenoir engraved this scale on three of the surveyors’
repeating circles.
The division of the day into 10 hours
instead of 24 received hardly any support and was soon abandoned, but the
Republican calendar, with a year of 12 months, each month being made up of
three ‘decades’ of 10 days with 5 additional days at the end (6 in leap
years), remained in use until 1805.
Preparation of the definitive standards
was delayed not only by wartime problems affecting the surveyors but also by
political developments in Paris.
In July 1793 the Academy of Sciences was suppressed, along with all other organizations
that had received funds from the royal government. The eleven scientists
working on the new units were allowed to continue, but they suffered a severe
blow in November 1793 when Lavoisier, who had been
determining the density of water in experiments conducted with the physicist
René Just Haüy (1743-1822), was arrested together
with all his former colleagues in the Tax Farm, the unpopular private
corporation that collected certain taxes under the old regime. By government
decree Lavoisier was removed from the Commission of
Weights and Measures, as were Borda, Delambre and two other members with links to the old if
regime (20). On 8 May 1794 Lavoisier and nearly
thirty other Tax Farmers were guillotined. He was one of about ten
academicians who suffered violent deaths during the Revolution (21).
When the Commission eventually completed
its work in 1798 the length of the meter was found to be 3 feet 11.296 lines,
slightly shorter than the provisional value of 3 feet 11.44 lines. The
observations and calculations of the Commission were checked by a group of
foreign scientists who spent several months in Paris at the invitation of the French government, as it
was hoped that the new system would be universally adopted. However, Europe was still at war, so only France’s allies at the time and neutral countries were
represented. These were: Spain, Denmark, the Netherlands, Switzerland and several Italian states. The absentees included
Great
Britain, Russia, Sweden, all the German states and the United States of America. Even so, the meeting has some claim to be
regarded as the first international scientific conference (22). Lenoir made
the definitive meter in platinum, and the platinum kilogram (a more useful
standard than the gram) was made by Nicolas Fortin, another famous instrument
maker. It is pleasing to note that they both took part in the ceremony when
the standards were deposited in the National Archives — public recognition of
the importance of skilled craftsmen in the progress of science.
Slow Adoption of the
Metric System
The foreign representatives took accurate
iron copies of the standards to their own countries, but there was little
enthusiasm for the metric system and its international adoption proceeded
very slowly in the nineteenth and twentieth centuries. In 1791 Charles Blagden, the secretary of the Royal Society, had told Sir
Joseph Banks, the then president, that in his opinion the French academicians
wished ‘to divert the attention of the European public from the true amount
of their proposal, which in fact is that their measurement of 9 or 10 degrees
of a meridian in France shall be adopted as the universal standard’ (23). It
is possible that Blagden’s sentiment was shared by
other scientists outside France.
The National institute, the successor to
the Academy of Sciences, decided to permit only metric measurements in its scientific
publications, but even in France there was resistance to the metric system in
commerce, and the old units were still widely used. In 1812 the Napoleonic
government legalized a compromise system with units such as the ‘common foot’
and the ‘common pound’, equal to a third of a meter and half a kilogram,
respectively. This gave rise to confusion with the old feet and pounds, and
for a time the metric system was almost abandoned. It was not until 1840 that
its use became compulsory — fifty years after the reform was initiated (25).
Lenoir’s platinum meter, made in 1799,
remained in use until replaced in 1878 by an international standard made of
iridium-platinum supplied by George Matthey of London (24). The four measuring rods, which had made the
accurate determination of the meter possible, were returned from the
Observatory to Lenoir’s workshop after being inspected by the international
commission, but in 1803 they were again taken to the Observatory.
It was decided that the first platinum
meter, "No,1", which had been measured by Borda,
should remain in the Observatory, but the others were used in 1823 for the
triangulation of Switzerland and Alsace, again for a base line near the port
of Brest, and finally in 1827 for a base line in south-west France near Dax, Borda’s birthplace. In Dax there is now a museum commemorating the life and work
of Borda.
The fifth rod, used in the pendulum
experiment, was halved in length in 1806 for pendulum measurements by Jean Baptiste Biot and François Arago (26). The 1806 experiments were combined with an
extension of the meridian survey from Barcelona to the Balearic Islands, and
in 1817, after the end of the Napoleonic wars, Biot
carried out similar work in Scotland and extended the meridian to Shetland,
publishing the results in 1821 (27). However, he did not use Lenoir’s rods
for the later surveys.
In 1856, the first rod was compared with
one made for the Spanish cartographers, but since then it has been preserved
with the others at the Paris Observatory (where they are known as ‘les règles de Borda’). They are the
largest and most elaborate platinum instruments made in the eighteenth
century and excellent examples of the results that can be achieved by the
close collaboration of scientists and skilled craftsmen.
The story does not end there, for today
the meter and the kilogram are a well accepted part of the daily life of most
people. ‘Le Système International d’Unités’ is used for measurements by scientists
worldwide, with the meter and the kilogram being two of the seven base SI
units. From these seven fundamental units, all other units of measurement are
derived.
References
1. D. McDonald and L B. Hunt, A History
of Platinum and its Allied Metals, Johnson Matthey,
London, 1982, pp. 180-181.
2. W. Hallock
and H. T. Wade, Outlines of the Evolution of Weights and Measures and the
Metric System, Macmillan, New York, 1906, p.63.
3. W. A. Smeaton,
Decimalisation: the origins, Student
Technologist, 1972, 5, 22-23.
4. C. Webster, Decimalization under
Cromwell, Nature, 1971, 229, 463.
5. W. Hallock
and H. T. Wade, op. cit., (Ref. 2), p.43.
6. R. E. Schofield, The Lunar Society
of Birmingham,
Clarendon Press, Oxford, 1963, pp. 256-257.
7. For a detailed account of the
discussions from 1789 to 1791, see Y. Noël and R. Taton,
La réforme des poids et mesures. . .1789-1791 in Oeuvres
de Lavoisier. Correspondance,
ed. P. Bret, Académie des Sciences, Paris, 1997,
Vol. 6, pp. 439-465.
8. W. Hallock
and H. T. Wade, op.cit., (Ref. 2), pp. 110-114.
9. R. Hahn, The Anatomy of a Scientific
Institution. The Paris Academy of Sciences, 1666—1803, University of California Press, Berkeley, 1971, p. 164
10.A.E. Ten, L’Académie
des Sciences et les origines du
système métrique décimal, in Mètre et Système Métrique, S. Debarbat, A. Ten, Eds., Observoire
de Paris, Paris, 1993, pp. 15-32.
11.For Lenoir’s
life and times, see A. J. Turner, From Pleasure and Profit to
Science and Security. Étienne
Lenoir and the Transformation of
Precision Instrument-Making in France 1760-1830,
Whipple Museum, Cambridge, 1989.
12. For a brief account, see A. Wolf, A
History of Science, Technology and Philosophy in the Eighteenth Century,
2nd ed., Allen and Unwin, London, 1952, pp. 78-79.
All measurements of length are in
French units:. 1 foot = 32.47 cm; 1 inch = 2.71 cm;
1 line = 0.23 cm. See also Ref 14.
13. W.A. Smeaton,
Bertrand Pelletier, Master Pharmacist. His Report on Janety’s
Preparation of Malleable Platinum’, Platinum Metals Rev., 1997,
41(2), 86.
14.For full
details of the pendulum experiments, see J.C. Borda
and J.D. Cassini, Expériences
pour connoitre la longueur
du pendule qui bat les secondes à Paris, in J.B.J. Delambre, Base
du Système Métrique Decimal, Baudouin,
Paris, 1810, Vol. 3, pp. 336-401. This work in 3 volumes
(1806, 1807, 1810), describes all relevant experiments, observations and
calculations from 1792 to 1798 by Delambre, Méchain (who died in 1804) and others
15.J.C. Borda, Expériences sur les règles qui ont servi à
la mesure des bases de l’arc
terrestre, in J.B.J. Delambre,
op.cit., (Ref. 14), Vol. 3, pp.
313-316.
16.Borda did not
mention Lavoisier’s participation, to which
attention was drawn by H.W. Chisholm, Lavoisier’s
work on the foundation of the metric system, Nature, 1874, 9,
185.
17.J.B.J. Delambre, op. cit., (Ref. 14), Vol
3, p. 676.
18.W. Hallock and H. T. Wade, op.cit.,
(Ref. 2), pp. 53-54.
19.Instruction sur
les mesures déduites de
la grandeur de la Terre, uniforme pour toute la République,et sur les calculs relatifs à leur
division décimal, Imprimerie
Nationale, Paris, An II de la République.
The date referred to the new Republican calendar, in which Year I began when
the Republic was declared on 22 September 1792. ‘An II’ (Year II) ran from 1793-1794.
20.D. McKie, Antoine Lavoisier:
Scientist, Economist, Social Reformer, Constable, London, 1952, pp. 290 –291.
21.W.A. Smeaton, French scientists in the shadow of the
guillotine: the death roll of 1792-1794’, Endeavour,
1993, 17, 60.
22.M.P. Crosland,
The congress on definitive metric standards, 1798-1799: the first
international scientific conference?’, Isis, 1969, 60, 226.
23.Letter from C.
Blagden to J. Banks, 8 September 1791: British Library, Add. MS. 33272, ff. 97-98.
24.D. McDonald,
L.B. Hunt, op. cit., (Ref. 1), pp. 295-299.
25.W. Hallock and H.T. Wade, op. cit., (Ref. 2), pp.
63-68.
26.C. Wolf, Recherches historiques sur les étalons de l’Observatoire", Ann. Chim.
Phys., Series 5, 1882, 25, 5-112 (especially: Les règles de Borda, 54-61).
27.M.P. Crosland, ‘Jean Baptiste Biot’, Dictionary
of Scientific Biography, C. C. Gillispie, Ed.,
Scribner, New York, 1970, Vol. 2, pp. l33-140 (especially pp. 135-136,
140).
28.For the
industrial exhibitions, see M. P. Crosland, The Society of Arcueil. A View of French Science at the Time of Napoleon
I, Heinemann, London, 1967, pp. 36-37.
The Author
William A. Smeaton is Emeritus Reader in History of Science at the
University of London. He formerly lectured in
chemistry at the
Northern Polytechnic
and in history of science at University College London. His main interest is science in
18th century France.
*
Reprinted with
permission from Platinum Metals Review, 2000, 44 (3),
125-134.
Note: Several figures
have been omitted
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