第4章 A Few Words About the Metre

From all time,it may be asserted,the idea of one universal andinvariable standard of measurement,rigorously laid down by Nature herself,has existed in the mind of man,a measurement which would always be present,whatever might be the cataclysms of which the earth was the scene.Such certainly was the idea of the ancients,but they lacked methods and instruments sufficiently accurate to effect this.

The best method,in fact,of obtaining an immutable system of measurement was to relate it to the terrestrial spheroid,whose circumference may be considered as unchangeable,by measuring the whole or part of this circumference.

The ancients had attempted to determine this measurement.According to certain savants of his period,Aristotle,in the time of Sesostris,considered the stadium,or Egyptian cubit,as forming the hundred-millionth part of the distance of the Pole from the Equator.Eratosthenes,in the time of the Ptolemies,calculated fairly approximately the value of a degree along the Nile,between Syene and Alexandria.But neither Posidonius nor Ptolemy could carry out such geodesical operations with sufficient accuracy.This was also true of their successors.

Picard was the first who began in France to regulate the methods used to measure a degree;and in 1669,when determining the length of the celestial and terrestrial arcs between Paris and Amiens,he gave a degree the value of fifty-seven thousand and sixty toises(fathoms).

It was especially the French savants who had devoted their attention to this delicate operation.It was,moreover,the Constituent Assembly which,in 1790,at the suggestion of Talleyrand,passed a decree by which the Academy of Sciences was charged with the task of discovering an invariable unit of weights and measures.

‘A report signed by the illustrious names of Borda,Lagrange,Laplace,Mounge,and Condorcet proposed as a unit for measuring length the ten-millionth part of a quarter of the meridian;and for unit of weight,that of distilled water,the decimal system being adopted to correlate all these measures.

Later determinations of the value of a degree were made in several parts of the world;for as the globe is not a spheroid but an ellipsoid,repeated operations were needed to determine its polar flattening.

In 1768,for example,the astronomers Mason and Dixon,in North America,on the boundary of Maryland and Pennsylvania,estimated at fifty-six thousand eight hundred and eighty fathoms the length of the American degree.

From the various measurements taken,it may be concluded that the average value of the degree is fifty-seven thousand toises,or twenty-five old French leagues;and multiplying by this average value the three hundred and sixty degrees of the earth’s circumference,it is found that the earth measures nine thousand leagues round.

But the measurements of the various arcs obtained in different parts of the world do not absolutely agree.Nevertheless,it was from this average of fifty-seven thousand fathoms for the measurement of a degree that the value of the‘metre’was taken:the ten-millionth part of the quarter of the terrestrial meridian,about 39.37 inches.

The metre thus decided upon was not,however,adopted by all civilised nations.Most of them accepted it almost at once;but,notwithstanding the obvious superiority of the metric system over all others,England has declined to adopt it to this day.

But for the political complications which marked the close of the eighteenth century,this system might have been accepted by the people of the United Kingdom.When,on 8th May,1790,the Constituent Assembly laid down its decree,the Fellows of the Royal Society were invited to join the French savants.To measure the metre they had to decide whether it should be based on the length of a simple pendulum which beats the sexagesimal second,or whether they should take as the unit of length a fraction of one of the great circles of the earth.But events prevented this meeting from taking place.

It was only in 1854,that England,which had long realised the advantages of the metric system,and seeing the societies of learned as well as business men were being formed to urge this reform,decided to adopt it.

But the English Government was anxious to keep this resolution secret until the new geodesical operations which it was then undertaking would allow it to ascertain with the greatest possible exactitude the value of the terrestrial degree.With this object in view,the British Government thought it advisable to come to an understanding with the Russian Government,which was also leaning towards the metric system.

A commission,composed of three English and three Russian astronomers,was chosen from the most distinguished members of the scientific societies.Colonel Everest,Sir John Murray,and William Emery were selected by England;Messrs Matthew Strux,Nicolas Palander’and Michel Zorn by Russia.

This commission,at their meeting in London,first decided that the measurement of an arc of the meridian should be taken in the southern hemisphere;then that another arc should be measured in the northern hemisphere.From the result of these two operations,it was hoped to determine a most accurate value which would fulfil every necessary condition.

It then remained to choose among the various English possessions in the southern hemisphere—the Cape,Australia,or New Zealand.New Zealand and Australia,at the antipodes of Europe,would force the commission to make a very long voyage.What was more,the Maoris and the aboriginal Australians,always at war with their invaders,might make the projected operation very difficult.

Cape Colony,on the contrary,offered several real advantages.It was situated under the same meridian as certain parts of Russia-in-Europe;and,after having measured an arc of the meridian in South Africa,the commission could measure a second arc of the same meridian in the Czar’s empire,while keeping the operation secret.Secondly,the voyage to the British possessions in Southern Africa was relatively short.Finally,these English and Russian savants would have an excellent opportunity of verifying the accuracy of the French astronomer,Lacaille,who had worked in the same region,and of ascertaining whether he had been correct in giving fifty-seven thousand thirty-seven toises,or fathoms,as the measure of a degree of the meridian at the Cape of Good Hope.

So the Cape was chosen for this operation.The decision of the Anglo-Russian Commission was approved by the two Governments.The necessary funds were provided.The trigonometrical instruments needed were supplied in duplicate.The astronomer William Emery was directed to make arrangements for an exploring party into the interior of South Africa.The Augusta frigate was ordered to convey the members of the commission and their escort to the mouth of the Orange River.

But it must be pointed out that,in addition to the purely scientific questions,there was one of national amour propre which spurred on these savants thus united in a common task.It was,in fact,a question of outdoing France in her calculations,of exceeding in accuracy the labours of her most illustrious astronomers,and that,too,in the midst of a savage and almost unknown country.

Thus the members of the Anglo-Russian Commission had decided to sacrifice even,if need be,their lives to obtain a result satisfactory from a scientific point of view,and at the same time glorious for their country.

And this was why,in late January,1854,the astronomer William Emery found himself waiting at the Morgheda Falls on the banks of the Orange River.