[4] As all the scientific and technical equipment for a vast undertaking of this kind had to be created, Ibáñez, in collaboration with his comrade, Captain Frutos Saavedra Meneses, drew up the project of a new apparatus for measuring bases.

He recognized that the end standards with which the most perfect devices of the eighteenth century and those of the first half of the nineteenth century were still equipped, that Jean-Charles de Borda or Friedrich Wilhelm Bessel simply joined measuring the intervals by means of screw tabs or glass wedges, would be replaced advantageously for accuracy by the system, designed by Ferdinand Rudolph Hassler for the United States Coast Survey, and which consisted of using a single standard with lines marked on the bar and microscopic measurements.

[4][13][25] Finally, this second version of the appliance, called the Ibáñez apparatus, was used in Switzerland to measure the geodetic bases of Aarberg, Weinfelden and Bellinzona.

[17] Indeed, the southward extension of Paris meridian's triangulation by Pierre Méchain (1803–1804), then François Arago and Jean-Baptiste Biot (1806–1809) had not been secured by any baseline measurement in Spain.

[35][36] Moreover Louis Puissant declared in 1836 to the French Academy of Sciences that Jean Baptiste Joseph Delambre and Pierre Méchain had made errors in the triangulation of the meridian arc, which had been used for determining the length of the metre.

[40] This connection was a remarkable enterprise where triangles with a maximum length of 270 km were observed from mountain stations (Mulhacén, Tetica, Filahoussen, M'Sabiha) over the Mediterranean Sea.

[29] In 1866 Spain, represented by Ibáñez, joined the Central European Arc Measurement (German: Mitteleuropäische Gradmessung) at the Permanent Commission meeting in Neuchâtel.

[58][4] He received the Légion d'Honneur in recognition of his efforts to disseminate the metric system among all nations and was awarded the Poncelet Prize for his scientific contribution to metrology.

After an in-depth discussion in which an American scholar, Charles Sanders Peirce, took part, the association decided in favor of the reversion pendulum, which was used in Switzerland, and it was resolved to redo in Berlin, in the station where Friedrich Wilhelm Bessel made his famous measurements, the determination of gravity by means of devices of various kinds employed in different countries, to compare them and thus to have the equation of their scales.

[61] The reversible pendulum built by the Repsold brothers was used in Switzerland in 1865 by Émile Plantamour for the measurement of gravitational acceleration in six stations of the Swiss geodetic network.

Following the example set by this country and under the patronage of the International Geodetic Association, Austria, Bavaria, Prussia, Russia and Saxony undertook gravity determinations on their respective territories.

As the figure of the Earth could be inferred from variations of gravitational field, the United States Coast Survey's direction instructed Charles Sanders Peirce in the spring of 1875 to proceed to Europe for the purpose of making pendulum experiments to chief initial stations for operations of this sort, to bring the determinations of gravitational acceleration in America into communication with those of other parts of the world; and also for the purpose of making a careful study of the methods of pursuing these researches in the different countries of Europe.

[6][5] Under Ibáñez's presidency, the International Geodetic Association acquired a global dimension with the accession of the United States, Mexico, Chile, Argentina and Japan.

Only when this series of metrological comparisons would be finished with a probable error of a thousandth of a millimetre would geodesy be able to link the works of the different nations with one another, and then proclaim the result of the measurement of the Globe.

Although marked by the concern to correct vertical deflections, taking into account the contributions of gravimetry, research between 1910 and 1950 remained practically limited to large continental triangulations.

It performed the first great deed dictated by the motto inscribed in the pediment of the splendid edifice that is the metric system: "A tous les temps, à tous les peuples" (For all times, to all peoples); and this deed consisted in the approval and distribution, among the governments of the states supporting the Metre Convention, of prototype standards of hitherto unknown precision intended to propagate the metric unit throughout the whole world.

These prototypes were made of a platinum-iridium alloy which combined all the qualities of hardness, permanence, and resistance to chemical agents which rendered it suitable for making into standards required to last for centuries.

It was common knowledge, for instance, that effective measurements were possible only inside a building, the rooms of which were well protected against the changes in outside temperature, and the very presence of the observer created an interference against which it was often necessary to take strict precautions.

[66][57] The BIPM's thermometry work led to the discovery of special alloys of iron-nickel, in particular invar, for which its director, the Swiss physicist Charles-Édouard Guillaume, was granted the Nobel Prize for physics in 1920.

[8][70] In 1889, the French Minister of Foreign Affairs, Eugène Spuller introduced the first General Conference on Weights and Measures with these words: Your task, so useful, so beneficial to mankind, has been traversed by many vicissitudes for a hundred years.

General Morin, who has been your worthy colleague for so long, wrote a few lines on this subject that you will be proud to hear: "To brave dangers similar to those which Méchain ran with the necessary calm, it is not enough to be devoted to science and to its duties; you must have an empire over your senses which will protect you from this kind of vertigo, in the shelter of which the most intrepid soldiers are not always.

Someone who, without flinching, has faced the bullets a hundred times is, on the contrary, surprised by this insurmountable weakness in the presence of the emptiness that space offers him."

It is a soldier speaking, Gentlemen; please listen to him again when he adds: "Science therefore also has its heroes who, happier than those of war, leave behind only works useful to humanity and not ruins and vengeful hatred."

Spuller, Eugène (1889), Compte rendus de la première Conférence générale des poids et mesures (PDF), p. 8 Thanks to the determination and skill of Delambre and Méchain, the Enlightenment of science overcame the Tower of Babel of weights and measures.

[77] Nevertheless, it was an infavourable vertical deflection which gave an inaccurate determination of Barcelona's latitude and a metre "too short" compared to a more general definition taken from the average of a large number of arcs.

In 1901, Friedrich Robert Helmert determined the values of his ellipsoid of reference taking into account gravimetry work of the International Geodetic Association.

The ability of the observer consists in discovering the greatest possible number of systematic errors to be able, once he has become acquainted with their laws, to free his results from them using a method or appropriate corrections.

Therefore, the Spanish government chose the name of the peak of Mulhacén to attach forever the memory of this famous scientific achievement to the name of Ibáñez, by conferring on him the title of 1st Marquis of Mulhacén, granted, as it is said in the royal decree, " in recognition of the brilliant services which he rendered during his long career, directing with rare talent the Geographical and Statistical Institute of Spain, and contributing to the prestige of Spain among the other nations of Europe and America ".

Following a report by Gustave Ferrié, the Bureau des Longitudes organized at the Paris Observatory a Conférence internationale de l'heure radiotélégraphique in 1912.

In 1936, irregularities in the speed of Earth's rotation due to the unpredictable movement of air and water masses were discovered through the use of quartz clocks.