J. H. Gore — Decimal System of Seventeenth Century. 27 



foot — a length given him by Auzout — made 2140*4 vibrations 

 in half an honr, from which he concluded that the length of 

 the seconds pendulum would be 36 inches 6*3 lines. That 

 caused me to examine the matter very carefully while I was at 

 Lyons, using for this purpose a large clock such as I had used 

 elsewhere ; and after all, I remained convinced that the true 

 length of the second's pendulum at Lyons was 36 inches, 8*5 

 lines. 



This application of the pendulum evidently pleased Picard, 

 as in the same report he adds : if one had found the length of 

 a seconds pendulum expressed in the usual measures of each 

 country, one could know the relations of these measures as if 

 they had been directly compared with one another, — besides 

 this, one could detect at any time in the future a change in 

 their lengths. These universal measures suppose that a change 

 of locality produce no appreciable variation in the length of 

 the pendulum ; it is true that experiments have been made at 

 London, Lyons, and Bologna, which seem to show that the 

 pendulum shortens as the equator is approached, . . . but we 

 are not sufficiently informed as to the accuracy of these observa- 

 tions to deduce any conclusions from them. Picard did not 

 care to endorse the possibility of this shortening of the pendu- 

 lum, it would have tended to corroborate the oblate spheroid 

 hypothesis, which at this time was not at all popular at Paris. 

 In 1733, Mouton sent to the Academy at Paris, a copy of the 

 trigonometric tables which he had computed. In the note of 

 acknowledgment, he is referred to as very well known by his 

 work on the diameters of the sun and moon, and is called 

 "habile dans les mathematiques." 



As late as 1776 de la Condamine says : M. Mouton, priest at 

 Lyons, was the first, whom I know, to propose a unit deducibie 

 from the pendulum ; this was in 1670. He adds that it was 

 proposed by Mouton in 1668 (it should be 1665), adopted 

 by Picard in 1672, and by Huygens in the same year. 



Cassini, in 1757, refers to Mouton as one whom we know 

 only as a priest and master of the choir at the collegiate church 

 of St. Paul. Perhaps this is simply to prevent people from 

 supposing that his own scheme was not taken partly or wholly 

 from Mouton. He proposed to take one six-millionth part of 

 a minute of a terrestrial arc and call it a foot. He also sug- 

 gested that the unit be a toise, 60,000 toises being contained in 

 a degree. This was simply taking one-thousandth of a minute, 

 which was Mouton's identical plan. 



Thus it is seen that Mouton's idea was never lost sight of. 

 He was quoted often enough, and by such men as to keep his 

 views from being forgotten, but when we come to that monu- 

 mental work which recounts the incentives, beginnings, meth- 



