The author having obtained from His Grace the Master-general of 

 the Ordnance a general leave of absence from his military duties so 

 long as he could be usefully employed in scientific pursuits, conceived 

 he could no way satisfy the condition better than in carrying into 

 effect this purpose. Accordingly, being provided with two pendu- 

 lums, one made for M. Schumacher, another the property of the 

 Boaid of Longitude, he set out for Paris, whither the pendulums were 

 forwarded to him. 



The comparison was made in Paris at the Royal Observatory, in 

 the Salle de la Me'ridienne, on the spot in which M. Biot's measure- 

 ment had been made, and every proper facility and assistance afforded 

 him. The coincidence-clock was compared every 12 h by M. Mathieu 

 with the transit-clock of the Observatory. On the 27th of April, the 

 weather having set in mild and steady, the experiments were begun. 

 The results are stated in the form of appended tables, of which a de- 

 tailed account is given. Table I. contains the daily rate of the clock 

 used for the coincidences. Table II. contains the particulars of thir- 

 teen distinct determinations of the rate of the pendulum No. 8. ; four 

 by M. Mathieu ; four by M. Nicollet ; three by the author ; one by 

 Messrs. Nicollet and Savary conjointly ; and one by M. Savary and 

 the author. They are corrected as usual. Table III. contains the 

 results of thirteen similar determinations of the rate of the pendulum 

 No. 7, in which the author was also assisted by Messrs. Freycinet and 

 Duperrey. 



Each of the pendulums, when not used in observing coincidences, 

 was employed in determining its rate by a journeyman-clock or coun- 

 ter, a method used by Messrs. Freycinet and Duperrey, but which 

 the author thinks inferior to that of coincidences, though capable of 

 giving good results. The particulars of these are given in Tables IV. 

 and V. From all these experiments in conjunction, it appears that 

 the numbers of vibrations performed in a mean solar day at Paris (re- 

 duced as usual) by the two pendulums, were respectively 85922-06 

 and 85933-83. 



The pendulums and apparatus were re-conveyed to London early in 

 September by water, and the rates again determined at Mr. Browne's 

 house in Portland Place, by means of that gentleman's excellent 

 clocks, and transit observations made by Captain Sabine. The pre- 

 cautions used are fully detailed, and the observations, which are also 

 appended in a tabular form in Tables III, VII, VIII, IX, X, XI, the 

 author being assisted by M. Quetelet, of Brussels. They give as a 

 final result 85933*29 and 85945'85 for the numbers of vibrations re- 

 spectively, made by each in a mean solar day, similarly reduced for 

 London. 



As a final result of the whole operation, the author regards 12*'00 

 as the acceleration of the seconds pendulum in passing from Paris to 

 London. The same acceleration deduced from a comparison of M. 

 Biot's and Captain Kater's direct measurements of the seconds pen- 

 dulum, in Paris and in London, comes out 11*76, or, conversely, the 

 length of the seconds pendulum observed by the former in London 



