329 



Greenwich, since the erection of the new transit instrument, and as 

 computed by the solar tables of Delambre, which are used in the 

 computation of the Nautical Almanac ; with a view to the discovery 

 of the errors hi the elements of those tables. The number of obser- 

 vations from which this comparison was made is 1212, and they ex- 

 tend, with an interruption of only three months, from the end of 

 July 1816 to the end of the year 1826. The result of the compari- 

 son at first indicated the necessity of a correction of the epochs of 

 the sun's longitude, and of the longitude of the perigee, and per- 

 haps also of the equation of the centre. But upon pursuing the ex- 

 amination through a series of years, it became manifest that some 

 other source of irregularity existed, and that this could be no other 

 than an erroneous estimate of the masses of some of the planets, es- 

 pecially of Venus and of Mars. A more critical examination showed, 

 that there was also an error in the assigned mass of the moon. 



The author proceeds to state the process by which he arrived at 

 the determination of the amount of these several corrections. It was 

 found necessary in these investigations to take into account an error 

 which occurred in the tables with regard to the secular motion. It 

 results from his researches, that the epochs for 1816 and those for 

 1821 to 25 ought to be increased respectively by 4"'734 and 5"'061; 

 that of the perigee increased by 46"'3, and the greatest equation of 

 the centre diminished by 0"'84. The mass of Venus should be re- 

 duced in the proportion nearly of 9 to 8, and that of Mars nearly in 

 the proportion of 22 to 15. On a comparison of these results with 

 those which have been derived from an examination of some of Dr. 

 Maskelyne's observations, as given by Burkhardt in the Connaissance 

 des Terns, for 181 6, they are found on the whole to agree in the most 

 satisfactory manner. The principal discordance occurs in the correc- 

 tion of the place of the perigee ; a discordance which the author 

 thinks may arise either from want of correctness in the calculation of 

 the term in the motion of the perigee, depending on the square of 

 the time, or, what is more probable, from some undiscovered ine- 

 quality in the formula, which is a function of the sun's mean lon- 

 gitude. 



Experiments to determine the Difference in the Length of the Seconds 

 Pendulum in London and in Paris. By Captain Edward Sabine, 

 of the Royal Artillery, Secretary of the Royal Society. Communi- 

 cated by Thomas Young, M.D., Foreign Secretary to the Royal 

 Society, and Secretary to the Board of Longitude. Read November 

 15, 1827. [Phil. Trans. 1828, p. 35.] 



The author commences this paper by a brief statement of the ex- 

 isting state of the determinations of standards of length in the two 

 countries ; and he observes an attempt made by M. Arago in 1817 

 and 1818, to bring into immediate comparison the standards of the 

 two countries, proved inconclusive from the rates of the pendulums 

 not having been obtained with sufficient exactness. 



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