ON THE ELLIPTICITT OF THE EAETH. 473 



the years 1828 1831, which, on account of the unity of 

 the observer, the identity of the instruments, the num- 

 ber of stations, and the extent of the arc which they 

 embrace, must undoubtedly be considered to hold the 

 first place in the determinations of that hemisphere. In 

 January, 1828, a communication was received by the 

 Royal Society from H.R. Highness the Duke of Clarence 

 (afterwards King William the Fourth), then Lord High 

 Admiral, intimating the favourable disposition of Go- 

 vernment to extend to the southern hemisphere the 

 investigation into the figure of the earth which had 

 been recently completed in the northern hemisphere ; 

 and requesting from the Royal Society such suggestions 

 as might be made the basis of the instructions to be 

 given to the officer who might be selected to execute 

 them. The reply was drawn up by a committee of the 

 Royal Society, of which Sir John Herschel was chairman, 

 and of which I was myself a member, and is preserved 

 in the archives of the Royal Society. Captain Foster, 

 who was appointed to conduct the experiments, had 

 been a midshipman with Captain Basil Hall, in the 

 " Conway," and afterwards with Captain Clavering, in 

 the " Griper," in which ship I was then visiting Spitz- 

 bergen and Greenland, and had recently received the 

 Copley medal of the Royal Society for his researches in 

 several branches of physical science made during the 

 arctic voyages of Sir Edward Parry in 1824 25 and 

 1827. The "Chanticleer" sloop of war having been 

 commissioned expressly for this service, Captain Foster 

 sailed from England in the spring of 1828, and in the 

 course of the two following years completed the experi- 



