230 lioyal Astronomical Society. 



member of the grauwacke. It is also shown that this chain, though 

 it passes in one yart of its course within three miles of those disturb- 

 ances, still preserves in an unbroken line its true strike and direction, 

 as if unaffected by those subsequent convulsions of the coal measures. 



ROYAL ASTRONOMICAL SOCIETY. 



November 8, 1833. — The following communications were read:— 



I. Report on Captain Foster's Pendulum Experiments. By 

 Francis Baily, Esq. 



During the recess, Mr. Baily has presented to the Council his 

 Report on the Pendulum Experiments made by the late Captain 

 H. Foster, which Report has been approved by the Council, and 

 forwarded to the Lords Commissioners of the Admiralty, at whose 

 request the inquiry was undertaken. Their Lordships have since 

 been pleased to order the same to be printed at the public expense, 

 and it will form a part of the seventh volume of the Memoirs of this 

 Society. The following is a brief abstract of the contents of the 

 Report. 



Captain Foster took out with him four different pendulums, two 

 of which were of the kind called Kater's invariable pendulum; but 

 the other two were of a new construction, recommended by Mr. 

 Baily, the one of iron and the other of copper, each of which was 

 furnished with two knife-edges ; so that, in fact, Captain Foster 

 might be considered as having taken out six different and inde- 

 pendent pendulums. The iron and copper pendulums are the pro- 

 perty of this Society : the brass ones belong to Government. The 

 places at which Captain Foster swung these pendulums are fourteen 

 in number: viz. London, Greenwich, Monte Video, Staten Island, 

 South Shetland, Cape Horn, Cape of Good Hope, St. Helena, 

 Ascension, Fernando de Noronha, Maranham, Para, Trinidad, and 

 Porto Bello. At all these places (with the exception of the experi- 

 ments with one of the brass pendulums at South Shetland,) the re- 

 sults are very accordant, and show that the pendulum, even with 

 its present imperfections, affords an accurate measure of the relative 

 force of gravity at different latitudes. But Mr. Baily has detected 

 some minute sources of error in this instrument which were never 

 before suspected, and an attention to which will render future ex- 

 periments much more valuable, and comparable with each other. 



As it would be impossible in a short abstract, like the present, to 

 enter into a comparative examination of the results at each place, 

 it will be sufficient here to state the general result of all the six pen- 

 dulums, at the several stations above mentioned. For the purpose 

 of deducing these results with the least probable chance of error, 

 Mr. Baily has adopted the usual method of minimum squares ; 

 whereby he finds that if we make 

 v = the number of vibrations at the equator, 

 g = the increase of the force of gravity, 

 L = the latitude of any other place on the globe, 

 V = the number of vibrations made by the same pendulum there, 

 the general formula 



