1865.] The Proposed P end alum Operations for India. 265 



pendulum. He concluded from all his results, that even if a pendulum 

 is formed of materials having the same specific gravity, yet if it he 

 not of an uniform shape throughout, each distinct portion must he 

 made the subject of a separate computation, in order to determine the 

 correct vibrating specific gravity of the whole body, since each part 

 will he differently affected hy the surrounding air. 



The last extensive series of experiments were those taken in 

 1828-31 by Captain Henry Foster, who was sent out on a scientific 

 mission hy the Board of Admiralty. He took out with him four 

 invariable pendulums of different metals, two of Captain Kater's 

 pattern, and two of Baily's convertible pattern. These last consisted 

 of a plain straight bar, 2 inches wide, J inch thick, and 5 feet 2§- 

 inches long, having two knife edges 39.4 inches apart, but no heavy 

 bob or sliding weights, as in Captain Kater's pattern ; the synchronism 

 was adjusted by filing away at one end of the bar ; Baily's intention 

 was, that the pendulum should either be used as two different invari- 

 able pendulums, or applied as a single convertible one for absolute 

 determinations, at any station. The objection to the form is, that both 

 the knife edges must be exactly perpendicular to the bar, or error is 

 entailed, as the bar is not flexible like Kater's. Captain Foster 

 swung pendulums at all his stations, 14 in number, which were chiefly 

 in the southern hemisphere. He made a set of observations at Mr. 

 Browne's house before the voyage ; on the return of the pendulums 

 to England, they were again swung at the same place, but by Mr. 

 Baily, Captain Foster having been most unfortunately drowned in the 

 River Chagres, in February 1831, just as his mission was completed. 

 His observations were reduced by Mr. Baily, who obtained from them 

 an ellipticity of -g-g-Vy- 



About this time the Russian government sent out an expedition 

 under Captain Liitke, who used an invariable pendulum, formerly used 

 by Captain Basil Hall. He swung it first at Greenwich, and after- 1 



" body respectively from the axis of suspension : w', w", w">, . . . the weight (in air) 

 " of each body : s', s", s'", ... the specific gravity of each body determined in the 

 " usual manner. Then will the required vibrating specific gravity of the pen- 

 " dulum be 



w > d> 4. w " g" + w"' d'" + .. . 



8 = w' d' w" d" , w'" d' ' 



-7— + — //- + — -.IT— + - 



(Philosophical Transactions, 1832J 



