1830-40] ROYAL ASTRONOMICAL SOCIETY 69 sources of error in pendulum experiments, and having become acquainted with Bessel's researches on the correction due to the resistance of the air, he resolved to study the whole subject by new experiments performed under every possible condition of form and material in air and in vacuum. The result of this most im- portant investigation was published in the Philosophical Trans- actions for 1832. Baily next reduced Foster's observations and prepared them for publication. Including London and Greenwich, Foster had visited fourteen stations, the most southerly one being South Shetland, in latitude -62 56'. The compression of the earth deduced from the observations was 1/289-48. The result found from Sabine's experiments made in 1822-24 from Bahia to Spitsbergen was 1/288-40, but Foster's work was five times more extensive than Sabine's. The results derived from both- these series are in excellent accord with the most recent results of pen- dulum experiments. Baily's elaborate report to the Admiralty was printed at the expense of the Government, and forms volume 7 of the Society's Memoirs (1834, 37$ PP-)- The pendulum being a natural standard of length, it was inevitable that Baily's pendulum observations should lead him to inquire into the question of the British unit of length. Already in 1830 March the Council resolved that the Society ought to possess a standard scale. In 1833 the matter was put into Baily's hands, and he had a scale constructed of a novel form, less liable to those sources of error which have so often occurred in instru- ments of this kind. The form adopted was that of a cylindrical tube i- 12 inches in exterior diameter and 63 inches long, consisting of three brass tubes drawn one within the other. The division lines are cut on palladium pins let into the tube. When in use, the scale is supported on two rollers always placed under the same points. Three thermometers were let into the tube at equal distances. The scale was compared with the imperial standard yard preserved at the House of Commons, which was fortunate, since the standard yard was lost in the conflagration of the Parlia- ment building in 1834. Baily also compared the scale with two copies of the French meter belonging to the Royal Society. His lengthy " Report on the new Standard Scale of this Society " fills 150 pages of volume 9 of the Memoirs. It includes an interesting history of the standard measures of this country.* Baily's researches on the figure of the earth naturally led to others on its density. An accidental remark by De Morgan at the Council table in 1835, that the " Cavendish experiment " ought to
- For the subsequent history of this scale, see M.N., 7, 55, and 8, 83.
C/. Weld, History of the Royal Society, 2, 267. It was re-examined by Major MacMahon in 1907 (M.N., 71, 164).
