69 
1830-40] ROYAL ASTRONOMICAL SOCIETY 
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 0 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*i2 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. 
Cf. Weld, History of the Royal Society, 2 , 267. It was re-examined by Major 
MacMahon in 1907 ( M.N., 71 , 164).