128 



lenses, on cylindrical rods, on bars, on tabes, on convertible pendu- 

 lums, and on several clock pendulums, amounting to upwards of 40 

 in number. The results of these experiments give in each case a 

 different value for the factor n ; and which appears to depend on the 

 extent of surface, in proportion to the bulk of the body exposed to 

 the direct action of the air when in motion : further experiments, 

 however, are requisite to establish this point in a satisfactory manner*. 

 But, in the author's opinion, enough is shown to indicate the neces- 

 sity and propriety of a revision and correction of all the experiments 

 hitherto made with the pendulum, either for the determination of its 

 absolute length, or for ascertaining the true figure of the earth ; and 

 that for this purpose, the true correction must be found from actual 

 experiment in each particular case; since, with very few exceptions, 

 it cannot be determined by any mathematical deduction. 



Mr. Baily then proceeds to point out some singular discordances 

 arising from the knife-edge mode of suspending the pendulum, where 

 the same knife-edge and the same agate planes are employed. From 

 which he is led to infer that the pendulum furnished with a knife-edge 

 and agate planes, as at present constructed, is a very inadequate in- 

 strument for the delicate purposes for which it was originally intended; 

 and that a more rigid examination of that part of the instrument is 

 requisite, before we can rely with confidence on the accuracy of the 

 results obtained by it. 



Some anomalies are then pointed out in the magnitude of the arc 

 of vibration, and some remarks offered on the supposed inadequacy of 

 the usual formula for determining the correction for the arc; but the 

 author considers it desirable that further experiments should be made 

 for the more accurate determination of this point. 



In conclusion, the author expresses a doubt of the rigid accuracy 

 of the length of the seconds pendulum, as deduced from the recent 

 experiments of Captain Sabine. 



To the whole are appended tables exhibiting the details of all the 

 experiments made by the author, and the corresponding results. 



A Paper was read, entitled, " Researches in Physical Astronomy," 

 by John William Lubbock, Esq. V.P. and Treas. R.S. 



The present paper contains some further developments of the 

 theory of the moon, which are given at length, in order to save the 

 trouble of the calculator, and to avoid the danger of mistake. The 

 author remarks, that while it seems desirable, on the one hand, to 

 introduce into the science of physical astronomy a greater degree of 

 uniformity, by bringing to perfection a theory of the moon founded on 

 the integration of the equations employed in the planetary theory, it 



* Since this paper was read, the author has made a number of addi- 

 tional experiments on various other pendulums, which, by permission of 

 the Council, will form part of the original paper; and from which he is 

 led to infer that, in the case of spheres, cylinders, and other bodies sus- 

 pended by rods of different diameters, the value of the factor depends not 

 only on the body appended to such rod, but that the rod itself has a con- 

 siderable influence on the result, except it be a very fine wire; when its 

 effect becomes merged in that of the appended body. 



