1826.] of the Length of the Pendulum at the Equator, 345 



details of the calculations are of course not inserted, as these 

 alone would occupy a very large volume. The calculations for 

 finding the specific gravity of the pendulum for the correction 

 on account of the buoyancy of the atmosphere, for the height of 

 the pendulum above the level of the sea, for finding the length 

 of the pendulum at the equator, and for the ellipticity, have also 

 been gone over by E. Lake, Esq. of the Madras Engineers, who 

 was so good as to undertake this service ; and as in nice and 

 difficult computations of this nature, the more calculators there 

 are, independent of each other, the better, 1 was much obhged, 

 and I may add gratified, by his having done so. 



I have commenced with the pendulum experiments as being 

 the most important ; the first table shows the rate of the clock 

 while those experiments were making, the same which is used 

 in the deductions. The series of eacu observer I have divided 

 into four sets ; between the second and third sets, the apparatus 

 was purposely put completely out of adjustment, and set right 

 again; between the other sets, the apparatus was examined 

 from time to time, and any trifling adjustment made that was 

 required.* 



Remark. — Great changes in the atmosphere took place, it 

 will be seen, during the time these experiments were making. 

 In the course of a day, we find the thermometer at the com- 

 mencement of the experiments in the morning at 79° or 80° ; the 

 hygrometer from 24° to 35° moist ; f and in the afternoon of the 

 same day, while the experiments were going on, the heat 

 increased to 96° or 97°, the hygrometer at the same time show- 

 ing from 30° to 48° dry ; and considerable variations, though 

 not quite to so great an extent as these, are common ; the nights 

 being generally cold with dew sometimes, and sometimes rain 

 falling : rain also fell on some of the days. 



Although the Observatory was of treble tent-cloth, and the 

 part above the apparatus covered with a large tarpaulin, it was 

 to be expected that the pendulum must have felt such changes 

 as these, and in a degree not shown, I imagine, by the instru- 

 ments used for reducing the experiments. The only corrections 

 now required are for the buoyancy of the atmosphere, and for 

 the height of the pendulum, above the level of the sea ; that for 

 the latter will be the same for all the sets, and the heights of the 

 barometer used for the former of these corrections, vary but 

 little in the four sets; but it will be seen, almost invariably, 

 when the hygrometer showed the atmosphere to be damp, the 

 vibrations in 24 hours were greater than when it was in a dry 



* The tables here referred to, which occupy 72 pages, we also omit. Edit. 



•\- It is to be regretted that Mr. Goldinghara has not stated the nature of the hygro- 

 meter he employed; as little or no use can be made of the hygrometrical observations, 

 on that account. A similar omission renders it impossible to deduce from Mr. Grolding- 

 ham's experiments on the velocity of sound, given in a former number of the AnnaU^ 

 from the Phil. Trans., the influence of the humidity of the atmosphere on sound; for 

 which it is the only datum omitted in the paper. Edit, 



