A PENDULUM FOR THE REDUCTION TO A VACUUM. 
461 
have thought of verifying the suspicion of Newton that such an effect was pro- 
bable *. M. Prony, in his Nouvelle Architecture Hydraulique, and Dr. Young, 
in his Lectures on Natural Philosophy (both of whom have taken an active 
part in the investigations relative to the pendulum) make frequent allusions to 
Du Buat’s work : yet neither of these distinguished mathematicians appears 
to have recollected the singular facts recorded by that author. And even in 
M. Poisson’s late excellent memoir, inserted in the Connaissance des Terns for 
1834, although in the Appendix thereto the author’s attention has been called 
to M. Du Buat’s experiments by a notice from another quarter, yet it is evi- 
dent that when that distinguished mathematician commenced his paper, he was 
not aware of the facts stated in M. Du Buat’s work : as he frequently, and 
very justly, alludes to M. Bessel as the first person who had directed the 
attention of the public to the true correction. And it certainly is but a poor 
consolation to the practical philosopher, who thus devotes so much of his time 
to the elucidation of any particular branch of science, to find that his labours 
may be so soon forgotten, and probably lost sight of for ever. 
Suspension over a Cylinder. 
The principal portion of M. Bessel’s experiments on the pendulum were 
made by suspending the sphere, by means of a wire, over a steel cylinder not 
more than "088 of an inch in diameter. Being desirous of pursuing the same 
plan with respect to some of the pendulums which are the subject of this paper, 
I suspended the lead and ivory spheres (No. 8 and 9) in this manner ; the 
results of which have been already stated. I proceeded in a similar manner 
with some of the other pendulums ; but in the course of the experiments I dis- 
covered some anomalies, for which I could not at first satisfactorily account ; 
and at length found that they proceeded altogether from the mode of suspension. 
In the long cylindrical rod (No. 21) the discordancies were the most apparent : 
for not only would the intervals of consecutive coincidences differ from one 
another as much as 60, 70 and in one case as much as 90 seconds (plus and 
minus), but the arc also would be continually varying in magnitude in a similar 
manner, alternately diminishing and increasing. With a view to discover the 
cause of these singular anomalies, I erected an apparatus for more minutely 
* Principia, lib. ii. prop. 27. cor. 2. 
MDCCCXXXII. 3 O 
