400 
MR. BAILY ON THE CORRECTION OF 
immediate neighbourhood of the pendulum ; and has even imagined that the 
results may be affected by an increase of buildings in the vicinity. But, to 
whatever cause the observed anomalies may be owing, I must confess that I 
have myself, during a long course of experiments on various pendulums, at 
different seasons of the year, and under a variety of circumstances, frequently 
met with discordancies that have baffled every attempt at explanation by any 
of the known laws applicable to the subject: and I believe that other persons 
also, who have had much practice in pendulum experiments, have occasionally 
met with anomalies for which they have been unable to account satisfactorily. 
As it is desirable, however, that these difficulties should be cleared up if pos¬ 
sible, and as every information connected with so important a subject, founded 
on such delicate experiments, must add to our means of removing them, I 
trust I need not apologize for drawing the attention of this Society to the re¬ 
sults of some experiments, made with pendulums of various forms and con¬ 
struction, immediately bearing on the discordancies in question. 
In fact, till we can construct two pendulums, that will always tell precisely 
the same tale, cleared of all these discordancies, the important problem of the 
determination of the length of the seconds pendulum cannot be considered as 
fully solved: neither can the observations of different experimentalists, in dif¬ 
ferent parts of the globe, with different pendulums, be strictly and directly 
comparable with each other. It is true that we have two pendulums, in form 
and construction totally different from each other, whose results have been 
closely compared : viz. Borda’s pendulum, and Rater’s convertible pendulum. 
But, although the great accordance in those results, by two such different 
means, evince the talent and skill of the distinguished persons engaged in 
making the experiments ; yet it should now be borne in mind that the reduc¬ 
tions to a vacuum were, in both cases, made agreeably to the old formula: 
and that, since M. Bessel’s important investigations on this subject, which 
indicate the necessity of revising the computations of all preceding experi¬ 
ments, no rigid comparison of the results has yet been repeated. The amount 
of the additional correction, for the two respective cases, varies materially, as 
I shall more fully show in the sequel: so that we are, in fact, at the present 
moment, totally ignorant whether the results of any two pendulums that have 
ever yet been constructed, are in strict and reasonable accordance with each 
