4 Lieutenant Foster's account of 
The difference of the results amounts only to 9 ten-thousandths 
of a vibration in 24 hours. 
This, it may be observed, is the end and object of the 
problem ; which, as I have before stated, is strictly a com- 
parative one ; and the only thing to be insisted upon is, that 
the same method should be followed, and the same adjustments 
of the apparatus strictly adhered to, at all the stations which 
are to be compared together. 
Supposing, however, that the vibrations recorded in the 
present experiments, ascertained by the one method, were 
compared with those determined by the other, the results 
would differ only 0,14 of a vibration in 24 hours ; a quantity 
which does not occasion a difference of two ten-thousandths 
of an inch in the length of the deduced seconds' pendulum, 
nor of an unit in the denominator of the fraction expressing 
the ellipticity. 
There are cases, of course, dependant on the relative dia- 
meter of the white disk, to that of the tail-piece of the 
pendulum, in which a greater or less difference than the 
above would exist between the two methods so compared ; 
but this is of no importance whatever, as the object of the 
problem is fully accomplished by adhering to the same method, 
whichever it be, at both stations, as before stated. It may 
not be useless to mention also, that Captain Kater did not 
adopt the method of disappearances in his comparative expe- 
riments, until after innumerable trials of other plans, includ- 
ing that of taking the mean of disappearance and re-appear- 
ance of the white disk ; all of which he eventually abandoned 
for that of disappearances alone ; and it is certainly to be 
regretted, that he did not publish an account of these unsuc- 
