FIFTH REPORT- 1835. 
132 
The computed results of the preceding observations are given 
in Table II. The first and second columns contain the place 
and the date of the observations; the third the name of the 
needle employed; in the fourth column is given the mean time 
of 100 vibrations, corrected for temperature and for the rate of 
the chronometer; and the fifth and sixth columns contain the 
computed values of the horizontal intensity;—the numbers in 
the fifth column being the ratios of the horizontal intensity at the 
place of observation to that at the station of the observer, and 
those in the sixth being the ratios of the same force to that at Lon¬ 
don, to which place all the observations are ultimately referred. 
If T denote the reduced time of 100 vibrations at any place, and 
T' that at the station with which it is immediately compared, and 
if h and h! be the horizontal intensities at the two places, the 
numbers of the fifth column are computed from the formula 
A _ ( A V 
h! ~ \ T J* 
Again, if h i denote the horizontal intensity in London, the ratio 
h f 
-7-will be determined in the same manner; and, multiplying bv 
h ‘ h 
it the numbers in the fifth column, we obtain the values of-y-, or 
A 
the ratios of the horizontal intensity at the places of observation 
to that at London, as given in the sixth and last column. 
The stations with which all the other places in Ireland are 
immediately compared are Dublin and Limerick; and it will at 
once appear that, as the ratios of the horizontal force at these 
stations to that at London enter as factors in all the final results, 
much accuracy is required in their determination. For this pur¬ 
pose we have three distinct series of observations. In the first 
and second the intensities of the horizontal force in Dublin and 
Limerick are directly compared with that in London ; and in the 
third these intensities are compared together. The results of 
these comparisons, given in Table II., are here put together, so 
as to be seen at one view. 
I. Horizontal intensity in Dublin, the horizontal intensity in 
London being unity. 
July, Aug. 1835. Cyl. R (c).Int. = *9456 
. “ . — R (d) . — 9421 
September, 1835 . — L (a). —- ‘9390 
——... — L ( b ). — -9376 
Oct., Nov., 1835. — L (a). — ’9319 
.. _ L ( b ). — *9319 
Mean == *9380 
