386 Capt. Kater’s experiments for determining the variation 
longitude of Portsoy io".39*,o9 west of Greenwich. The 
mean of this, and the preceding result being is 
perhaps not many seconds distant from the truth. I must 
however remark, that from the variation in the rate of the 
chronometer, I do not rely upon these longitudes beyond the 
purpose to which they are to be applied, that of finding the 
sun’s declination at apparent noon. 
The instrument used for determining the latitudes, was the 
repeating circle, of one foot diameter, mentioned at the com- 
mencement of this Paper. Of the power of the repeating 
circle I had ever entertained the most favourable opinion; 
and I had now an opportunity of bringing it to the test of ex- 
periment, by connecting my stations with those of the trigo- 
nometrical survey, and comparing the latitudes obtained by 
the repeating circle with those deduced from observations 
made with the zenith sector. 
As an error in latitude amounting to one minute, would not 
occasion a difference of one tenth of a vibration of the pendu- 
lum in 24 hours, I conceived it would have been an expense of 
time, which I could ill afford, to have waited for multiplied 
observations, except at certain stations, the latitudes of which I 
was anxious to ascertain with particular accuracy. 
By the mean of numerous readings, I found the correction 
for the index error of my instrument to be -f- 18"; and the 
value of each division of the large level to be 2 ,"4. 
In order to deduce the meridional zenith distance, from 
observations made near the meridian, I availed myself of a 
very convenient formula, for which I was indebted to Dr. 
Young, and which has since been published, together with a 
small table of verse sines, by order of the Commissioners of 
