39 4* Afr. Gilpin’s Observations on the Variation, 
of variation was found about the year 1775 to be nearly io'; 
and was considered at that time to be gradually diminishing, 
but it is remarkable that this rate of increase appears from the 
annexed Table to be nearly the same at which it has been found 
to move between all the different periods in the said Table, from 
1580 to 1787, a period of more than 200 years, excepting 
between the years 1692 and 1723; the observations of Dr. 
Halley in 1692 and Mr. Graham in 1723 make the annual 
increase 16 ' ; to what this difference could be owing I am at a 
loss to account; on referring to observations made at Paris for 
those two years the annual increase is 14,' ; subsequent observa- 
tions made by Mr. Graham in 1748 make the annual increase 
between this year and 1723 only 8',i nearly what its rate had 
been found before this great difference occurred ; and from 
the variation of Mr. Graham in 1748, and the variation ob- 
served by Dr. Heberden in 1773, the annual increase is 8', 4; 
the variation in 1773 compared with the variation observed 
by myself in 1787, give for the annual rate of increase 9', 3; 
but between 1787 and 1 795, the annual increase was only 
4', 7; between 17 95 and 1802, i ; ,2 ; and between 1802 and 
1805, only o', 7. 
The mean rate of annual increase for the above mentioned 
period of 207 years, viz. from 1380 to 1787, is 10'. 
As there appears something curious in the rate at which 
the variation has been moving from observations made at 
London, for a period of more than 200 years, the annual 
increase of which during that time continued nearly the same, 
but in a subsequent period of 1 8 years only, the decrease of 
that annual increase became so rapid, that the annual increase 
in the latter part of it does not amount to quite one minute* 
