i to Mr . hemchel’s Aftroncnucal Qbfervatlons 
Mars to as great an exaCtnefs as we jfhall think necelfary for the 
purpofe of our comparative view. 
Had fuch obfervations as thefe been made two thoufand, or 
perhaps only fo many hundred years ago, we might now, by 
repeating them, moft probably become acquainted with fome 
curious minute changes of the folar fyftem that have hitherto 
palled unnoticed. 
There is a certain circumftance which would almolt create a 
fufpicion that there has been fome retardation in the diurnal 
motion of the earth. The difference between the equatorial 
and polar diameters of the earth, by aCtual meafurement, has I 
been found to be about 36 Englifh miles and 9 tenths ; but, by ! 
a calculation wherein the prefent rotation is made ufe of, it ; 
will only amount to about 33 miles and 8 tenths : from which 
it fhould feem probable, that when the earth afliimed the prefent ; 
form, the diurnal rotation was fomewhat quicker than it is at 
prefent, by which means the centrifugal force bore a greater 
proportion to the force of gravity to which it is contrary, and 
thus occafioned a higher elevation of the equatorial parts. But 
I would not lay much ftrefs upon this argument ; for, in the cal- | 
culation, it has been fuppofed, that the earth is nearly of an 
equal denfity at the furface and towards the center, which it I 
feerris is not agreeable to fome late curious experiments and : 
calculations that have been made Under the conduct of the | 
Aftronomer Royal upon the attraction of a mountain *, the 
refult of which ought now to be taken into confideration, and 
the calculation repeated* If all the data could be exactly de- 
pended upon, it would be practicable enough from 'the laws of 
* See Mr. HtrTT0N*3 Account of the Calculations made from the Survey and 
Meafures taken at Schehallien, in order to afcertain the mean Deniity of the 
Earth. Phil. Tranf 1778* 
3 gravity* 
