C 344 ] 
be juft, and that the author has himfelf fallen Into an 
equal miftake with that of which he accufes them. 
But, in order to fet this matter in a clearer light, 
it will be firft neceffary to conlider motion and time, 
relatively to each other ; tor, except this be done, it 
will be impoflible to underftand any thing precife 
from converting a certain number of minutes and 
feconds into mean folar time, or time of the Primum 
Mobile. 
There are three different kinds of time ufed by 
aftronomers, fidereal time, apparent folar time, and 
mean folar time. The interval between the tranfit 
of the firft of Aries acrofs the meridian one day, and 
its return to it the next day, is called a fidereal day, 
which is divided into 24 equal parts or hours, and 
the hours into minutes, &c. This time is fhewn by 
a clock regulated to agree with the tranlit of the ftars 
acrofs the meridian. The interval between the 
tranfit of the fun acrofs the meridian one day, and 
Ins tranfit the next day, is called an apparent folar 
day, which is divided into hours, minutes, Q 3 c. of 
apparent time. The folar day, it is manifeft, and 
its hours, minutes, & fc. are of different lengths, at 
different times of the year : on account of which 
inequality, a good clock, which keeps equal time, 
cannot long agree with the lun’s motion, which is 
unequal. Therefore, aftronomers have deviled an 
imaginary time, called mean -folar time ; which is 
what would be pointed out by the fun, if his motion 
in right afcenfion from day to day was uniform, or, 
in other words, it is what would be pointed out by a 
fi&itious fun or planet fuppofed to move uniformly 
in the equator, with a motion equal to the mean 
A motion 
