[ 345 ] 
motion of the fun in longitude, its diftance from the 
firft point of Aries (meaning hereby the mean equi- 
nox) being always equal to the mean longitude of 
the fun : and as apparent noon is the inftant of the 
true fun’s coming to the meridian, fo mean noon is 
the inftant at which this fi&itious planet would come 
to the meridian. The interval between its coming to 
the meridian on any two fucceftive days is a mean 
folar day, which is divided into hours, minutes, &c, 
of mean folar time ; all which it is manifeft will pre- 
ferve the fame length at all times of the year. 
The equation of time, at the inftant of apparent 
noon, or of the fun’s pafling the meridian, being 
equal to the difference between mean time and 12 
hours, is alfo equal to the interval between the mean 
and true fun’s pafting the meridian expreffed in mean 
folar time : to find which, we have the diftance of 
the mean fun from the meridian, at the inftant of 
apparent noon, equal to the difference between the 
fun’s apparent and mean right afcenfton (both reckoned 
either from the mean or apparent equinox) which 
may be called the equation of right afcenfion. The 
queftion, therefore, comes to this, How many mi- 
nutes and feconds of mean folar time doth the mean 
fun take to move this diftance up to or from the 
meridian ? Aftronomers hitherto have allowed 1 mi- 
nute of time to every 1 5 minutes of right afcenfion, 
and fo in proportion ; and, I apprehend, juftly too; 
for does not the mean fun, in returning to the me- 
ridian, defcribe 360° about the pole in 24 hours of 
mean folar time ; whence it is plain, that his depar- 
ture from the meridian is at the rate of 15 0 to 1 
hour, and 15' to 1 minute of mean folar time. 
Vol. LIV. Y y Therefore 
