C 878 ) 
!X A Difconrfe concerning the Proportional Heat 
of the Sun in all Latitudes , with the Method 
of colleBing the fantz^ as it was read before 
the Royal Society in one of their late Meetings. 
By E» Halley. 
THere having lately arKen fome Difcourfe about that 
part of the Heat of Weather, fimply produced 
by the A&ion of the Sun ,• and I having affirmed, that 
if that were confidered, as the only Caufe of the Heat 
of the Weather, I few no reafon, but that under the 
Pole the folftitial Day ought to be as hot as it is under 
the Equinoctial, when the Sun comes vertical, or over 
the Zenith : for this reafon, that for all the 24 Hours of 
that Day under the Pole, the Sun s Beams are inclined 
to the Horizon, with an Angle of 13 \ degrees ; and 
under the Equinodtial, though he come vertical, yet 
he fliines no more then 12 Hours, and is again 12 Hours 
abfent, and that for 3 Hours 8 Min. of that 12 Hours 
he is not fo much elevated as under the Pole ; Co that 
he is not 9 of the whole 24 higher than 'tis there, and is 
1 5- Hours lower. Now the fimple A&ion of the Sun 
is, as all other Impulfes or Stroaks, more or left forcea- 
ble, according to the Sinus of the Angle of Incidence, 
or to the Perpendicular let fall on the Plain, whence 
the Vertical Ray (being that of the greateft Heat) be- 
ing put Radius, the force of the Sun on the Horizontal 
Surface of the Earth will be to that, as the Sinus of the 
Sun's Altitude at any other time. This being allowed 
for true, it will then follow, that the time of the con- 
1 tinuance of the Sun s fliining being taken for a Bafis y 
and the Sines of the Sun's Altitudes ereded thereon as 
Perpen- 
