C 880 ) 
tion imprefs'd by the paft A&ion of his Rays wherein 
Heat confifts, before he arife again: But under the Pole 
the long abfence of the 0 for 6 Months, wherein the 
extremity of Cold does obtain, has fo chill'd the 
Air, that it is as it were frofen, and cannot, before the 
Sun has got far towards it, be any way (enfible of his 
prefence, his Beams being obftru&ed by thick Clouds, 
and perpetual Foggs and Mills, and by that Atmojphere 
of Cold, as the iate Honourable Mr. Boyle was pleafed 
to term it, proceeding from the everlafting Ice, which 
in immenfe Quantities does chill the neighbouring Air, 
and which the too foon retreat of the Sun leaves unthaw- 
edj to encreafe again, durijig the long Winter that fol- 
lows this Ihort Interval of Summer. But the differing 
Degrees of Heat and Cold in differing Places, depend in 
a great meafure upon the Accidents of the Neighbour- 
hood of high Mountains, whole height exceedingly 
chills the Air brought by the Winds over them ; and 
of the nature of the Soyle, which varioufly retains the 
Heat, particularly the Sandy, which in Africa, Arabia, 
and generally where luch Sandy Defarts are found, do 
make the Heat of the Summer incredible to thole that 
have not felt it. 
In profecution of this firft Thought, I have folved the 
Problem generally, viz. to give the proportional degree 
of Heat or the fum of all the Sines of the Sun's Altitude, 
while he is above the Horizon in any oblique Sphere, 
by reducing it to the finding of the Curve Surface of a 
Cylindrick Hoof, or of a given part thereof. 
Now this Problem is not of that difficulty as appears 
at firft fight, for in Fig, 9. let the Cylinder ABCD be 
cut obliquely with the Ellipfe BKDI, and by the centre 
thereof H, defcribe the Circle IKLM ; I (ay, the Curve 
Surface IKLB is equal to the Re&angle of IK and BL, 
or of HK and 2 BL or BC: And if there be fuppofed a- 
nother Circle, as NQjPO, cutting the laid Ellipfe in the 
points 
