Mifcellanea Cnriofa. a 5 9 



tains, wliofe height exceedingly chills the Air 

 brought by the Winds over them ; and of the 

 Nature of the Soil, which varioufly rerains the 

 Hear, particularly the Sandy, which in Africa^ 

 Arabia, and generally where fuch Sandy Defarts 

 are found, do make the Heat of the Summer in- 

 credible to thofe that have not felt it. 



In the profecution of this firft Thought, I 

 have folved the Problem generally, to give 

 the proportional Degree of Heat, or the Sum 

 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 Sur- 

 face of a Cylindrick Hoof, or of a given part 

 thereof. 



Now this Problem is net cf that difficulty as 

 appears at firft fight, for in Tab. 4. Fig. 3. let 

 the Cylinder ABCD be cut obliquely with the 

 Ellipfe BKDI, and by the Center thereof H, de- 

 fcribe the Circle IKLM ; I fay, the Curve Sur- 

 face 1KLB is equal to the Rectangle of IK and 

 BL, or of HK and x BL or BC : And if there 

 be fuppoled another Circle, as NQPO, cutting, 

 the faid Ellipfe in the Points P, qT ; draw PS, 

 QR, parallel to the Cylinders Axe, till they 

 meet with the aforefaid Circle IKLM in the 

 Points R, S, and draw the Lines RTS, QVP 

 bife&ed in T and V. I fay again, that the 

 Curve Surface RMSQDP is equal to the Re- 

 ctangle of BL or MD and RS, or of n BL 

 or AD and ST or VP ; and the Curve Surface 



QNPD is equal to RS x MD- rhe Arch 



RMS x SP, or the Arch MS * % SP : Or it is 

 equal to the Surface RMSQDP, fubftra&ing 

 the Surface RMSQNP. So i'kewife the Curve 

 Surface QBPO is equal to the Sum of the Sur- 



S % face 



