Royal Society. 79 
the fun's altitude, during his appearance above the horizon^ and 
conlequently of all his heat or action on the plane of the horizon 
in the propofed day : And this may allb be extended to the parts 
of the lanne day 5 for if the aforefaid fum of the fines of the meri- 
dian altitudes, be multiplied by half the fum of the fines of the 
fun's horary dillance from noon, when the times are before and 
sifter noon , or by half their difference, when both are on the lame 
fide of the meridian ; and if the produdl of half the arch an- 
fwerable to the piopoled interval of tim.e into the difference of the 
fiines of meridian altitudes be added thereto in fummer, or fub- 
llra61:ed therefrom in winter ; the lum in one caie, and difference 
in the other, will be proportional to the whole a6lion of the fun 
during that fpace of time: It may be objected, that the radius of 
the circle, on which the perpendiculars are ereded, is taken 
always the fame, whereas the parallels of declination are unequal; 
but to this it is anf^vered, that the faid circular bales Ihould not 
be analogous to the parallels, but to the times of revoliition, which 
are equal in all of them : It may perhaps be ufeful to give an ex- 
ample of the computation of this rule j let the folllirial heat in 
vg" and -^ be required at London^ Lat. 51° 32'. 
-8 28 Co-lat. 
2; ^o Delin.ofthefun, 
61 58 Sine =, 882^74 
14. 5S Sinerrr, 258257 
Sum 1,140931 
DifF. o,6'2 44i7 
Diff! afcenf 30 i r 
Eltival femidiurn. arch 123 11 
Hybernal femidiurn. arch ^6 49 
(Sine c? 5 892 3 
Meafure of the Eftival arch 2,140955 
Hybern. arch 0,99158$ 
Thcni, 14093 1 in 0,83^923 ^-,c;244i7 in 2, 14995 5 = 2,297 34 
And I 0,140931 in 0,83(^923 — , ^24417 in 0,991685 r=:o53;895 
So that 2,29734 will be as the tropical lummer-day's heat, 
and 0,338(^^5 as the a^ion of the fan in the day of the winter 
iolftice: After this manner, the following table is computed for 
^very roth degree of latitude, to the equinoctial and tropical fun, 
by whicli aneftimate way be made of the intermediate degrees. 
Lat. 
