the proposed interval of Time, into the difference of the Sines of Meridian Altitudes, the Sum in one case and Difference in the other, shall be proportional to all the Action of the Sun during that space of time.
I fore-see it will be Objected, that I take the Radius of my Circle on which I erect my Perpendiculars always the same, whereas the Parallels of Declination are unequal; but to this I answer, That our said Circular Bases ought not to be Analogous to the Parallels, but to the Times of Revolution, which are equal in all of them.
It may perhaps be useful to give an Example of the Computation of this Rule, which may seem difficult to some. Let the Solstitical Heat in ♋ and ♑ be required at London, Lat. 51° 32'.
| 380- 2'28 | Co-Lat | |
|---|---|---|
| 23-30 | Decl. ⨀ | |
| 61-58 | Sinus = | ,8826 4 |
| 14-58 | Sinus = | ,258257 |
| Summa | 1,140931 | |
| Diff. | ,624417 |
| Diff. Ascen. | 3300-1'1. |
|---|---|
| Arch. Semid. æstiv. | 123-11. |
| Ar. Sem. hyb. 56-49. S. | 638923 |
| Arch. æstiv. mensura | 2,149955 |
| Arc. hyb. mensura | 991683 |
Then 1,140931 in ,836923 + 624417 in 2,149955 = 2,29734. And 1,140931 in 836929 - ,624417 in ,991638 = 33895.
So that