Suppose it should be made for the Slowest to Revolve in about five Days, and after it has gone just two Days, the Slowest Index should then point between 39 and 40, and the Swiftest to 21.5. Then both these Numbers (as set in Order) will make 3921.5. And if the Sun be in its Mean Motion (if not, you must Add or Substract, as aforesaid) then the said Numbers 3921.5 must always be the First; the said two Days, or 48 Hours, the Second; and the two Numbers pointed to by the Indexes, at the time for which you would find the Hour and Minute of the Day (as suppose the slow one should point to 87, and the swift one to 65.2, both making 8765.2) must be the Third; by which the Fourth will be obtained as followeth: Which Fourth Number being Divided by 12, the Remainder will be the Hour and Minute of the Day at London, as was required.
| Hours | Hours. | |||||||||||
| As | 3921.5 | : | 48 | :: | 8765.2 | : | 107.18 | |||||
| ho. | min. | } | Requir’d | |||||||||
| Remains | 11 | : | 10.8 | } | ||||||||
| hours. | } | |||||||||||
| or 11¹⁸⁄₁₀₀ | } | |||||||||||
And so for any quantity of time less than one Revolution.
But if the time required to find the Hour and Minute at London, (when at Sea or Land,) be some Weeks or Months, after it was first set going; or (if cleansed) after it was last Cleansed; then you must add 10000.0 to what the two Indexes do shew, for each Revolution, that it has made, since it was so set going, or last cleansed. And if you would at any time know how many such Revolutions must be added, to what is shewn by the Horologe; you must first note the Day of the Month, that you are then seeking the Hour for; as suppose Novem. 12. 1715. After which note the Day last entred, when cleansed; as suppose Sept. 5. 1715. Then compute the number of Days between Sept. 5. and Novem. 12. which is 25, 31, and 12, In all 68. After which observe the Time last spent in one Revolution; which you see was 5 Days, 4 Hours, and ⅛ (for which set down ⅒ for ’twill make no sensible Difference) and having thus done, say,
| Days | Hours | Hours | Revo. | Days | |||||||
| As | 5 | 4⅛ | equal to | 124.1 | : | 1 | :: | 68 | : | 13. | whole Revolutions; |
For which, as before directed, you must add 13 times 10000.0 to the Numbers pointed to, by the two Indexes: Which if we suppose 3752.2 making in all 133752.2 will be the Number required, for the 12ᵗʰ of November, if the Indexes should both point as before proposed. And having now found this Number, you are prepared to find the Hour and Minute at London, in manner following (viz.) suppose you are in or near 44 Degrees of Latitude, in the Autumn Season. Then seek the Latitude 44 Deg. and the Season Autumn, in the Book that is peculiar to your Movement, and having found both, take the Numbers Answering thereunto, which (in this Example) is 29274.2 and 240 Hours; and then say,
| Hours | Hours | ||||||
| As | 29274.2 | : | 240 | :: | 133752.2 | : | 1096.84 |
Which being devided by 12, leaves remaining 4.84 ho. or 4 ho. 50.4 min. required, for the Hour and Minute at London, by which the Longitude will be found, as before directed.
And seeing it was near the Winter Season: If you should add the Autumn and Winter Numbers, and Hours respectively together; and make them the two first Numbers in your Proportion; it would Æquate the Seasons more exactly: I mean, if the said Numbers had been really entred from Practice; but these are only supposed. And by this method you may Æquate the Numbers for finding the true Hour and Minute at any Season; or for any other Latitudes whatsoever.