MEMORANDUM.
1. All Departures must be reckon’d from London, if the Movement was there Set going.
2. That wheresoever they are Set going, there must be a large and exact Meridian Line prepared by a Perpendicular, set up in an Horizontal Circle, as is Mathematically taught, &c.
3. That an Equal time be spent in Winding it up, as near as possible; for which no time need be allowed, if Equated for 10 or 12 Months; because the time required will be the same for the same time, and greater for a greater, &c.
4. That the said Movement be carefully kept in one and the same Temperature of Air, as near as possible.
5. That after this Movement is fully proved, if it should not (by reason of any sudden change of Air) agree to a Minute, yet it ought not in this respect to be altered or much regarded, because the moistness of one Month, may compensate the Dryness of another: So that by such time as you are arrived to the end of your Voyage, the Movement may even Rectifie or Correct it self.
6. It is to be noted, That if the Sun comes too soon to the Meridian, it will also come too soon to the Horizon; and therefore, Watch too fast, or too slow, must be Added or Substracted, as aforesaid.
7. That it be always wound up, as near as may be, at one certain time of the Day, (viz.) if at Sea, about Twylight, or Break of Day, as may be thought expedient. And if it should happen to be omitted, so long as to stand still; you must not set it going again, but by taking it assunder, and putting the two Indexes together, and bringing the Movement to the Meridian Line, as at first directed. Therefore when at Sea be careful of such Omissions.
8. It is to be noted, That altho’ every Minute of Time, does Answer to about 15 or 16 Miles English, under the Equinoctial; yet it is not above 9 or 10 Miles in our Latitude to one such Minute. And altho’ it be so many under the Equinoctial, yet there the Sun’s Altitude will be taken very exact, because 90 degrees of Altitude, is for 6 hours of Time; whereas in our Latitude, it is but 62 degrees, for 8 hours of Time; both which Advantages will Facilitate the Practice. I shall at present conclude with acquanting,
That if a common Minute Watch (by Filing or Loading the Ballance, or otherwise) be made to go, or does already go, any unknown quantity of Time, either too Fast, or too Slow; by this Device, we may find the Hour and Minute of the Day by such a Watch, more exactly than can be done by the best timed common Watch whatever. And this even without touching it, other than by Winding up the Spring as usual.
There are other Improvements that may be made of this Discovery, but I reserve them to some other Opportunity.
The Form of the Book to be kept for each Movement, wherein must be entred the Numbers, &c. (which are to be found at the Returning of the Ship) for finding the Hour and Minute at London.
| The Movement, Number 1. was first Set Going Sept. 4. 1714. and Then made one Revolution, in 5 days, 4 hours, and a quarter. | |||||||
|---|---|---|---|---|---|---|---|
| Degrees of Latitude. | Numbers to be found and used in finding the Hour at London. | Hours spent in producing the said Numbers. | Difference in Numbers. | Seasons in which the Ship was Sailing. | Time when the Movement was set in Motion & Try’d; at & after first Making or Cleaning. | Numbers, shewing how the Motion is retarded by Foulness, on a Tryal of 10 Days at a time. | |
| I. | II. | III. | IV. | V. | VI. | VII. | Days. |
| 50 | 29276.2 | 240 | Autumn | Sep. 16. 1714 | 29276.2 | 10 | |
| 52 | 37962.4 | 432 | Winter | Dec. 4. 1714 | 29272.5 | 10 | |
| 44 | 37942. | 430 | Spring | Ma. 20. 1715 | 29264. | 10 | |
| 48 | 37912.2 | 431 | Summer | June 1. 1715 | 29237.4 | 10 | |
| Cleansed Sept. 5. 1715. Then made one Revol. in 5 days, 4 ho. and ⅛. | |||||||
| 50 | 29274.2 | 240 | Autumn | Sept. 5. 1715 | 29274.2 | 10 | |
| 52 | 37957.9 | 432 | Winter | Dec. 17. 1715 | 29268. | 10 | |
| 44 | 37942. | 430 | Spring | Ma. 16. 1715 | 29264. | 10 | |
| 48 | 37907.5 | 431 | Summer | June 8. 1716 | 29232.7 | 10 | |
Note, That the Numbers to be used after Cleaning, (viz. after Sept. 5. 1715.) are found by Substracting or Adding the Difference between the two Numbers in the Seventh Column, (viz. that of Sept. 5.) and that of Sept. 16. (which is only 2.) out of the former Numbers to be used for the same Latitude; on which there will remain 29274.2 for the New Number to be used in Lat. 50. Deg. in Autumn, instead of the former, until the next Cleaning, (which must be only Annually) and so of the rest, from one Cleaning to another. And this method must be used for the respective Latitudes, according as Observations shall be made therein, and Numbers found to answer thereunto.
Note also, That this Experiment may be sufficiently Tryed and Proved, by only two or three Voyages, to the South-West parts of Ireland, or to Newfoundland at farthest.
But notwithstanding what has been said, It is chiefly to be noted, That altho’ I have proposed (for Example sake) that the General Numbers should be found, by Sailing to Newfoundland, Virginia, Barbados, &c. and returning again to a Meridian Line at London: Yet if the Honourable Persons before-mentioned in this Title-Page, to whom the whole is most humbly submitted, will please to appoint a Ship for this purpose, the said Numbers may be much better found in manner following; (that is to say) By ordering that the said Ship shall first make a true Meridian Line, at or near the Lat. of 60 Degrees; and thereby set the Movements going, in manner aforesaid: After which let them Sail about 40 or 50 Leagues distant from the Shore, and there Cruise Northward and Southward for about a Month’s time; after which let them return again to the same Line, and find the Numbers, and also enter them, as before directed. And having so done, let them make another Meridian Line, about 15 Deg. more Southward, and there do in like manner: And so at the like Distance to the Equinoctial. After which, let them begin again, and repeat the same Process for three or four times: By which means the Numbers will be found, and the different Motion of the Movement discover’d, for all Latitudes and Seasons, as near as needful.
And being returned home, by these Numbers we may find the true Difference of Motion, in and for the several Latitudes and Seasons. Which Difference must be entred in the 4th Column of the respective Books, reserved for that purpose. By the help of which said Differences, you may make as many Movements as may be needful, at any time; as also Books and Numbers peculiar to each Movement. The Rules for which will be imparted to any such Watchmaker, as may Reasonably desire the same.
FINIS.