account for.”—The Facts are so, and this public Relation of them is extorted from me, by a Conviction that no other Way is left me to obtain Justice, or so likely to prevent the Invention from perishing. However, if it is expected of me, like Mr. Maskelyne, to deliver an Opinion on this Point, I shall declare what I believe very sincerely, that by far the greater Part of the Commissioners are perfectly innocent of the Treatment I have met with: most of them are Commissioners by Virtue of great Employments which engage their Time and Attention: A Board so constituted is continually changing; and this being a Matter of Science which to many may seem rather abstruse, it was very naturally left to the Management of a few of those Members who stand in the most immediate Relation to Science, and whose Opinions, upon a Business of this Nature, the rest of the Board had too much Modesty to call in Question. How well they have merited that Degree of Confidence is left to the impartial World to determine.

To return again to Mr. Maskelyne’s Account: He, as I think has been already shewn, having said and done every Thing in his Power to the Dishonour and Discouragement of my Invention, scruples not to sum up his Opinion of it in the following Terms:

“That Mr. Harrison’s Watch cannot be depended upon to keep the Longitude within a Degree, in a West-India Voyage of six Weeks, nor to keep the Longitude within Half a Degree for more than a Fortnight, and then it must be kept in a Place where the Thermometer is always some Degrees above freezing: that, in case the Cold amounts to freezing, the Watch cannot be depended upon to keep the Longitude within Half a Degree for more than a few Days, and perhaps not so long, if the Cold be very intense: nevertheless, that it is a useful and valuable Invention, and in Conjunction with the Observations of the Distance of the Moon from the Sun and fixed Stars, may be of considerable Advantage to Navigation.”

Having sufficiently refuted the first Part of this Opinion already, it only remains for me to make such Remarks on the Lunar Method of finding the Longitude, as this coupling of my Invention with it seems to call upon me for.

It is with Reluctance that I follow Mr. Maskelyne into a Subject in which I may seem, like him, to be actuated by a selfish Preference to my own Scheme; however, as I shall give my Reasons for what I advance, I will not hesitate to submit them to the Public. I beg to be understood as a warm and declared Friend to that and every other Mode which can be devised of ascertaining the Longitude at Sea, so long as they keep within the Bounds of Reason and Probability. Here are now two Methods before the Public; Wou’d to God there were two Hundred! The Importance of the Object would warrant public Encouragement to them all; but, called upon to say something on the Subject, I think it incumbent upon me to point out those Limits beyond which its Utility cannot, from the Nature of the Thing, be extended.

The Method of finding the Longitude by the Moon, in which Mr. Maskelyne is in a pecuniary way interested, is this.—If the apparent Distance between the Sun and Moon, or between the Moon and some fix’d Star, at any certain Part of the Globe, was for every Hour of the Year known; and if a Navigator, when at Sea, could also, by Observations, ascertain what is the apparent Distance, at the Place where he is, between the Sun and Moon, or between the Moon and a Star, and likewise their respective Altitudes; and if he could also, at the same Moment, ascertain the Time of the Day, either by an immediate Observation of the Sun, or by a Watch which would keep Time pretty exactly from the last solar Observation; these Matters of Fact being given, the Difference of Longitude may from thence be calculated. I admit the Principle to be absolutely true in Theory. The Lunar Tables, for which the Rewards have been given, are calculated to shew the Distance between the Sun and Moon, or Moon and Stars, at Greenwich; I admit the Practicability of making such Tables; but with Regard to the other Requisites, I beg Leave to observe that, for six Days in every Month, the Moon is too near the Sun for observing, consequently, during those Days, the Method falls totally to the Ground; that for about other thirteen Days in every Month, the Sun and Moon are at too great a Distance for observing them at the same Time, or are not at the same Time visible; therefore, during those 13 Days, we must depend upon Observations of the Moon and Stars, and upon a Watch to keep Time, from the last Solar Observation with sufficient Exactness, which common Watches cannot be depended upon to do; well therefore might Mr. Maskelyne admit that my Invention would become of considerable Value, even if taken in Aid of the Lunar Tables. I leave the Reader to judge of the Practicability of making these Observations from what follows:

To ascertain the Longitude by the Moon and a Star, requires a distinct Horizon to be seen in the Night, which is next to impossible, and if you have not an Horizon, the Altitude of neither Moon nor Star can be taken: It also requires (and this perhaps when a Ship is in a high Sea) the Distance of the Moon and Star, in order to come at which, the Image of one of them must be reflected through a silvered Glass, and the other seen through an unsilvered Part of the same Glass; and they must be brought into Conjunction in the Line that connects the silvered and unsilvered Parts, and this to an Exactness only true in Theory, for an Error of a Minute of a Degree committed in this Observation, will mislead the Mariner Half a Degree in his Longitude; Now I call upon any Astronomers of Reputation publickly to declare, that they have, even at Land, and with the best Instruments Europe affords, been able to make this Observation of the Moon and a Star with any thing like the Precision required to determine the Longitude within the Limits required by the Act of the 12th of Queen Anne; I know it cannot be done. Nay I further call upon any such Astronomers to declare, whether even in Observations of the Distance between the Sun and Moon, two of them observing together have generally speaking agreed in this Observation within a Minute of a Degree: I know that in general the Difference between the best Observers even at Land will be more, and as a farther Proof of this Assertion, I refer the Reader to the Note below:[6] And if these Matters of Fact are still doubted, I shall beg Leave to call upon Mr. Maskelyne and Mr. Green to declare how near they, with Admiral Tyrrel agreed in determining the Longitude by the Sun and Moon in their Voyage to Barbadoes; and also whether during that Voyage they ever did determine their Longitude by the Moon and Stars.—I know they did not, for they found the Observation too difficult, and indeed it is only true in Theory.

From the foregoing Premises I infer,

1st. That during six Days in every Month, no Observations can be made by this Method to ascertain the Longitude at Sea.

2dly, That during 13 other Days in each Month, it is impracticable to ascertain it by this Method with any Instruments hitherto contrived, or which the Nature of the Service to be performed seems to admit of

And 3dly, That during the remaining 11 Days in each Month, when the Sun and Moon may, if the Weather is clear be observed at the same Time, no Reliance can safely be placed upon the