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Know, is immense. In this engine, it is made to exert itself to wards the working of pumps. That of Paris, is, I believe, the largest known, raising four hundred thousand cubic feet (French) of water, in twenty-four hours : or rather, I should have said, those of Paris, for there are two under one roof, each raising that quantity.
The Abbs Rochon not living at Paris, I have not had an op portunity of seeing him, and of asking him the questions you desire, relative to the crystal of which I wrote you. I shall avail myself of the earliest opportunity I can, of doing it. I shall cheer fully execute your commands as to the Encyclopedic, when I receive them. The price will be only thirty guineas. About half the work is out. The volumes of your Buffon which are spoiled, can be replaced here.
I expect that this letter will be carried by the Mr. Fitzhughs, in a ship from Havre to Portsmouth. I have therefore sent to Havre, some books which I expected would be acceptable to you. These are the Bibliotheque Physico-oeconomique, which will give you most of the late improvements in the arts; the Connoissance des terns for 1786 and 1787, which is as late as they are published ; and some pieces on air and fire, wherein you will find all the discoveries hitherto made on these subjects. These books are made into a packet, with your address on them, and are put into a trunk wherein is a small packet for Mr. Wythe, another for Mr. Page, and a parcel of books, without direction, for Peter Carr. I have taken the liberty of directing the trunk to you, as the surest means of its getting safe. I pay the freight of it here, so that there will be no new demands, but for the transportation from the ship s side to Williamsburg, which I will pray you to pay; and as much the greatest part is for my nephew, I will take care to repay it to you.
In the last volume of the Connoissance des terns, you will find the tables for the planet Herschel. It is a curious circumstance, that this planet was seen thirty years ago by Mayer, and supposed by him to be a fixed star. He accordingly determined a place for it, in his catalogue of the zodiacal stars, making it the 964th of that catalogue. Bode, of Berlin, observed in 1781, that this star was missing. Subsequent calculations of the motion of the planet Herschel, shew that it must have been, at the time of Mayer s observation, where he had placed his 964th star.
Herschel has pushed his discoveries of double stars, now, to upwards of nine hundred, being twice the number of those com municated in the Philosophical Transactions. You have probably seen, that a Mr. Pigott had discovered periodical variations of light in the star Algol. He has observed the same in the *? of Antinous, and makes the period of variation seven days, four hours, and VOL. i. 42
