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conversation the least deviation from it, I should earnestly recommend it to your observation.

I am, &c.



Transmitting Observations of the Transits of Venus

and Mercury. Proposal for an Observatory in Philadelphia.

Philadelphia, 4 January, 1770. SIR, Our Philosophical Society have at length ordered me to draw out an account of our observations of the transits of Venus and Mercury, to be transmitted to you as our President, through whose hands we think they may be most conveniently communicated to the learned societies of Europe, to whom you may suppose they will be agreeable. The reason of their not coming sooner to hand was a rash agreement of the Society not to send them abroad, until we had printed them in our own Transactions. But finding that there was some reason to suspect, that partial accounts of them had been transmitted to England by some of our members privately, which possibly might be inaccurate and not much to be depended on, the Society have thought proper to reconsider that hasty agreement, and to send them without farther loss of time. We hope, however, that they will be as soon with you, as those that have been made in South America and the East Indies. I · have enclosed to you two copies, one directed to the

* Dr. Ewing was a clergyman of Philadelphia, and for many years Provost of the University of Pennsylvania. He was a scholar of large attainments in various branches of science and literature, as well as 10 theology.- EDITOR

Astronomer Royal, Mr. Maskelyne, at Greenwich, and the other to be transmitted by you to any of the learned societies in Europe you shall think proper.

You are well acquainted with the serenity of our air, and the advantages we enjoy above many countries in Europe for making celestial observations, could a fixed observatory be established in Philadelphia. I have mentioned this matter to Mr. Maskelyne, and referred him to you for advice how to bring it into execution, should it meet with your approbation. You are well acquainted with the views of our Assembly, and the unreasonableness of expecting that they would lay out any of the public money for such a purpose, unless it was recommended by you to them; as they place an unreserved confidence in your judgment concerning what measures would tend to the reputation of the province, the advancement of useful knowledge, and the benefit of the public in general. Geography, navigation, and the arts that depend upon them, are daily reaping advantages from the astronomical observations made in the different observatories of Europe. Should you think it of any consequence, that we in this infant country might bear any part in these things, your known character and ability to judge in these matters must necessarily have so much influence with our Assembly, as to induce them to bear at least a part in the expense of it. And possibly Mr. Maskelyne might suggest some means of affording assistance from home, from the consideration of its being made subservient to his observatory at Greenwich, and put under his general direction.

I have not mentioned this proposal to any person here, but Mr. Coombe, and that under a promise that he will not speak of it, as I apprehend there is a propriety in its coming from you and the Astronomer Royal. So that if it does not meet with your approbation, pray let it sleep, and be so kind as to excuse the trouble given you by, Sir, your most obedient servant,

John Ewing.

P.S. Mr. Coombe tells me, that he has mentioned the above proposal to his son, with a desire that he should speak to you on the subject.

Please send me authentic accounts of the observations of the transit of Venus made in as many places as you can conveniently procure, if your leisure from more important business will permit, that we may here also endeavour to solve the curious problem of the sun's parallax. If it would not be trespassing too much, I should also be much obliged to you for an account of Messrs. Mason's and Dixon's determinations on the length of a degree of latitude here, as they have been employed by the Royal Society to measure it in the Lower Counties.*


Containing an Account of Professor Winthrop's 06

servalion of the Transit of Mercury over the Sun, November 9th, 1769.


Craven Street, 12 February, 1770. DEAR SIR, I have just received a letter from Mr. Winthrop, dated December 7th, containing the following account, viz.

A brief and interesting account of the observations, in America, of the transits of Venus and Mercury, including those mentioned above, may be found in Professor Renwick's Life of RITTENHOUSE, contained in the seventh volume of the Library of American Biography. — EDITOR.

“On Thursday, the 9th of November, I had an opportunity of observing a transit of Mercury. I had carefully adjusted my clock to the apparent time, by correspondent altitudes of the Sun, taken with the quadrant for several days before, and with the same reflecting telescope as I used for the transit of Venus. I first perceived the little planet making an impression on the sun's limb at 21 52'41"; and he appeared wholly within at 53' 58" apparent time. The sun set before the planet reached the middle of his course; and for a considerable time before sunset, it was so cloudy, that the planet could not be discerned. So that I made no observations of consequence, except that of the beginning, at which time the sun was perfectly clear. This transit completes three periods of forty-six years, since the first observation of Gassendi at Paris, in 1631."

I am, Sir, with great esteem,
Your most obedient servant,



Respecting covering Houses with Copper.

London, 17 March, 1770. DEAR SIR, I received your favor of November 25th, and have made inquiries, as you desired, concerning the copper covering of houses. It has been used here in a few instances only, and the practice does not seem to gain ground. The copper is about the thickness of a common playing-card; and, though a dearer metal than

* See Philosophical Transactions, Vol. LIX. p. 352. VOL. VI. 42


lead, I am told, that, as less weight serves, on account of its being so much thinner, and as slighter woodwork in the roof is sufficient to support it, the roof is not dearer on the whole, than one covered with lead.

It is said, that hail and rain make a disagreeable drumming noise on copper; but this I suppose is rather fancy; for the plates being fastened on the rafters must, in a great measure, deaden such sound. The first cost, whatever it is, will be all, as a copper covering must last for ages; and, when the house decays, the plates will still have intrinsic worth. In Russia, I am informed, many houses are covered with plates of iron tinned, such as our tin pots and other vases are made of, laid on over the edges of one another like tiles; and which, it is said, last very long, the tin preserving the iron from much decay by rusting. In France and the Low Countries, I have seen many spouts or pipes for conveying the water down from the roofs of houses, made of the same kind of tin plates soldered together ; and they seem to stand very well.

With sincere regard, I am
Yours, &c.



Philadelphia, 14 June, 1770. SIR, I received your very agreeable letter, in which you acknowledge the receipt of our observations of the transit of Venus. I herewith send you a few copies of them, as they are printed in our Transactions, and I suppose in a more perfect form than that in which they were sent before, as that was done in a hurry, and I

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