Means of preserving the Health of Soldiers, the follow ing easy method of keeping water clear and sweet, ascertained by several experiments, made some years ago by the Society for the Encouragement of Arts, &c., in London. The method is to mix clay with the water in such quantities, that when the clay is dissolved, the hand immersed under the surface of the water shall not be seen. The clay subsiding, carries down with it all the impurities, and, in a manner burying them, prevents their communicating any bad taste or smell to the water, which thereby continues long clear and sweet. Clay may probably correct stagnant water, and thereby preserve it clear and good in dry seasons, and may thus become very useful, where there is no running water. If any bad taste or smell remains after the use of the clay, it may be carried off by one of the ventilators recommended for that purpose by the Reverend Dr. Hales. The clear water may be drawn off by a siphon or a cock, placed high enough not to touch the clay.

A. S.

TO MISS MARY STEVENSON.

Method of contracting Chimneys. - Modesty in Dis

putation.

Craven Street, Saturday Evening, past ten.

The question you ask me is a very sensible one, and I shall be glad if I can give you a satisfactory anThere are two ways of contracting a chimney; one, by contracting the opening before the fire; the other, by contracting the funnel above the fire. If the

swer.

funnel above the fire is left open in its full dimensions, and the opening before the fire is contracted; then the coals, I imagine, will burn faster, because more air is directed through the fire, and in a stronger stream; that air which before passed over it, and on each side of it, now passing through it. This is seen in narrow stove chimneys, when a sacheverell or blower is used, which still more contracts the narrow opening. But if the funnel only above the fire is contracted, then, as a less stream of air is passing up the chimney, less must pass through the fire, and consequently it should seem that the consuming of the coals would rather be checked than augmented by such contraction. And this will also be the case, when both the opening before the fire. and the funnel above the fire are contracted, provided the funnel above the fire is more contracted in proportion than the opening before the fire.

So you see I think you had the best of the argument; and, as you notwithstanding gave it up in complaisance to the company, I think you had also the best of the dispute. There are few, though convinced, that know how to give up, even an error, they have been once engaged in maintaining; there is therefore the more merit in dropping a contest where one thinks one's self right; it is at least respectful to those we converse with. And indeed all our knowledge is so imperfect, and we are from a thousand causes so perpetually subject to mistake and error, that positiveness can scarce ever become even the most knowing; and modesty in advancing any opinion, however plain and true we may suppose it, is always decent, and generally more likely to procure assent. Pope's rule,

To speak, though sure, with seeming diffidence,"

is therefore a good one; and, if I had ever seen in your

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

I am, &c.

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

* 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 in theology.-EDitor.

have enclosed to you two copies, one directed to the 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 pro

priety 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.*

TO NEVIL MASKELYNE, ASTRONOMER ROYAL.

Containing an Account of Professor Winthrop's Observation of the Transit of Mercury over the Sun, November 9th, 1769.

READ AT THE ROYAL SOCIETY, JANUARY 10th, 1771.

DEAR SIR,

Craven Street, 12 February, 1770.

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.