vember, the magazine was filled with water, as high as it was cut out of the rock. When drains were made to carry off the water, the magazine then became, and continued to be sufficiently dry.

Might not low grounds on the banks of rivers, similar to those in Flanders, and so justly and judiciously complained of by Sir John Pringle, be rendered more healthy, by drains dug as deep as low-water mark in the adjacent rivers? Sluices might be made in the banks of the river, to prevent the tides or floods from entering into the drains. It would be advisable to cover the drains, to prevent the noxious vapors arising from putrid animal or vegetable substances, which generally rot in open ditches. The earth thrown out of the drains might serve to cover them, when the channels for carrying off the water are properly constructed. By these means no surface would be lost for the growth of vegetables.

Willows, alders, and such trees as delight in a moist or wet soil, may be planted on the banks of ditches, if any such are permitted to remain open, that their leaves may correct the putrid vapors arising from the stagnant water in the ditches. I fear, however, that in the autumn, when the effects of putrid vapors are most severely felt, the leaves of these trees, being then hardened by age, may in a great measure lose the power of correcting the putrid vapors. The late summer shoots may afford aid till the equinoxial rains clear the ditches of all filth. That trees have not the power of proving an effectual remedy against these putrid exhalations, the frequency of agues in the low countries,

in

every such season, is a sufficient proof. If such trees grow on the banks of ditches, they should be kept in a pollard state, to admit of a free circulation of air.

An observation of Dr. Franklin's deserves a place

here, especially as it is not generally attended to. The opinion is indeed against it. The banks of rivers which have a quick motion, and run on a clear sandy bottom, are very agreeable and healthy situations; but the sides of rivers which have oozy bottoms, or marshy banks, or which are in the neighbourhood of extensive marshes, are to be avoided. When necessity or any peculiar advantage obliges people to build near such bad neighbours, the south side, says the Doctor, is the most eligible; because the warm southerly winds, which promote a tendency to putrefaction, and are the most frequent, blow the noxious vapors from the buildings; whereas the northerly winds, which blow but seldom compared with the former, and which generally blow strongly, check putrefaction, and speedily carry off noxious vapors.

It is now well known that the stench arising from stationary privies, may be prevented by a cheap and easy method. The excrements may be received in tubs, so closely connected with the seat, that no air can pass. The lower ends of the tub should be sunk below the surface of water contained in proper cisterns. The excrements are soon dissolved in water, and so carried off, every time the privy is washed, which should be as often as it is used.

In towns the stench of the common sewers is sometimes very offensive. This may be prevented by interrupting the current of air through them by means of stink-traps; the construction and utility of which, are of late years well known in London. As sand or other filth may be apt to lodge in the deepened place, it should be so contrived, as to be easily come at, in order to clear away every obstruction.

Let me add here to the method of correcting bad water, proposed by Dr. Munro, in his Essay on the

Means of preserving the Health of Soldiers, the following 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.

TO MISS MARY STEVENSON.

A. S.

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 answer. There 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

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

VOL. VI.

BB

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

I am, &c.

B. FRANKLIN.

FROM JOHN EWING TO B. FRANKLIN.*

Transmitting Observations of the Transits of Venus and Mercury. - Proposal for an Observatory in Philadelphia.

SIR,

Philadelphia, 4 January, 1770.

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.