under side, whence it strikes into the earth, or to their farther end, whence it strikes into neighboring clouds; so that when the great cloud has passed or removed farther, they are left in a negative state, like the apparatus; they being, as well as it, often insulated bodies, not in contact with the earth or one another. And in the same manner it is equally easy to conceive how a large negative cloud may make others positive. The experiment you mention of filing the glass is similar to one I made in 1751, or 1752. I had supposed in my letter that the internal pores of glass were less than those near the surface, and so denied a passage to the electric fluid. To try whether this was so in fact, I ground one of my phials on one side extremely thin, passing a good way beyond the middle of the thickness, and very near to the other side, as I found on breaking it after the experiment. It charged as well after grinding as before; which satisfied me that my hypothesis was in that particular wrong. It is hard to conceive where the additional quantity on the charged side of glass is deposited, there is so much of it. I send you my meteorological paper, which has lately been printed here in the Transactions, following a paper of Mr. Hamilton's on the same subject. I am, &c. B. FRANKLIN.

CONJECTURE AS TO ELEPHANTS BEING NATIVES OF

AMERICA.

To MR. Croghan.

SIR,

London, Aug. 5, 1767.

I return you many thanks for the box of elephants' tusks and grinders. They are extremely curious on many accounts; no living elephants having been seen in any part of America by any of the Europeans settled there, or remembered in any tradition of the Indians. It is also puzzling to conceive what should have brought so many of them to die on the same spot; and that no such remains should be found in any other part of the continent, except in that very distant country Peru, from whence some grinders of the same kind formerly brought, are now in the museum of the Royal Society. The tusks agree with those of the African and Asiatic elephant, in being nearly of the same form and texture; and some of them, notwithstanding the length of time they must have lain, being still good ivory. But the grinders differ, being full of knobs, like the

grinders of a carnivorous animal; when those of the elephant, who eats only vegetables, are almost smooth. But then we know of no other animal with tusks like an elephant to whom such grinders might belong. It is remarkable, that elephants now inhabit naturally only hot countries where there is no winter, and yet these remains are found in a winter country; and it is no uncommon thing to find elephants' tusks in Siberia, in great quantities, when their rivers overflow, and wash away the earth, though Siberia is still more a wintery country than that on the Ohio; which looks as if the earth had anciently been in another position, and the climates differently placed from what they are at present. With great regard, I am, sir, your most obedient humble servant,

B. FRANKLIN.

ON THE COLICA PICTORUM, AND PERNICIOUS USE OF LEAD IN DISTILLERIES.

DEAR SIR,

TO DR. EVANS.

London, February 20, 1768.

I wrote you a few lines by Capt. Falconer, and sent you Dr. Watson's new piece of Experiments in Inoculation, which I hope will be agreeable to you. In yours of Nov. 20, you mention the lead in the worms of stills as a probable cause of the dry belly-ache among punch-drinkers in our West Indies. I had before acquainted Dr. Baker with a fact of that kind, the general mischief done by the use of leaden worms, when rum-distilling was first practised in New England, which occasioned a severe law there against them; and he has mentioned it in the second part of his piece not yet published. I have long been of opinion, that that distemper proceeds always from a metallic cause only; observing that it affects, among tradesmen, those that use lead, however different their trades-as glaziers, letter-founders, plumbers, potters, white-lead makers, and painters: from the latter, it has been conjectured, it took its name colica pictorum, by the mistake of a letter, and not from its being the disease of Poictou; and although the worms of stills ought to be of pure tin, they are often made of pewter, which has a great mixture in it of lead.

The Boston people pretending to interfere with the manufactures of this country, make a great clamor here against America in general. I have therefore endeavored to palliate matters a little in several public papers. It

would, as you justly observe, give less umbrage if we meddled only with such manufactures as England does not attend to. That of linen might be carried on more or less in every family, and silk, I think, in most of the colonies. But there are many manufactures that we cannot carry on to advantage, though we were at entire liberty. And after all, the true source of riches is husbandry. That is truly productive of new wealth; manufacturers only change forms, and whatever value they give to the materials they work upon, they at the same time consume an equal value in provisions, &c. So that riches are not increased by manufacturing; the only advantage is, that provisions in the shape of manufactures are more easily carried for sale to foreign markets. And where they cannot be easily carried to market, 'tis well so to transform them for our own use as well as foreign sale. In families also, where the children and servants of families have some spare time, 'tis well to employ it in making something. I am, with thanks for your good wishes, dear sir, yours, &c. B. FRANKLIN.

ON CHIMNIES, &c.

TO LORD KAIMES.

London, Feb. 28, 1768.

IT gave me great pleasure to see my dear good friend's name at the foot of a letter I received the other day, having been often uneasy at his long silence, blaming myself as the cause by my own previous backwardness and want of punctuality as a correspondent. I now suppose, (as in this he mentions nothing of it,) that a long letter I wrote him about this time twelvemonth, on the subject of the disputes with America, did miscarry, or that his answer to that letter miscarried, as I have never heard from him since I wrote that letter.

I have long been of an opinion similar to that you express, and think happiness consists more in small conveniencies or pleasures that occur every day, than in great pieces of good fortune that happen but seldom to a man in the course of his life. Thus I reckon it among my felicities, that I can set my own razor, and shave myself perfectly well; in which I have a daily pleasure, and avoid the uneasiness one is sometimes obliged to suffer from the dirty fingers or bad breath of a slovenly barber.

I congratulate you on the purchase of a new house so much to your mind, and wish that you may long inhabit it with comfort. The inconvenience you mention of neighboring smoke coming down the vents, is not owing to any bad construction of the vent down which it comes, and therefore not to be remedied by any change of form. It is merely the effect of a law of nature, whereby, whenever the outward air is warmer than the walls of the vent, the air included being by those walls made colder, and of course denser and heavier than an equal column of the outward air, descends into the room, and in descending draws other air into the vent above to supply its place; which being in its turn cooled and condensed by the cooler walls of the vent descends also, and so a current downwards is continued during the continuance of such difference in temperament between the outward air and the walls of the vent. When this difference is destroyed, by the outward air growing cooler, and the walls growing warmer, the current downwards ceases; and when the outward air becomes still colder than the walls, the current changes and moves from below upwards, the warmer walls rarefying the air they include, and thereby making it so much lighter than a column of the outward air of equal height, that it is obliged to give way to the other's superior weight and rise, is succeeded by colder air, which being warmed and rarefied in its turn, rises also, and so the upward current is continued. In summer, when fires are not made in the chimnies, the current generally sets downward from nine or ten in the morning during all the heat of the day, till five or six in the afternoon, then begins to hesitate, and afterwards to set upwards during the night, continuing till about nine in the morning, then hesitating for some time before it again sets downwards for the day. This is the general course, with some occasional variation of hours, according to the length of days or changes of weather. Now when the air of any vent is in this descending state, if the smoke issuing from a neighboring vent happens to be carried over it by the wind, part will be drawn in and brought down into the room. The proper remedy then is, to close the opening of the chimney in the room by a board so fitted that little or no air can pass, whereby the currents above-mentioned will be prevented. This board to remain during the summer, and when fires are not made in the chimney. Chimnies that have fires in them daily are not subject to this inconvenience, the walls of their vents being kept too warm to occasion any downward current during the hours between the going out of one fire and the kindling of another. And indeed, in summer, those vents that happen to go up close joined with the 3 A

VOL. III.

kitchen vent, are generally kept so warm by that as to be free from the downward current, and therefore free from what you call neighbor smoke.

The Philadelphia grate which you mention is a very good thing, if you could get one that is rightly made, and a workman skilful in putting them up. Those generally made and used here are much hurt by fancied improvements in their construction, and I cannot recommend them. As fuel with you is cheap and plenty, a saving in it is scarce an object. The sliding plates (of which I sent a model to Sir Alex. Dick) are in my opinion the most convenient for your purpose, as they keep a room sufficiently warm, are simple machines, easily fixed, and their management easily conceived and understood by servants.

Lshall leave Europe with much greater regret if I cannot first visit you and my other friends in Scotland. I promise myself this happiness, but am not yet clear that I shall have time for it. Your kind invitation is extremely obliging. With sincere esteem I am, my dear friend, your's most affectionately,

B. F.

ON ASTRONOMICAL SUBJECTS, ELECTRICITY, &c.

TO MR. WINTHORP.

DEAR SIR, London, July 2, 1768. You must needs think the time long that your instruments have been in hand. Sundry circumstances have occasioned the delay. Mr. Short, who undertook to make the telescope, was long in a bad state of health, and much in the country for the benefit of the air. He however at length finished the material parts that required his own hand, and waited only for something about the mounting that was to have been done by another workman; when he was removed by death. I have put in my claim to the instrument, and shall obtain it from the executors as soon as his affairs can be settled. It is now become much more valuable than it would have been if he had lived, as he excelled all others in that branch. The price agreed for was 1001.

The equal altitudes and transit instrument was undertaken by Mr. Bird, who doing all his work with his own hands for the sake of greater truth and exactness, one must have patience that expects any thing from him. He is so singularly eminent in his way, that the commissioners of longitude have lately given him 5001. merely to discover and make public his method of dividing