cure; though puzzled and fatigued, yet not caring to give it up, I recollected that I had fome metal which was reserved out of curiofity, and was a part of one of the bells of St. Andrew's which had been re-caft. Expecting, however, very little from this grois and uncertain compofition, I was nevertheless determined to fee what could be made of it by enriching the compofition with a little fresh tin. According ly cafting a metal with it, it turned out perfectly free from pores, and in every refpect as fine à metal as ever I faw.

I could not at first conceive to what this fuccefs was owing; but at last I hit upon the real caufe of that defect, which had given me fo much embarraffment and trouble during a course of near a hundred experiments, and in confequence thereof fell upon a method which ever after prevented it.

I had hitherto always melted the copper. first, and when it was fufficiently fufed, I used to add the proportional quantity of tin; and as foon as the two were mixed, and the fcoria taken off, the metal was poured into the moulds. I began to confider that putty was calcined tin, and ftrongly fufpected, that the exceffive heat which the copper neceffarily undergoes before fufion, was fufficient to reduce part of the tin to this ftate of calcination, which therefore might fly off from the compofition in the form of putty, at the time the metal was poured into the flasks.

Upon this idea, after I had furnished myself with fome more Swedish copper and grain-tin (both which I had always before used) I melted the copper, and having

added the tin as ufual to it, caft the whole into an ingot: this was, as I expected, porous. I then, melted it again, and as in this mixed ftate it did not acquire half the heat which was before neceffary to melt the copper alone, so it was not fufficient to calcine the tin; the fpeculum was then perfectly close, and free from this fault; nor did I ever after, in a fingle inftance, meet with the above-mentioned imperfection.

All that is neceffary, therefore,. to be done to procure a metal which fhall be white, as hard as it can be wrought, and perfectly compact, is to melt two pounds of Swedish copper, and when fo melted, to add fourteen ounces and a half of graintin to it; then, having taken off the fcoria, to caft it into an ingot. This metal must be a fecond time melted to caft the fpeculum; but as it will fufe in this compound state with a small heat, and therefore will not calcine the tin into putty, it fhould be poured off as foon as it is melted, giving it no more heat than is abfolutely neceffary. It is to be observed, however, that the fame metal, by frequent melting, lofes fomething of its hardness and whiteness: when this is the cafe, it becomes neceffary to enrich the metal by the addition of a little tin, perhaps in the proportion of half an ounce to a pound. And indeed when the metal is first made, if instead of adding the fourteen ounces and a half of tin to the two pounds of melted copper, about one ounce of the tin were to be referved and added to it in the fucceeding melting, before it is caft off into the moulds, the compofition would be the more beau

14

-tiful

make the heap fix or seven feet in thickness, covering it over with old mats, or any thing else, to prevent the upper leaves from being blown away. In a few days the heap will come to a ftrong heat. For the first year or two that I used thefe leaves, I did not continue them in the heat longer than ten days or a fortnight; but in this I discovered a confiderable inconvenience, as they fettled fo much when got into the hot-houfe as foon to require a fupply. Taught by experience, I now let them remain in the heap for five or fix weeks, by which time they are properly prepared for the hothoufes. In getting them into the pine-pits, if they appear dry, we water them again, trading them in layers exceedingly well till the pits are quite full. We then cover the whole with tan to the thickness of two inches, and tread it well till the furface become fmooth and even. On this we place the pinepots in the manner they are to ftand, beginning with the middle row first, and filling up the fpaces between the pots with tan. like manner we proceed to the next row till the whole be finished; and this operation is performed in the fame manner as when tan only is ufed.

In

After this the leaves require no farther trouble the whole feason through, as they will retain a conftant and regular heat for twelve months without either ftirring or turning; and if I may form a judgment from their appearance when taken out, (being always entire and perfect) it is probable they would continue their heat through a fecond year; but as an annual fupply of leaves is easily obtained,

fuch a trial is hardly worth the trouble of making.

After this the pines will have no occafion to be moved but at the ftated times of their management, viz. at the fhifting them in their pots, &c. when at each tine a little fresh tan fhould be added to make up the deficiency arifing from the fettling of the beds; but this will be inconfiderable, as the leaves do not fettle much after their long couching. During the two first years of my practice I did not ufe any tan, but plunged the pinepots into the leaves, and just covered the furface of the beds, when finished, with a little faw-duft, to give it a neatness. This method was attended with one inconvenience; for by the caking of the leaves they fhrunk from the fides of the pots, whereby they became exposed to the air, and at the fame time the heat of the beds was permitted to escape.

Many powerful reafons may be given why oak leaves (for I have not tried any other kinds) are preferable to tanners bark.

Firft, They always heat regularly; for during the whole time that I have ufed them, which is near seven years, I never once knew of their heating with violence; and this is fo frequently the cafe with tan, that I affirm, and indeed it is well known to every person converfant in the management of the hot-houfe, that pines fuffer more from this one circumftance, than from all the other accidents put together, infects excepted. When this accident happens near the time of their fruiting, the effect is foon feen in the fruit, which always comes ill fhaped and exceedingly fmall. Sometimes there will

be

be little or no fruit at all; therefore gardeners who make ufe of tan only for their pines, fhould be most particularly careful to avoid an over-heat at that critical feafon-the time of herwing fruit.

Secondly, The heat of oak leaves is conftant; whereas tanners bark generally turns cold in a very short time after its furious heat is gone off. This obliges the gardener to give the tan frequent turnings in order to promote its heating. Thele frequent turnings (not to mention the expence) are attended with the wort confequences; for by the continual moving of the pots backwards and forwards, the pines are expofed to the extremes of heat and cold, whereby their growth is conderably retarded; whereas when leaves are used, the pines will have no occafion to be moved but at the times of potting, &c. The pines Irave one particular advantage in this undisturbed fituation; their roots grow through the bottoms of the pots and mat amongst the leaves in a furprizing manner. From the vigour of the plants, when in this fituation, it is highly probable that the leaves, even in this ftate, afford them an uncommon and agree. able nourishment.

Thirdly, There is a faving in point of expence, which is no inconfiderable object in places where tan cannot be had but from a great diftance, as is the cafe here, the article of carriage amounting to ten hillings for each waggon-load. Indeed, this was the principal reafon that first induced me to make trial of leaves.

My laft ground of preference, is the confideration that decayed

leaves make good manure; whereas rotten tan is experimentally found to be of no value. I have often tried it both on fand and clay, also on wet and dry lands, and never could difcover, in any of my experiments, that it deferved the name of a manure; whereas decayed leaves are the richest, and of all others, the moft fuitable for a garden. But this mult only be underfood of leaves after they have undergone their fermentation, which reduces them to a true vegetable mould, in which we experimentally know that the food of plants is contained-but whether that food be oil, mucilage, or falt, or a combination of all three, I leave to philofophers to determine. This black moulds, of all others, the molt proper to mix with compost earth, and I use it in general for pines, and almoft for every thing that grows in pots. For flowers it is not excellent. The remainder of this vegetable mould may be employed in manuring the quarters of the kitchen-garden, for which purpofe it is highly ufeful.

Leaves mixed with dung make excellent hot-beds-and I find that beds compounded in this manner preferve their heat much longer than when made entirely with dung. In both cafes the application of leaves will be a confiderable faving of dung, a circumftance very agreeable, as it will be the means of preventing the contefts frequently obferved in large families, between the fuperintendant of the gardens and the directors of the hufbandry. Welbeck, Feb. 20, 1776.

W. SPEECHLY.

Ufeful

Useful Hints for learning to Swim. By Benjamin Franklin, LL.D. F. R. S. In a Letter to a Friend.

Dear Sir,

I CANNOT be of opinion with

CANNOT be of opinion with

for you to learn to fwim; the river near the bottom of your garden, affords a moft convenient place for the purpose. And, as your new employment requires your being often on the water, of which you have fuch a dread, I think you would do well to make the trial; nothing being fo likely to remove thofe apprehenfions, as the consciousness of an ability to fwim to the fhore in cafe of an accident, or of fupporting yourself in the water till a boat could come to take you

up.

I do not know how far corks or bladders may be useful in learning to fwim, having never feen much trial of them. Poffibly they may be of fervice in fupporting the body while you are learning what is called the stroke, or that manner of drawing in and ftriking out the hands and feet that is neceffary to produce progreffive motion. But you will be no fwimmer till you can place fome confidence in the power of the water to fupport you; I would therefore advife the acquiring that confidence in the first place, efpecially as I have known feveral who, by a little of the practice neceffary for that purpofe, have infenfibly acquired the ftroke, taught as it were by na

ture.

The practice I mean is this: chufing a place where the water deepens gradually, walk coolly into it till it is up to your breaft, then turn round your face to the

fhore, and throw an egg into the water, between you and the shore; it will fink to the bottom, and be eafily feen there, as your water is clear. It muit lie in the water fo deep, as that you cannot reach it to take it up but by diving for it. To encourage yourself in order to do this, reflect that your progrefs will be from deeper to fhallower water, and that at any time you may, by bringing your legs under you, and ftanding on the bottom, raife your head far above the water.

Then plunge under it with your eyes open, throwing yourself towards the egg, ad endeavouring, by the action of your hands and feet against the water, to get forward till within reach of it. In this attempt you will find that the water buoys you up against your inclination; that it is not fo easy a thing to fink as you imagined; that you cannot, but by active force, get down to the egg. Thus you feel the power of the water to fupport you, and learn to confide in that power; while your endeavours to overcome it, and to reach the egg, teach you the manner of acting on the water with your feet and hands, which action is afterwards ufed in fwimming to fupport your head higher above water, or go forward through it.

to

I would the more earnestly prefs you to the trial of this method, because, though I think I fatisfied you that your body is lighter than water, and that you might float in it a long time with your mouth free for breathing, if you would put yourself in a proper potture, and would be ftill, and forbear ftruggling, yet, till you have ob. tained this experimental confidence in the water, I cannot depend on

your