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Cr the Usefulness of washing and rabbing the Stems of Trees; by Mr. Marsham.

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Had for feveral years intended to put in practice the celebrated Dr. Tolles' advice of washing, with that of Mr. Evelyn of rubbing the ftem of a tree, in order to increase its growth; but other avocations prevented me till the laft fpring: when, as foon as the buds began to fwell, I washed my tree round from the ground to the beginning of the head; viz. between thirteen and fourteen feet in height. This was done firft with water and a flif fhoe-brush, until the tree was quite cleared of the mofs and dirt: then I only washed it with a coarse flannel. I repeated the washing three, four, or five times a week, daring all the dry time of the spring, and the fore-part of the fummer; bat after the rains were frequent, I very feldom wafhed. The unwashed tree, whofe growth I propoled to compare with it, was (at five feet from the ground) before the laft year's increafe, 3 ft. 7 in

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ths; and in the autumn, after the year's growth was compleated, 3 ft. 9 in.th; viz. increase 1 in

ths. The washed tree was lat fpring 3 ft. 7 in.ths, and in the autumn it was 3 ft. 9 in. the viz. increase 2 in.ths, that as one-tenth of an inch above dostle the increase of the unwashed tree As the difference was fo great, and as fome unknown accident might. have injured the growth of the washed tree, I added the year's

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crease of five other beeches of the fame age (viz. all that I had meafured), and found the aggregate increase of the fix unwashed beeches to be 9 in.ths, which, divided by fix, gives one inch and fivetenths and an half for the growth of each tree; fo the gain by wash. ing is nine-tenths and an half. To make the experiment fairly, I fixed on two of my largest beeches, fown in 1741, and tranfplanted into a grove in 1749. The washed tree had been, from the first year, the largest plant till the year 1767, when its rival became and contiBued the largest plant, until I began to wash the other: therefore I fixed on the lefs thriving tree as the fairest trial. The trees were nearly of the fame height and hape, fpreading a circle of about fifty feet diameter. I think it neceffary to mention these circumftances; for I know by experience, that a fhort and spreading tree, having ample room, will increase twice or three times, and perhaps four times as much, as a tall fmaliheaded tree of the fame age, that ftands near other trees. Thus my washed beech increased above fix times as much as Mr. Drake's beautiful beech at Shardeloes, though that tree feemed in good health when I faw it in 1759 and 1766. Bat it increased only 2 in. ths in those seven years; which may perhaps be owing to its vaft height, being feventy-four feet and a half to the boughs (as the late knight of the fhire for Suffolk, Sir John Rous, told me that Mr. Drake had informed him) only fix feet and four inches round, and having a small head, and little room to spread.

Stratton, Oct. 29, 1775.

Directions for making the beft Com pofition for the Metals of reflecting Telefcopes, by Mr. John Mudge.

TH

HE perfection of the metal of which the fpeculum fhould be made confifts in its hardness, whitenefs, and compactness; for upon thefe properties the reflective powers and durability of the fpeculum depend. And first of the hardness and whiteness of the me. tal.

There are various compofitions recommended in Smith's Optics, all which have however their feveral defects. Three parts copper and one part and one-fourth of tin will make, he fays, a very hard white metal; but it is liable to be porous. This, however, is an imperfection which I fall prefently fhew the method of preventing; but the permanent fault of it, and which I have myfelf experienced, is, that it is not hard enough. The speculum of a reflecting telescope ought to have the utmolt poffible hardness, compatible with its being operated upon by the tool.

It is to be observed, that ever fo fmall a quantity of tin added to melted copper destroys its perfect malleability, and at the fame time produces a metal whiter and harder than copper. As the quantity of tin is increased, fuppofe to a fifth or fourth part, the metal becomes whiter, ftill harder, and confequently more friable. If the quantity of tin be further increafed to a third of the whole compofition, it will then have its utmoit whitenefs; but will be rendered at the fame time fo exceedingly hard and brittle, that the finest washed emery upon lead or brafs will not cut it without breaking up its furface; I 3

and

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cure; though puzzled and fatigued, yet not caring to give it up, I recollected that I had fome metal which was referved 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 grofs 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 respect 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 scoria taken off, the metal was poured into the moulds. I began to confider that putty was calcined tin, and strongly 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, fo 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 scoria, 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 ftate with a small heat, and therefore will not calcine the tin into putty, it should 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 firft 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

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tiful

tel, and the grain of it much be no occafion for the complicated

fer: this I know by experience to be the case.

The ber method for giving the metoa metal a good surface is this: the moment ocfore it is poured off, Crow cat de cable a spoonful t; immediately afat the metal met be stirred In a scala pitala, and poured

37

not be confidered the above detail; but tus Notes cized me a great a guze, I was willing to one event of the means by * red from this diffiouts over after. Perhaps, indeed, 12 or this procefs may be a kona v、 as many years fince, municated this compofition, eleve at the fame time the cod of preventing the pores, io Mr. Peter Collinfon, a Honoce of the Royal Society; kewe two or three years aces at the detire of my brother,

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W. Michell. Although it be duble, therefore, that this meho's generally known, yet, as I Save frequently of late feen fpecula

with this defect, and obferved metas of some of Mr. Short's telescopes which are not quite fo perred as could be wifhed (though

are a exquifitely figured) 1 wis withng by this publication wcy to remove any future emBack Flatent of this fort, and to fursa workmen with an excellent coupeation for their metals. And e Royal Society be pleafed to odour the process with a place i áca records, I know of no other co to proper to give this, as weit is the following information,

a teneral notoriety,

The metal being caft, there will

apparatus directed by Dr. Smith, for grinding and polishing it. Four tools are all that are neceffary, viz. the rough grinder to work off the rough face of the metal; a brafs convex grinder, on which the metal is to receive its spherical figure; a bed of hones, which is to perfect that figure, and to give the metal a fine fmooth face; and a concave tool or bruiser, with which both the brafs grinder, and the hones are to be formed. A polither may be confidered as an additional tool; but as the brais grinder is used for this purpcfe, and its pitchy furface is expeditioufly, and without difficulty formed by the bruifer, the apparatus is therefore not enlarged.

On the Ufe of Oak Leaves in HetHoufes in Preference to Tanners Bark, by W. Speechly, Gardener to his Grace the Duke of Portland.

Prefume that the leaves of the eak abound with the fame qua lity as the bark of the tree, therefore the fooner they are raked up after they fall from the trees, the better, as that quality will naturally decreafe daring the time they are expofed to the weather. After being raked into heaps they should immediately be carried to fome place near the hot-houses, where they muft lie to couch. I generally fence them round with charcoalhurdles, or any thing else to keep them from being blown about the garden in windy weather. In this place we tread them well, and wa ter them in cafe they happen to have been brought in dry. We

make

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