knife, and washed with milk and egg where he had occasion to make it smooth. and even when dry he painted it, mixing the colours with common water; this on being placed horizontally in an oven, only warm enough to melt the wax, flaked from the board; but held so much better together than any of the former, that he pasted part of it on paper.

Exper. 7.-Flake white mixed with egg and milk, crumbled all to pieces in the oven when put on the waxed board, as in the last experiment. The badsuccess which had attended all the former experiments, led him to consider of what use the wax was in this kind of painting; and it occurred that it was only as a varnish to preserve the colours from fading. In order to try this,

Exper. 8. He took what the bricklayers call fine stuff, or putty; to this he added a small quantity of burnt alabaster to make it dry: this it soon did in the open air; but before he put on any colours, he dried it gently by the fire, lest the colours should run. When it was painted, he warmed it gradually by the fire, to prevent the ground from cracking, till it was very hot. He then took white wax 3 parts, white resin one part, melted them in an earthen pipkin, and with a brush spread them all over the painted board, and kept it close to the fire in a perpendicular situation, that what wax and resin the plaster would not absorb might drop off. When cold, he found the colours were not altered, either from the heat of the fire or passing the brush over them. He then rubbed it with a soft linen cloth, and thus procured a kind of gloss, which he afterwards increased by rubbing it with a hard brush; which was so far from scratching or leaving any marks on the picture, that it became more smooth and po lished by it.

After he had made all the foregoing experiments, in conversation with Dr. Kidby, who told him that there was a passage in Vitruvius de Architectura relative to that kind of painting; and which, when translated, runs thus: "But if any one is more wary, and would have the polishing [painting] with vermilion hold its colour, when the wall is painted and dry, let him take Carthaginian [Barbary] wax, melted with a little oil, and rub it on the wall with a hair pencil; and afterwards let him put live coals into an iron vessel (chafing dish,) and hold it close to the wax, when the wall, by being heated, begins to sweat; then let it be made smooth: afterwards let him rub it with a candle and clean linen rags, in the same manner as they do the naked marble statues. This the Greeks call xavis. The coat of Carthaginian wax, thus put on is so strong, that it neither suffers the moon by night, nor the sun-beams by day to destroy the colour." Being satisfied, from this passage in Vitruvius, that the manner of using wax in Exper. 8 was right, Mr. C. was now to find if the wax-varnish, thus burnt into the picture would bear washing: but here he was a little disappointed; for rubbing one corner with a wet linen cloth, some of the colour

καυσις.

came off; but washing with a soft hair pencil dipped in water, and letting it dry without wiping, the colours stood very well, A board, painted as in Exp. 8, was hung in the most smoaky part of a chimney for a day, and exposed to the open air in a very foggy night. In the morning the board was seemingly wet through, and the water ran off the picture. This was suffered to dry without wiping, and the picture had not suffered at all from the smoke of the dew, either in the ground or the colours: but when dry, by rubbing it first with a soft cloth, and afterwards with a brush, it recovered its former gloss.

Suspecting that some tallow might have been mixed with the white wax he had used, which might cause the colours to come off on being rubbed with a wet cloth, he took yellow wax which had been melted from the honeycomb in a private family, and consequently not at all adulterated; to 3 parts of this he added one part resin, and melted them together.

Exper. 9.-Spanish white, mixed with fish glue, was put for a ground on a board and painted with water colours only. The board was made warm; and then the wax and resin were put on with a brush, and kept close to the fire till the picture had imbibed all the varnish, and looked dry. When cold, he rubbed it first with a linen cloth, and then polished it with a hard brush.

IX. On the Success of the preceding Experiment. In a Letter from Mr. Josiah Colebrook, F. R. S. p. 53.

This short letter accompanies a specimen of the encaustic on paper, being a bird drawn by Mr. George Edwards, on paper prepared with a ground of whitening and fish-glue, painted with water colours, and then the wax, &c. burned in. This will roll up as easily as common paper, without cracking the varnish. There are also 2 landscapes, painted by a young lady, after the same manner, on wood.

X. Of a Particular Species of Cocoon,* or Silk Pod, from America. By the Rev. Samuel Pullein, M. A. p. 54.

Having lately seen the aurelia of a particular species of caterpillar, Mr. P. judged, from its texture and consistence, that there might be procured from it a silk not inferior to that of the common silk-worm in its quality, and in its quantity much superior. He made some experiments on this new species of silk pod, which strengthen this opinion. This pod is about 34 inches in length, and above one inch in diameter; its outward form not so regular an oval as that of the common silk worm; its consistence somewhat like that of a dried bladder, when not fully blown; its colour of a reddish brown; its weight 21 grains.

* Several of the large moths of the Linnean division attaci form similar pods, in which they undergo their chrysalis state, as the phalæna Atlas, Hesperus, &c.

On cutting open this outer integument, there appeared a pod completely oval, as that of the silk-worm. It was covered with some floss-silk, by which it was connected to the outer coat, being of the same colour. Its length was 2 inches; its diameter nearly one inch; and its weight 9 grains. The pod could not be easily unwound, because it was perforated by the moth: but on putting it in hot water, he reeled off so much as sufficed to form a judgment of the strength and staple of its silk. The single thread winded off the pod in the same manner as that of the common silk-worm; seeming in all respects as fine and tough. He doubled this thread so often as to contain 20 in thickness; and the compound thread was as smooth as elastic, and as glossy as that of the common silk-worm. He tried what weight it would bear; and it bore 15 oz., and broke with somewhat less than 16, on several trials. He then tried a thread of the common silkworm, which was also composed of 20 (in thickness it rather exceeded the other); and it broke always with 15 oz. He boiled a part of the cocoon in water for 4 hours, that he might know whether it was composed of a gum in any sort mucilaginous; and he found that it was as indissoluble as that of the common silkworm. The common silk-pod, with all its floss, weighs usually but 3 grains: and here is a pod which weighs 7 times as much. If the outer coat, which weighed 12 grains, were all to be used only as floss-silk, there remain 9 grains capable of being reeled; which is above 3 times as much as can be reeled from the common cocoon. But he is of opinion, that when the pod is fresh, and not hardened by age, the whole outer coat may be reeled off: for the pod on which he made these trials was 7 or 8 years old.

On inquiry, he found that the moth of this pod is called the isinglass by Marian. It is a very large moth, being 5 inches from the tip of each wing extended. It differs from the silk moth in having a proboscis, which intimates that it feeds in its papilio state, whereas the silk-moth never eats. The caterpillar which produces this pod is a native of America. It was found in Pennsylvania: the pod was fixed to the small branch of a tree, which seemed to be either of the crab or hawthorn species. The leaf of the tree had also helped to support the pod; for the mark of its ribs was apparent on the surface of the pod. XI. A Thermometrical Account of the Weather, for One Year, beginning September 1753. Kept in Maryland, by Rich. Brooke, M. D. Communicated by Mr. Henry Baker, F. R. S. p. 58.

Merely a journal of the thermometer, with the weather, as to winds, rains, snow, &c.

XII. A Thermometrical Account of the Weather, for Three Years, beginning September 1754, as observed in Maryland. By Rich. Brooke, M. D. p. 70. This is of the same nature as the preceding article.

XIII. Electrical Experiments and Observations. By Edward Delaval, M. A. p. 83.

Mr. D. filled several small glass tubes with the dry powders of calcined metals, viz. ceruss, lead ashes, minium, calx of antimony, &c. Into each end of every tube he put a piece of iron wire, which communicated with the calx, and fastened them with wax: so that the electric fluid, not being able to escape by means of the glass, must either pass through the calx, or not at all. On hanging one of the wires, bent for the purpose, to the electrified bar, and holding the other in his hand, he observed that no electric matter passed the calx, the snaps issuing all the while from the bar, or from that wire which was in contact with the bar. Animal and vegetable solids also, when reduced to ashes, and interposed in the same manner between two pieces of wire, he found as effectually intercept the electric stream, as the metallic calces. From these experiments we see, that animal, vegetable, and metallic bodies, though such known conductors of the electric fluid while in their entire state, are easily changed into resisters, or non-conductors of it.

Mr. D. was led to attempt this change from its having been observed, that dry mould would not conduct the electric fluid; and thence he suspected, that one class of the non-conductors must owe its property to an electrical virtue that would be found to reside in the calx, or earth of the chymists, after it is divested of the unctuous inflammable matter, which constitutes another of the chymical principles called sulphur; in like manner as this sulphur is constantly found highly electrical in all bodies where it abounds in a solid form, viz. resins, wax, &c. It must be remembered, that there is a remarkable and well-known opposition to the electrical effects of these two classes; the earthy one (as glass and stones) electrifying plus, and the sulphureous one minus. Does it not seem then a thing to be expected, in a body compounded of both, that the opposite powers of these ingredients should counterbalance and destroy the effects of each other, and the body in which the positive and negative ones equally prevail, become neutral, or non-electric?

There is another process, natural and without fire, which is supposed to destroy the sulphureous substance of metals, viz. when they are corroded, and moulder in the open air. Accordingly, with the same apparatus in which I tried the calcinations by fire, I examined the common rust of iron, and flakewhite, which is the rust of lead, and find them equally converted into non-conductors in the open air. That this change, in metals particularly, is not owing to, or promoted by, the circumstance of mere pulverization, is evident, not only because the above-mentioned calces are equally strong electrics when formed into hard masses with a thin paste of flour and water, and after

wards dried, but most clearly because the finest filings or powders of metals conduct as readily as the entire substances do.

But though this change will not succeed in metallic substances on mere pulverization, yet it seems to follow in most other hard bodies. Having dried a piece of Portland stone, he found it conducted perfectly, well; but on powdering, and sealing it up in one of the tubes with the wire ends, as above, it became a perfect resister, or non-conductor, like the metallic calces. He tried the same experiment on a variety of other bodies, particularly gum arabic and alum; and had reason to believe it will succeed in all bodies that can be pulverized in the mortar.

Another very extraordinary means of making this change in bodies, which abound in calx or earth, is by fire, not by the intense one that calcines, but by a moderate heat; their most perfect resistance, or non-conducting property, being when their heat is just tolerable to our hands. Mr. D. had some of the same Portland stone, wrought into plates nearly as thin as window-glass, which he heated to a proper degree, and then coated on both sides with metal, in order to make the Leyden experiment. When the stone is hot enough to singe paper, it conducts as perfectly as when cold; but on cooling a little, it begins not to conduct, and affords small shocks, which gradually increase in strength for about 10 minutes; at which time it is about its most perfect state, and remains so near a quarter of an hour: after that time the shocks. gradually decrease as the stone cools, till at last they quite cease, and it returns to its conducting state again; but this state appears before the stone is quite cold.

Experiments of this kind succeed in all bodies abounding in calx or earth, as stones dried clay, wood when rotten or burned in the fire till the surface becomes black. Among other substances, he tried a common tobacco-pipe, part of which near the middle he heated to a proper degree, and then applied one end of it to the electrified bar, while the other was held in the hand; and he observed that the electric fluid passed no farther along the pipe than to the heated part.

XIV. The Case of Wm. Carey, aged 19, whose Tendons and Muscles were turning into Bones. By the Rev. William Henry, D. D., F. R. S. Dated Castle-Caldwell, near Enniskillen, March 1, 1759. p. 89.

Wm. Carey was born in an island in Lough Melvill, a large lake in the northern point of the county of Leitrim in Ireland, and had continued there, or in the adjacent lands ever after. He was bred up to work as a labourer, and continued in very good health from his birth until 2 years before the above date. About