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&c.; and that only calcination discharges them. Therefore it is probable that Mr. Chambers's method of staining or colouring marbles is extremely good.
Though acid menstrua work greatly on marble, yet it is observable that these colours are not discharged by them, but only by calcination; which, as it entirely and thoroughly destroys the compages of the stone, the substances of the colours must undoubtedly at the same time be exhaled by the force of the fire. We observe a like process in the works of nature; viz. in the dendritæ, or such as are on alkaline stones: for though the stones are utterly corroded by the acids, yet the dendritæ, however merely superficial, remain; but if calcined, the said dendritæ are immediately exhaled, and entirely disappear.
This art will not only give pleasure to the eye by regular paintings (whereas the natural colourings of marble are very irregular) but it may be very useful to blazon arms, and for inscriptions; as sculpture alone can never express colours, and chisseled inscriptions, &c. suffer much by age; for probably a monument of marble, rightly coloured by this method, will be preserved many ages from the injuries of the weather, though at the same time the stone itself will be somewhat hurt or corroded by the air.
VI. Observations on the Sea Scolopendre, or Sea Millepes.* By John Andrew Peyssonel, M. D., F. R. S. Translated from the French. p. 35.
This creature, in its figure, is like the land scolopendre, or, as Pliny says, to the hairy caterpillar, commonly called the milleped animal. It is of the same colour, has the same arrangement of circular rings; but whereas the land scolopendre is flat, this is square. Dr. P. counted 80 rings, which form the body and head, when brought to him. This sea insect was very small, and almost imperceptible. He was surprised, after having kept it some time, to see a round body, of a blackish green colour, like the glans virilis, pass out of it, which had a considerable opening, like the canal of the urethra. This gland was surrounded by two bodies or bowels, which appeared in form of a prepuce turned back; the one was yellowish, and the other whitish; each but a line thick, stronger and larger above, and terminating below like a ligature, filled with a matter like that contained in the intestines of fishes and insects. This may be what gave occasion to Pliny, and other naturalists, to think, that these insects, finding themselves taken, throw out their bowels in order to lessen their bulk.
The body of the animal is square; and the 4 sides are armed with such prickles as he never saw before. Also every ring has 4 bundles of prickles. The following is the manner of their being disposed: at the end of each ring, above the square, on each side we see a gland, near which a bundle of prickles arises
* The animal here described seems to belong to the genus terebella.
towards the squares below. This bundle seems to fill the whole ring, and to part as it were from the centre of the under side; where is a hollow or separation, which passes in a right line from the head to the tail. The bundles of prickles appear round at first, and terminate in points; but afterwards they are seen to spread out like a fan; so that their extremities are more than 4 times the breadth of their bases. They contain an infinite number of prickles, which are extremely fine, loose, and brilliant, like an aigrette of glass, but more free and loose. The range of prickles underneath spreads also like fans, serving the insect as feet; for it is on these he stands, and moves on them as the scolopendre does on his feet. Having put these sea scolopendres on his fingers, they thrust a great number of their prickles into the skin, and caused a sharp pain for some hours: it was like fire on the part. It was in vain that he rubbed and washed. the part; and though the prickles were broken, yet the parts that stuck in the flesh produced their effect, and caused the pain he felt for some hours. Afterwards it all went off without any further ill consequence..
VII. On a Storm of Thunder and Lightning at Norwich, July 13, 1758. By Mr. Samuel Cooper. p. 38.
About 4 o'clock on Thursday afternoon, July 13, 1758, a short but severe thunder storm, with lightning, fell on the top of a house standing alone, and. belonging to a common garden, on the causeway near Sandling's ferry, in the city of Norwich; it struck off the tiles of the roof at the east end, to the space of a yard or two; burnt a very small hole in the middle of a lath, in piercing into the chamber, and then darted to the north-east; ripped off the top of an old chair, without throwing it down; snapped the two heads of the bed-posts, rent the curtains, drove against the wall (the front of the house stands due northeast) forced out an upright of a window frame a yard long, 3 inches broad, and 2 thick; smote it in a right line into an opposite ditch, 10 or 12 yards distant:: then struck down on the wall of the chamber, paring off half a foot's breadth of its plastered covering quite down to the floor; lifted up a board of the floor, and leaving a hole of half an inch diameter, pierced through by the side of the main beam into the kitchen, towards the west end of a pewter shelf; traversed the whole shelf to the east, and melted superficially, to the breadth of a shilling, 6 pewter dishes, 2 plates, and a pewter basin, all standing touching each other: 2 of the dishes were thrown down, the rest not displaced.. Under this, a narrower shelf of pewter plates untouched. In its descent to the floor, knocked down, as she expressed it, an ancient woman sitting in the passage westward of
* This account is confirmed in almost every circumstance by another communicated to the Royal Society in a letter from Mr. William Arderon, F. R.S. to Mr. Henry Baker, F. R.S.-Ori
the shelves; who being presently taken up, her shoulders and back were found to be scorched all over, with the hind part of her left leg; the skin almost universally red and inflamed, rimpled in two or three places, but not broken: her shift burnt brown, stocking singed, with its colour of the inside discharged, and the outside unchanged: right foot very painful and bruised, with that shoe struck off, and its upper leather torn: her gown and other clothes without any damage. It passed through the same passage without injuring another old woman sitting knee to knee with her companion; but keeping its direction to the north-east, turned on a right angle on the outer door, split it, and passed through into the open air. On a right line with this passage to the west, and under the same roof, is the wash-house, where stood the master and his man. They saw the woman tumble down, and heard such a violent explosion, that made them both think the whole house must come down: and the man says, with such a blaze, as if all was on fire, but that was but for a moment. To the cast of the pewter shelves, and under that part of the roof where it entered, it rushed into the kitchen closet, by tearing off a wooden button, that was nailed on, and there took some pieces from a Delft dish without throwing it down, broke a quart mug, and from a 4-ounce phial half full of oil cut off its empty half part without spilling a drop of the oil. The activity of the lightning was with abated violence to all other points of the compass; but not without some considerable degree of force; for it scraped the plaster off the wall in many different and distant places, both in the chamber and kitchen, and to the south-west of the chamber, where was the window, broke many panes of glass, and tore the lead outwardly, without melting it; and broke two panes of the kitchen window, with its lead, situated under the chamber window. Both kitchen and chamber smelt as strong of sulphur some hours after, as if fumigated with brimstone matches.
VIII. Experiments concerning the Encaustic Painting of the Ancients. By Mr. Josiah Colebrooke, F. R. S. p. 40.
The art of painting with burnt wax, as it is called, has long been lost to the world; the use of it to painters, in the infancy of the art of painting, was of the utmost consequence, drying oil being unknown, they had nothing to preserve their colours entire from the injury of damps, and the heat of the sun; a varnish of some sort was therefore necessary; but, being unacquainted with distilled spirits, they could not, as we now do, dissolve gums to make a trans-. parent coat for their pictures; this invention therefore of burnt wax supplied that defect to them, and with this manner of painting, the chambers and other rooms in their houses were furnished; this Pliny calls encaustum, and we encaustic painting.
The following experiments were occasioned by the extract of a letter from the
Abbé Mazeas, translated by Dr. Parsons, and published in the 49th volume of the Philos. Trans. concerning the ancient method of painting with burnt wax, revived by Count Caylus. The Count's method was, First, To rub the cloth or board designed for the picture simply over with bees-wax. Secondly, To lay on the colours mixed with common water; but as the colours will not adhere to the wax, the whole picture was first rubbed over with Spanish whitening,* and then the colours are used. Thirdly, When the picture is dry, it is put near the fire, by which the wax melts, and absorbs all the colours.
Exper. 1.-A piece of oak board was rubbed over with bees-wax, first against the grain of the wood, and then with the grain, to fill up all the pores that re
mained after it had been planed, and afterwards was rubbed over with as much dry Spanish white, as could be made to stick on it, this, on being painted (the colours mixed with water only) so clogged the pencil, and mixed so unequally with the ground, that it was impossible to make even an outline, but what was so much thicker in one part than another, that it would not bear so much as the name of painting; neither had it any appearance of a picture; however, to pursue the experiment, this was put at a distance from the fire, on the hearth, and the wax melted by slow degrees; but the Spanish white (though laid as smooth as so soft a body would admit, before the colour was laid on) yet on melting the wax into it, was not sufficient to hide the grain of the wood, nor show the colours by a proper whiteness of the ground, the wax in rubbing on the board, was unavoidably thicker in some parts than others, and the Spanish white the same: on this he suspected there must be some mistake in the Spanish white, and made the inquiry mentioned in the note below.
To obviate the inequality of the ground in the first experiment.
Exper. 2.-A piece of old wainscoat (oak board) of an inch thick, which having been part of an old drawer, was not likely to shrink on being brought near the fire; this was smoothed with a fish-skin, made quite warm before the fire, and then with a brush dipped in white wax, melted in an earthen pipkin smeared all over, and applied to the fire again, that the wax might be equally thick on all parts of the board, a ground was laid on the waxed board with levigated chalk mixed with gum water, viz. gum Arabic dissolved in water; when dry, he painted it with a kind of landscape, and pursuing the method laid down. by Count Caylus, brought it gradually to the fire by slow degrees, till it came within 1 foot of the fire, which made the wax swell and bloat up the picture;
Spanish chalk is called by Dr. Parsons, in a note, Spanish white; this is a better kind of whitening than the common, and was the only white that had the name of Spanish annexed to it, that he could procure, though he inquired for it at most if not all the colour shops in town. Mr. Dacosta showed him a piece of Spanish chalk in his collection, which seemed more like a cimolia (tobacco pipe clay) and was the reason of his using that in one of the experiments.-Orig.
but as the chalk did not absorb the wax, the picture fell from the board and left it quite bare.
Exper. 3.-He mixed 3 parts white wax, and one part white resin, hoping the tenacity of the resin might preserve the picture. This was laid on a board. heated with a brush, as in the former; and the ground was chalk, prepared as before. This was placed horizontally on an ironing box, charged with a hot heater, shifting it from time to time, that the wax and resin might penetrate the chalk; and hoping from this position that the ground bloated by melting the wax, would subside into its proper place: but this, like the other, came from the board, and would not at all adhere.
Exper. 4.-Prepared chalk 4 drams, white wax, white resin, of each a dram, burnt alabaster half a dram, were all powdered together and sifted, mixed with spirit of molosses instead of water, and put for a ground on a board smeared with wax and resin, as in Exp. 3. This was also placed horizontally on a boxiron, as the former: the picture blistered and was cracked all over; and though removed from the box-iron to an oven moderately heated, in the same horizontal position, it would not subside, nor become smooth. When cold, he took an iron spatula made warm, and moved it gently over the surface of the picture, as if to spread a plaster. This succeeded so well, as to reduce the surface to a tolerable degree of smoothness: but as the ground was broken off in many places, he repaired it with flake white, mixed up with the yolk of an egg and milk, and repainted it with molosses spirit, instead of water; and then put it into an oven with a moderate degree of heat. In this he found the colours fixed, but darker than when it was first painted; and it would bear being washed with water, not rubbed with a wet cloth.
Exper. 5.-A board that had been used in a former experiment, was smeared with wax and resin, of each equal parts; was wetted with molosses spirit, to make whitening (or Spanish white) mixed with gum-water adhere. This, when dry, was scraped with a knife, to make it equally thick in all places. It was put into a warm oven, to make the varnish incorporate partly with the whitening before it was painted; and it had only a small degree of heat: water only was used to mix the colours. This was again put into an oven with a greater degree of heat; but it flaked off from the board.
Exper. 6. Having miscarried in these trials, he took a new board, planed smooth, but not polished, either with a fish-skin or rushes: he warmed it, and smeared it with wax only; then took cimolia (tobacco-pipe clay) divested of its sand, by being dissolved in water and poured off, leaving the coarse heavy parts behind. After this was dried and powdered, he mixed it with a small quantity of the yolk of an egg and cow's milk, and made a ground with this on the waxed board. When the ground was near dry, he smoothed it with a pallet