On the different colours of the metallic oxides, with an application of these principles to the Arts.

I shall now proceed to offer for your further consideration a few remarks on the different colours of the metallic oxides, with an application of these principles to the Arts.-When metals are oxided by means of heat, "they are converted into earthy-like powders of different colours and properties." The origene gas during calcination is absorbed by the metal, and the oxigene and the light, (constituents of oxigene gas) become fixed in the oxide according to the degree of heat employed; for the oxide assumes the violet coloured ray first, and by increasing the temperature, the violet colour is thrown off, in consequence of its being the weakest, or the most refrangible ray: in like manner some oxides assume in rotation the different colours, according to their respective refrangibilities, and they are dissipated in that ratio to the increase of heat: the red ray, the strongest and the most difficult of refrangibility, requires still a higher temperature than the other six constituent colours of light, and from its greater affinity to oxigene than the other rays of light, it is not so easily driven off, hence the red ray becomes fixed in the oxide, which constitutes its red colour, while the heat and the other six constituents of light are set at liberty even this red ray may be driven off by increasing the heat, and then the red oxide is converted into white.-According to the experiments of Macquer, he oxided gold with a burning glass, more powerful than that of Tschirnhausen, and remarked that the oxide assumed the violet colour.-If it were possible to increase the temperature sufficient to produce the red oxide of gold, it appears reasonable to infer that all the intermediate coloured oxides of this metal, might be made, provided the heat could be applied in that proportion or degree to the different refrangibilities of the various colours. This doctrine is eminently supported, by the process employed to make vermilion.-If we take four ounces of sublimed sulphur and fuse it in an unglazed earthen pot, and to this add one pound of mercury, and let it be mixed with the sulphur by stiring or agitation. When these substances have combined to a certain

degree, the mixture spontaneously takes fire, and is suffered to burn about a minute. The flame is then smothered, and the residue pulverised, which forms a violet powder. This powder being sublimed, affords a sublimate of a livid red colour, which when powdered, exhibits a fine red colour, known by the name of vermilion."-Here it is very obvious, that the high degree of heat, necessary to produce this sublimate, dissipated the violet colour, in consequence of its great refrangibility, and fixed the red ray in the oxide, which constitutes the vermilion colour.-To these I could add numberless facts, on the different coloured oxides of the different metals, in support of the doctrine which I have adopted, "but no more causes are necessary than are sufficient to explain the phenomena."-Hence this. exposition most elegantly proves and illustrates the doctrine of Sir Isaac Newton, on the seven different rays of light, and their different refrangibilities and reflexibilities.

It must now appear very evident, that a knowledge of these principles, and an application of them to the arts, would in a very great degree assist the manufacturers, and particularly those who work in porcelain, china, glass, and in all kinds of pottery, to burn in, and fix the different colours, according to their different refrangibilities.-That is to say, the degree of heat which would be necessary to fix permanently the red colour, would be a temperature so high, as to burn out and dissipate, all the other colours, provided all the seven coloured oxides, were made from the same metal, and painted on a piece of porcelain; therefore to avoid an error of this kind, the manufacturer would be obliged to burn in the red colour first, secondly the orange, thirdly the yellow, fourthly the green, fifthly the blue, sixthly the indigo, and seventhly and lastly, the violet colour; for by an attempt to burn in and fix the violet colour first, and afterwards to burn in the red, before the latter could be accomplished, the former would be dissipated.-Therefore it is necessary to know that the degree of heat sufficient to produce the violet coloured oxide of gold, would be of so high a temperature as to drive off all colour from the red oxide of lead, and convert it into a white litharge: hence when several colours are to be fixed in, or burnt on porcelain at the same.

time, the different coloured oxides from the different metals should be selected, which would all bear the same degree of heat. Say 1300 degrees of Fahrenheit's thermometer, consequently no two oxides of different colours from the same metal would answer, therefore a knowledge of these principles and their application, would enable the manufacturer to adorn and beautify his wares, and to bring to greater perfection the dif ferent branches of the arts,

No. XLI.

Observations of the eclipse of the sun, June 16th, 1806; made at Lancaster, by Andrew Ellicott Esquire,

Read August 15th, 1806.

Lancaster, August 1st, 1806.

DEAR SIR,

THE following observations, which I request the favour of you to hand to the Philosophical Society, were made at this place on the solar eclipse of the 16th of June last.

The morning was cloudy till about 9 o'clock, when the sun became visible through thin flying clouds: a short time before the beginning of the eclipse, the clouds were so far dissipated, that the limb of the sun was very distinct, and well defined. At 9 53′ 8′′ A. M. apparent time, the eclipse began; the first impression made by the moon was at the point expected, and to which my eye was constantly directed.-The end of the eclipse was at 0 18′ 56′′ P. M. apparent time.-A few minutes after the eclipse began, the clouds increased so much as to prevent any measures between the points of the cusps or horns being taken till 10 44′ 25′′, when the following series commenced.

L

The irregular decrease and increase of the distances between the points of the cusps, is greater than would arise in so excellent a micrometer from the small imperfections inseparable from such observations. These irregularities were principally occasioned by the uneven surface of the moon, particularly that part, which formed the southern cusp or horn.-The northern cusp was well defined, and finely terminated, but the southern one was sometimes obtuse, at others terminated by a parallel thread of light, which disappeared from one end to the other, at the same time; and frequently one or two luminous points of the sun's limb, were observed to be completely detached from the point of the cusp.-The most remarkable of these phenomena was observed between 10 52', and 10 55'. To give some idea of this appearance, let the circle A B C D Fig. 2d, Pl. VI. represent the periphery of the sun's disk, and EBFD that of the moon's: the line EAFC a vertical, supposed to

pass through the centre of the sun:-then B will represent the point of the southern cusp. At about 10 53′ the point of the cusp appeared as in Fig. 3, the thread of light, a b, disappeared from one end to the other, at the same instant, the point of the cusp then appeared as in Fig. 4.-In a very short time the thread of light which connected b with the body of the cusp disappeared, and left b visible for a number of seconds, after it was detached from the other visible part of the sun. The cusp then appeared very obtuse, as represented in Fig. 5 which was observed by those who were using the most indifferent glasses.

Those detached luminous points of the sun's limb, seemed to retain their brilliancy, till the instant of their disappearance, which it would appear should not have been the case, if the moon was surrounded with an atmosphere:-those points particularly, which were formed by depressions in the moon's limb, would have had their splendor somewhat diminished, by the density of the atmosphere, if one existed :-but nothing of the kind was observed..

The sun's diameter was found by a great number of observations, made both on the day of the eclipse, and the day preceding, to be 58, divisions of the micrometer:-the denominator of the fractional part of a division being constantly 50 the numerators only are entered in the observations.When the first measures were taken, a line joining the points of the cusps passed nearly through the centre of the sun-in that situation it will easily be seen that the distances must remain for a few minutes so nearly the same, that but little advantage can be drawn from the observations; on this account I have only made out the results of twelve observations on each side of the measure, taken at 10 55′ 27′′, which turns out accidentally to be, not only the middle observation, but the shortest observed distance between the points of the cusps:the first and three last observations, are therefore omitted in the calculations. These observations may be so varied, as to furnish a great number of results, because any two, however taken, on different sides of the apparent conjunction, may be considered almost equivalent to the observation of an eclipse,