ject as being very laborious, and in its practical application difficult to be established. Under fuch impreffions, much is not to be expected in the progrefs. It feems nevertheless that mankind have rejected universal characters when offered to them, not because they were averse from the means of facility and perfpicuity, but because those means were not in reality difplayed. The Arabic numerals, the notation of mufic, and the fymbols of quantity and operation used by algebraifts, are universal characters confined to no language, and have been universally received because they are fimple and appropriate; but the characters of chemists, as well as the few attempts at the more ample defignation of things in the fame manner, have not been received, because their authors have stopped fhort in their use and adaptation." If Bishop Wilkins, and the great men of the laft century who favoured his univerfal character, had studied and used it to fuch an extent as to have written treatises according to that notation; or if the great Bergman had attempted a reform in the characters of chemistry, and adopted such as could be readily formed, easily distinguished, and compounded, with all the advantages of pofition, of which he was fo well aware; if he had completed a fet of tables exhibiting the whole of chemical fcience, and expreffing things, quantities, actions, temperatures, and other habitudes, in a few pages, which those who attentively meditate on his compound tables of elective attraction may without difficulty conceive to be poffible; the lovers of that science would have learned to read his work, and to write others according to the fame method; and that for reafons of the fame kind as have induced arithmeti cians, musicians, and algebraifts, to become mafters of the univerfal characters proper to their respective sciences.-16. On the Process of Bleaching with the Oxygenated Muriatic Acid, and a Description of a new Apparatus for Bleaching Cloths with that Acid diffolved in Water, without the Addition of Alkali. By Theophilus Lewis Rupp.-17. Account of a remarkable Change of Colour in a Negro. By Miers Fisher. This man's father was the fon of a native African and an Indian of Philadelphia. His mother was the daughter of an African man and an Irish woman. By a certificate here exhibited, it appears, that until the month of February 1792, being then at least 30 years old, he was of as dark a complexion as any African; at which period his skin began to change white, like that of an European, commencing at his fingers' ends, and proceeding, chiefly in the fummer or warm weather, over the rest of his body. The greater part of the furface was thus changed at the time of the account being written, which was the 22d of November 1796. The change was not uniform over the whole furface, but gradually progreffive along the fkin; the black and white parts being separated by an irregular line. No facts are mentioned in explanation of this remarkable change.

Tranfactions of the Royal Society of Edinburgh, Vol. IV. Quarto. 470 pages, with 12 plates. Printed for Cadell and Davies in London; and Dixon and Balfour, Edinburgh, 1798.

This work is divided into three parts.

Part I. contains the Hiftory of the Society, or Reports concerning Memoirs prefented, and Communications made, with a Lift of the Officers and Members, Donations, and other fimilar Particulars. It alfo contains Biographical Accounts of Lord Abercromby; of William Tytler, Efq. of Woodhoufelee; of Mr. William Hamilton, late Profeffor of Anatomy and Botany in the University of Glasgow; and of John Roebuck, M. D.

Part II,

Part II. contains, I. Papers of the Phyfical Clafs.-1. Account of a Mineral from Strontian, and of a peculiar Species of Earth which it contains. By Thomas Charles Hope, Profeffor* of Medicine in the University of Glasgow.-2. Obfervations on the Natural History of Guiana. By William Lochead, Efq.-3. On the Principles of the Antecedental Calculus. By James Glenie, Efq.-4. Obfervations on the Trigonometrical Tables of the Brahmins. By John Playfair, Profeffor of Mathematics in the University of Edinburgh.-5. Some Geometrical Porifms, with Examples of their Application to the Solution of Problems. By Mr. William Wallace, Affiftant Teacher of the Mathematics in the Academy of Perth.— 5t. On the Latitude and Longitude of Aberdeen. By Andrew Mackay, LL.D. & F.R.S. Edin.-6. An Account of certain Motions which small lighted Wicks acquire when swimming on a Bason of Oil. By Patrick Wilfon, F.R.S. Edin. and Profeffor of Practical Aftronomy in the Univerfity of Glasgow. (See Philof. Journal, II. 167.)-7. Account of a fingular Halo of the Moon. By William Hall, Efq. of Whitehall, F.R.S. Edin.-8. A New Series for the Rectification of the Ellipfis, with Obfervations on the Evolution of a certain Algebraic Formula. By James Ivory, A.M.-9. Mineralogical Description of the Mountain of Gibraltar. By Major Imrie.-10. Defcription of a Thermometer, which marks the greatest Degree of Heat and Cold from one Time of Observation to another. By Alexander Keith, Efq. F.R.S. & F.A.S. Edin.-11. Defcription of a Barometer which marks the Rife and Fall of the Mercury from two different Times of Observation. By Alexander Keith, Efq. F.R.S. & F.A.S. Edin.-12. Meteorological Abstract for the Years 1794, 1795, 1796. II. Papers of the Literary Clafs.-I. On the Origin and Principles of Gothic Architecture. By Sir James Hall, Bart. F.R.S. & A.S.S. Edin.-2. M. Chevalier's Tableaude la Plaine de Troye illuftrated and confirmed from the Obfervations of fubfequent Travellers and others. By Andrew Dalzel, M.A. F.R.S. Edin. Profeffor of Greek in the University of Edinburgh.

Now Joint Profeffor of Chemiftry in the Univerfity of Edinburgh.

By mistake, No. 5.is repeated.

A

JOURNAL

OF

NATURAL PHILOSOPHY, CHEMISTRY,

AND

THE ARTS.

AUGUST 1798.

ARTICLE I.

Farther Experiments and Observations on the Affections and Properties of Light.
By HENRY BROUGHAM, jun. Esq.

[Concluded from Page 155 of the present Volume.]

Obfervation 5.

THE direct light falling on the fpeculum, and part of the reflected light on the horizontal

white ftage of a very accurate micrometer, I measured the breadth of the fringes, fpots, &c. Thefe, with the distance of the fpeculum from the window and micrometer, and the fize of the fun's image, are fet down in the following table, all reduced to inches and decimals.

In the image where these measures were taken, there were feven other elliptic fpots, a Jittle lefs and nearly equal; all the others were much smaller and more confused.

Obfervation 6. On viewing the furface of the fpeculum attentively in that place whence the rays formed the oblong and firft mentioned elliptic fpots, I faw a dark but very thin long fcratch, and a dark dent, fimilar in fhape to the dark spaces on the image; the dark spot measured less than of an inch; which makes its whole furface to the whole polished furface, as 1 to 34225, fuppofing the former circular or nearly fo. All these measures will be found to agree very well, for their smallness and delicacy: thus, the ratio laft mentioned is nearly the fame which we obtain by comparing the image and the spot: the like may be faid of the two fpots mentioned in the table, i. e. their axes are proportional. I now could produce what fpots I pleafed, by gently fcratching the fpeculum, or by making lines, dots, &c. with ink, and allowing it to dry; for these last formed convex fibres, which produced coloured fringes as well as the concavities, agreeably to what was deduced a priori.

209

763

2

Obfervation 7. The whole appearance which I have been defcribing bore fuch a close and complete refemblance to the fringes made round the shadows of bodies, that the identity of the cause in both cafes could not be doubted. In order, however, to fhew it ftill further, I measured the breadths of two contiguous fringes in feveral different fets: the measurements agreed very well, and gave the breadth of the firft fringe .0056, and of the fecond .0034; or of the first .0066, and of the fecond .0034. The ratio of the breadths by the first is 28 to 17; by the fecond, 30 to 17; of which the medium is 29 to 17: and this is precifely the ratio of the two innermoft fringes made by a hair, according to Sir Ifaac Newton's meafurement; the first being, according to him, of an inch; the fecond, of an inch *. Farther, the two innermoft rings made by plates have their diameters (not breadths) in the ratio of 1 to 2 t, and the diftance between the middle of the innermoft fringes (made by a hair), on either fide the fhadow, is to the fame diftance in the fecond fringes as to 7 i therefore, the diameters of the two first rings made by the specks in the fpeculum, are as to; which ratio differs exceedingly little from that of 1 to 2, the ratio of the diameters of rings made by plates, either thofe called by Newton thick, or those which he names thin: for fuppofe this difference nothing, 23x203 = 16×177; and the difference between these two products (now stated equal) is not much above 3 in reality. Obfervation 8. The laft thing worth mentioning in these phenomena was this: I viewed the fringes through a prifm, holding the refracting angle upwards, and the axis parallel to that of the dark space; then moving it till the objects ceased descending, I faw in that posture the fringes much more diftinct and numerous; for I could now see five with ease, and feveral more less diftinctly. This led me to try more minutely the truth of the 5th propofition, with respect to the number of the fringes furrounding the fhadows of bodies in direct light. Having produced a bright set of these by a blackened pins of an inch in diameter, I viewed them through a well made prifm, whofe refracting angle was only 30°, and held this angle upwards, when the fringes were on the fide of the fhadow opposite to me. I then moved the prifm round on its axis; and when it was in the posture between the afcent and defcent of the objects, I was much pleafed to fee five fringes plainly, and a great num-. ber beyond, decreafing in fize and brightness till they became too small and confused for

उ

X

Optics, book iii. obf. 3.1

9

Book ii. parts & and 4.

Eight.

On the Afflions of Light.-Colours from Specula.

195

fight. In like manner, thofe formed by a double flexion of two bodies, and thofe made out of homogeneal light, were feen to a much greater number when carefully viewed through the prifin. And this experiment I alfo tried with all the fpecies of fringes by flexion which I could think of.

Obfervation 9. The fame appearances which were occafioned by the metal fpeculum, might be naturally expected to appear when a glafs one was ufed. But I alfo found the like rings or fringes of colours and spots in the image beyond the focus of a lens; nor was a very excellent one belonging to a Dollond's telescope free from them. The rings with their dark intervals refembled thofe floating fpecks fo often obferved on the furface of the eye, and called "mufcæ volitantes," only that the musce are tranfparent in the middle, because formed by drops of humor: they will, however, be found to be compaffed by rings of faint colours, which will become exceedingly vivid if the eyes be fhut and flowly opened in the fun's light, fo that the humor may be collected; they alfo appear by reflexion, mixed with the colours defcribed in Phil. Tranf. for 1796, p. 268, (or Philof. Journal I. 593.)

Obfervation 10. The fun fhining ftrongly on the concave metal fpeculum, placed at fuch a distance from the hole in the window that it was wholly covered with the light; upon inclining it a little, the image on the chart was bordered on the infide with three fringes fimilar to thofe already defcribed: on increafing the inclination these were distended, be coming very bright and beautiful: when the inclination was great, and when it was ftill increased, another set of colours emerged from the fide next the fpeculum, and was concave to that fide. Here I stopped the motion, and the image on both fides the focus had three fets of fringes, and four fringes in each fet; but when viewed through a prism (as before defcribed), the numbers greatly increased, both the fringes and the dark intervals decreasing regularly. The appearance to the naked eye is reprefented in fig. 6, plate VII. where ADC being the image, A and C are the fets of fringes at the edges, and B the third fet, there being none at E and D the fides, fince the light which illuminates thefe quarters comes not from the edges of the fpeculum in fo great inclinations. I now viewed the furface of the fpeculum, and faw it in the place answering to B in the image, covered with fringes exactly correfponding with thofe at B; and on changing the figure of that part of the fpeculum's edge between them and the fun, the fringes likewife had their figure altered in the very fame way. On moving the fpeculum farther round, B came nearer to A in the image, according as the fringes on the fpeculum receded from that fide which formed them; and before they vanished alike from the speculum and image, they mixed with the colours at A in the image, and formed in their motion a variety of new and beautiful compound colours: among thefe I particularly remarked a brown chocolate colour, and various other shades and tinges of brown and purple. Just before the fringes at B appeared, the space between A and C was filled with colours by reflexion, totally different in appearance from the fringes; but I could not examine them fo minutely as I wished in this broad image. I therefore made the following experiment:

Obfervation 11. At the hole in the window-fhut I held the fpeculum, and moved it to fuch an inclination that the colours by reflexion might be formed in the image: they were much brighter and far more diftended than the fringes, and were in every respect like the images by reflexion in the common way, only that the colours were a little better and more regular. They were alfo feen on the fpeculum, as the third fet of fringes had before Cc 2 been