ftill the Sun's atmosphere being manifeftly fo exceedingly full of some visible floating fluid, of fome certain denfity;-it will follow, that the extreme parts of the body of the Sun, when feen by means of any of its clofely-adhering fpots, will unavoidably appear, in con

mended, as a matter of philofophical fpeculation, to confider, that we are not without feveral inftances of terref trial bodies appearing by emitted light, even upon earth.

The Sea is often feen by emitted light;-concerning which there are fome very curious obfervations in the Philofophical Tranfactions, Vol. LIX. p. 446. 452.

The property of the Bononian, or Bolognian fione, when calcined, to imbibe fiery-red light from the Sun, and afterwards to emit it again in the dark, was known in Italy fo long ago as the year 1673;-where Mr. Ray faw the experiment. (Ray's Travels, p. 235, old edit.)

A mixture of calcined oyster-fhells with the flower of fulphur will produce the fame effect, only the light is white. (See Philof. Tranf. vol. 58, p. 337.)-Calcined belemnites will fometimes be luminous ;-and fo will fome kind of fpars after they have been a little heated; and particularly that called Island Crystal.

The glow-worm is well known and fome kind of lantern flies abroad are fo luminous, as even to afford light to read by; and their lights are differently tinted.

Whilft, to a contemplative mind, it cannot but appear moft ftriking,-that, that which is declared to be the glory of the heavens, and of heavenly Beings,-should be allowed to be manifefted, on earth, only as it were in a degraded ftate, and in the lowest order of beings.

fequence of the refractive powers of fuch an atmosphere, nearer in proportion to the margin of the Sun's apparent luminous disk, than it really is:—and that, therefore, though the real body of the Sun is probably only one third of the diameter of the Sun's apparent difk; yet that it will, by obfervations made on its spots, appear larger, juft as the bottom of a bafon filled with water, or as the bottom of a river, appears nearer to the surface of the water than it really is.

Thus in Fig. 7, let the circle (d a) reprefent the body of the Sun; and the circle (SS) the furrounding sphere of its moft intense light, or the apparent disk.

Then, to an eye placed at any diftance, as at (E); if there were no atmosphere to the Sun, a spot at (d) or at (a) would be feen by the rays, or in the line (do E) or (a o E); -and of course the whole diameter of the Sun's body would be estimated by the angle (d Ea).

But, fuppofing the intervention of an atmoSphere, of any given denfity whatever ;—and especially fuppofing it to be of any confiderable denfity, (as Sir Ifaac Newton and the most able aftronomers do conclude it to be * ;)—the

See Philof. Tranf. Vol. LVII. p. 401.

spot

fpot at (d) will be seen by a ray, or in the direction of a line, which having firft proceeded from (d) to (r), through the atmosphere, will, on paffing out of fuch denfer medium into a rarer, be bent from the perpendicular (cr p); and therefore will reach the eye in the direction (frE). And, in like manner, the spot at (a) will be seen by a ray, or in the direction of a line, which having proceeded from (a) to (t) will be bent from the perpendicular (ctq), and will reach the eye in the direction (gt E).

And confequently the diameter of the Sun's body will be eftirnated by the angle (r E t), or (f Eg);-and will appear as if it bore as great a proportion to that of the whole luminous difk, as (f g) bears to (SS):—that is, though the real diameter should be only (a d), one third of the diameter of the Sun's luminous difk,-yet it will be measured, by the eye, as if it were a great deal more:-the quantum of which enlarged appearance will be the larger, the more dense the Sun's atmosphere in reality is.

For the fake of brevity, I have explained this effect as if the whole refraction took place at the points (r) or (t):-but as we cannot but conclude that the density of the Sun's

C 4

Sun's atmosphere muft decrease gradually, from the Sun's furface, to the utmost distance that it ever reaches, (which there is reafon to believe is far beyond the limits of this luminous difk,) there will be a conftant, continually increasing refraction of every ray, the whole way, from the Sun's body, through its atmosphere; which will render the angle (r Et) or (fEg), under which the diameter of the Sun's body is estimated, fill larger.

12. And I must add;-that the fame refractive power will obviously cause the Sun's apparent luminous difk, or the furrounding fphere of intenfe light, to be itself really fomewhat nearer to its body, than the diftance here affigned, of one diameter;-becaufe of the bending of all the rays, from the extreme parts of the limb, to meet in one foint fooner, and nearer.

So that, on both these accounts, the Sun's visible diameter, or apparent disk of intense light, will indeed both be fomewhat nearer to its folid body; and will further be made to appear nearer fill, than we have firft concluded :-though, if there were no folar atmosphere, we might, on fair optical princi

ples,

ples, conclude, that it would be about three times the diameter of its body; and would alfo appear fo by obfervations on the spots.And we may even allow, that it will be caufed to appear fo much nearer to the Sun's real body, than it actually is; as to coincide perfectly, on optical principles alone, with all the obfervations, which either Dr. Herfchel or others have made, concerning fpots being at any time feen closely approaching to the edge or limb of the prefent luminous disk*: and especially if any of them, inftead of adhering quite close to the Sun's body, or being only a portion of its body become vifible, might be, in reality, at fome height in its atmosphere.

may

13. It ftill further be added;-that, consistently with the accurate mathematical reafoning of Mr. Cotes †, concerning the Earth's atmosphere, we may conclude, that the Sun's

* That most accurate obferver, the Rev. Mr. Wollaston, of Chislehurst, has seen them very near to the limb of the difk. See Philof. Tranf. Vol. LXIV. p. 337.-See allo Dr. Wilfon's reprefentations in the fame Vol. LXIV. p. 8. 12. 16.

See Cotes's Hydrostatics, p. 110 to 118; and the yery curious Paper of Bishop Horfley in the Philof. Tranf, Vol. LXIV. p. 245, &c.

atmo