astronomy. 
eerning the nature-of the foul : Hamm Jcntcntiarum qua: 
no a Ju, Dens aliquis vidcrit ; qua: verifimillima magna quej^io 
eji Watfon’s Chem. E(T. vol.i. p.164. 
Although the furface of the Sun appears to human 
eyes Ip extremely bright and fplendid, we neverthelefs 
find a number of dark (pots of different kinds moving upon 
it. Thefe were entirely unknown before the invention of 
telefcopes, though they are fometimes of fufficient mag¬ 
nitude to be difcerned by the naked eye. The (pots are 
fa id to have been firft obferved in the year 1611 ; and the 
honour of the difcovery is difputed betwixt Galileo and 
Scheiner, a German jefuit at Ingolftadt. There is great 
variety in the magnitudes of the (pots ; fame have been 
fo large, as by computation to be capable of covering the 
continents of Ada and Africa ; nay, the whole furface of 
the earth, or even five times its (urface. The diameter 
of a (pot, when near the middle of a difk, is meafured 
by comparing the time it takes in pafftng- over a crofs hair 
in a telelcope, with the time wherein the whole diflc of 
the Sun p.affes over the fame hair; it may alfo be meafured 
by the micrometer; and by either of thefe methods we may 
judge how many times the diameter of the fpot is contained 
in the diameter of the Sun. Spots are fubjeft to an in- 
ereafe and diminution of magnitude, and feldom continue 
long in the fame (late. They are of various lhapes ; mod 
of them having a deep black nucleus furrotinded by a 
dulky cloud, whereof the inner parts are a little brighte/- 
than the outer. They change their fliapes, fomething in 
the manner that clouds do; though not fo fuddenly : thus, 
what is of a certain figure to-day, (hall, to-morrow, or in 
a few hours, be of a different one ; w hat is now but one 
fpot, (hall in a little time be broken into two or three ; 
and fometimes two or three fpots (hall coalefce, and be 
united into one. Dr. Long, while he was viewing the 
image of the Sun through a telefcope cad upon white paper, 
favv oneroundifii fpot, by edimation not much lefs than the 
diameter of our Earth, break into two, which receded from 
one another with prodigious velocity. This obfervation was 
Singular at the time ; for, though feveral writers had taken 
notice of this after it was done, none of them had been 
making any obfervation at the time it was actually doing. 
The number of fpots on the Sun is very uncertain ; 
fometimes there are a great many, fometimes very few, 
and fometimes none at all. Scheiner made obfervations on 
the Sun from 1611 to 1629 ; and fays he never found the 
di(k quite free of fpots, excepting a few days in Decem¬ 
ber 1624. At other times he frequently faw twenty or 
thirty, and in the year 1625 he was able to count fifty 
fpots on the Sun at a time. In an interval afterwards of 
twenty years, from 1650 to 1670, fcarcely any fpots were 
to be feen, and fince that time fome years have furnidied 
a great number of fpots, and others none at all ; but, fince 
the beginning of the lad century, not a year paffed wherein 
fome were not feen; and at prefent, fays M. Caffmi, in 
his Elemens-d ’ AJlronomi-e, they are fo frequent, that the Sun 
is feldom without fpots, and often (hews a great number 
of them at a time. 
From thefe phenomena, it is evident, that the fpots are 
not endowed with any permanency, nor are they at all re¬ 
gular in their (hape, magnitude, number, or in the time 
of their appearance or continuance. They all appear to 
have a motion which carries them acrofs the Sun’s di(k. 
Every fpot, if it continues long enough without being dif- 
folved, appears to enter the Sun’s difk on the ead fide, to 
go from thence with the velocity continually increafing till 
it has gone half its way ; and then to move (lower and 
flower, till it gees off at tile wed fide ; after which it dis¬ 
appears for the fame fpace of time that it fpent in eroding 
the difk, and then enters upon the ead fide again, nearly 
in the fame place, and erodes it in the fame track, and with 
the fame unequal motion as before. This apparent ine¬ 
quality in the motion of the fpots is purely optical, and is 
in fiich proportion as demonflrates them to be carried round 
equably or in a circle, the plane of which continued paffes 
through ox near the eye of a fp.eftator upon the Earth. 
The nature and formation of the folar fpots have been the 
fubjeff of much (peculation and conjecture. Schemer 
fuppofed them to be folid bodies revolving about the Sun, 
very near to it; but, as they are as long vifible as invifible, 
this cannot be the cafe. Moreover, we have a phyfical argu¬ 
ment againd this hypothefis, w hich is, that mod of them do 
not revoiveabout the Sun in a plane pading through its cen¬ 
tre, which they neceffarily mud, if they revolved like the 
planets about the Sun. Galileo confuted Scheiner’s opi¬ 
nion, by obferving that the fpots were not permanent; 
that they varied their figure; that they irxreafed and de- 
creafed, and fometimes difappeared. He compared them 
to fmoke and clouds. Hevelius appears to have been of 
the fame opinion; for in his Cometographia, p. 360, fpeak- 
ingof the folar fpots, he fays, “ haec materia nunc ea ipfa 
ed evaporatio et exhalatio (quia aliunde mini me oriri po- 
ted) quae ex ipfo corpore fobs, ut fupra odenfum ed, ex- 
piratur et exhalatur.” But the permanency of mod of 
the fpots is an argument againd this hypothefis. M. de 
la Hire fuppofed them to be folid opaque bodies, which 
fvvim upon the liquid matter of the Sun, and which are 
fometimes entirely immerfed. M. de la Lande fuppofed 
that the Sun is an opaque body, covered with a liquid fire, 
and that the fpots arife from the opaque parts, like rocks, 
which, by the alternate flux and reflux of the liquid ig¬ 
neous matter of the Sun, are fometimes raifed above the 
furface. The fpots are frequently dark in the middle, 
with an umbra about them ; and M. de la Lande fuppofes 
that that part of the rock which flands above the furface 
forms the dark part in the centre, and thofe parts which 
are but juft covered by the igneous matter form the um¬ 
bra. Dr. Wilfon, profefforof allronomy at Glafgow, op- 
pofes this hypothefis of M. de la Lande, by this argument: 
generally fpeaking, the umbra immediately contiguous to 
the dark central part, or nucleus, infiead of being very 
dark, as it ought to be, from our feeing the immerfed 
parts of the opaque rock through a thin firatum of the 
igneous matter, is, on the contrary, very nearly of the 
fame fplendour as the external furface, and the umbra 
grows darker the further it recedes from the nucleus ; 
this, it muft be acknowledged, is a flrong argument again!! 
the hypothefis of M. de la Lande. Dr. Wilfon further 
obferves, that M. de la Lande produces no optical argu¬ 
ments in fupport of the rock (landing above the furface of 
the Sun. The opinion of Dr. Wilfon is, that the fpots 
are excavations in the luminous matter of the Sun, the 
bottom of which forms the umbra. Befides the dark fpots 
upon the Sun, there are alfo parts of the Sun, called facu~ 
la, luculi , &c. which are brighter than the general furface ; 
thefe always abound mod in the neighbourhood of the 
fpots themfelves, or where fpots recently have been. Mod 
of the fpots appear within the compafs of a zone lying' 
30 0 on each fide of the equator; but on July 5, 1780, M. 
de la Lande obferved a (pot 40° from the equator. 
The lateft obfervations on the folar fpots, and on the 
nature and conftruftion of the Sun, are thofe of Dr. Herf- 
chel, publifhed in the Philofophical Tranfadlions of 1795. 
He fays, “ There was a fpot on the Sun in the year 1779,, 
which was large enough to be feen with the naked eye. 
By a view of it with a 7-feet refleftor, charged with a 
very high power, it appeared to be divided into two parts. 
The largefl; of the two, on the 19th of April, meafured 
1' 8"-o6 in diameter; which is equal in length to more - 
than thirty-one thoufand miles. Both together mu ft cer¬ 
tainly have extended above fifty thoufand ! The idea of 
its being occafioned by a volcanic explofion, violently driv¬ 
ing away a fiery fluid, which on its return would gradually 
fill up the vacancy, and thus reftore the Sun in that place 
to its former fplendour, ought to be rejedled on many ac¬ 
counts. To mention only one, the great extent of the 
lpot is very unfavourable to that fuppofition. Indeed a 
much lefs violent and lefs pernicious caufe may be affigned, 
to account for all the appearances of the fpot. When we 
fee a dark belt near the equator of the planet Jupiter, we 
do not recur to earthquakes and volcanoes for its origin. 
An 
