TRANSLATIONS AND SELECTED ARTICLES. 305 
the same quantity of light on an object whether the broad part or 
‘the edge of the flame is turned to it.* It follows from this that an 
‘incandescent surface of gas of a definite extent appears more lumin- 
ous when we view it obliquely than under a perpendicular incidence ; 
and consequently if the sun’s surface presents inequalities, like our 
atmosphere when it is covered with dappled clouds, it ought to ap- 
pear feebly illuminated in comparison in those portions of the in- 
equalities which are presented to the observer perpendicularly, and 
more brilliantly in the portions oblique to him. Every conical cavity 
-ought then to appear to us asaJlueule. It is not therefore necessary 
for the explanation of the appearances to suppose the existence of 
millions of points more incandescent than the rest of the disk, or of 
millions of spots distinguished from the neighbouring regions by a 
greater accumulation of luminous matiter.+ 
After having proved that the sun consists of a dark central body, 
of a cloudy reflective atmosphere, and of a photosphere,t we ought 
uaturally to ask if there is nothing beyond, and whether the photos- 
phere ends abruptly without being surrounded by a gaseous atmos- 
phere, less luminous than itself and of feeble reflective power. This 
* If 26 be the length of the jet, considered as a luminous line, and / the distance of an 
illuminated small area from the centre, the ratio of the intensities of the illumination in the 
62 62 : 
two cases will be as v§ ise a. to1l— he which if 6 be small compared with / is sensibly 1. 
{Trans.) 
+ We may add here the curious discovery of Mr. Nasmith, that the surface of the sun is 
mottled with an enormous number of lens-shaped or willow-leaved figures, disposed without 
the least attempt at symmetry. Also the fact of the decennial period of a maximum occur- 
rence of the solar spots, and iis coincidence with a corresponding maximum in the disturb- 
ance of the terrestrial magnetism due to the sun.—(Zrans.) 
{£ The recent researches of MM. Kirchoff and Bunsen, on the prismatic spectrum, which 
‘have led to the most beautiful discovery of modern times, have thrown an unexpected light 
on the question here discussed by Arago. The following brief resumé may be excused. The 
light proceeding from incandescent bodies, whether solid or liquid, gives a continuous 
spectrum when refracted through a prism, but when a fiame in which such substances are 
volatilised is examined, the spectrum,is found to be crossed by a number of bright lines of 
different colors, the number and position of such lines for each distinct substance being 
always the same. When a pure light is transmitted through such a flame, so as to over- 
power it, the bright lines become replaced by dark ones in the same positions. Now, when 
the solar beam is examined, it is found to be crossed by dark lines, which occupy the known 
places of the bright lines of various substances. It is thence inferred that the light of the 
sun proceeds from an incandescent solid or liquid body, and has passed through a vapor in 
which these substances are volatilised. Among the substances thus detected are sodium, 
lithium, iron, calcium, magnesium, chrome, nickel, cobalt, barium, copper, zinc, besides very 
many yet undetermined. Hence we are led to reject the hypothesis of Arago, (or rather of 
W. Herschel) and to adopt the more obvious supposition, that we really see the incandescent 
body of the sun through a transparent atmosphere, of considerable extent and feeble 
‘illumination, in which many known terrestrial substances exist in a state of vapor.—(T'ams.) 
Vou. VIII. x 
