348 M. F. Zollner on the Temperature and 



in the atmosphere of elastic fluid above them currents analogous 

 to the land- and sea-breezes on our earth as, according to expe- 

 rience, established by difference of temperature between land and 

 water on the coasts of the islands. Therefore, along the coast 

 of a scoria island on the surface of the sun, winds must be evolved, 

 which in general are directed perpendicular to the coast ; but 

 these currents will, in the lower parts of the atmosphere, be di- 

 rected outward from the interior of the island — in the upper, 

 i. e. in the parts turned towards and visible to us, from without 

 to the interior. There must thus arise at the borders of a mass 

 of scoria whirlwinds, the axis of rotation of which follows hori- 

 zontally its contour and is determined by it. 



" In the parts of the atmosphere above the scoria, on account 

 of the less radiation, products of condensation must of necessity 

 be formed, which, cloudlike in their nature, will have their con- 

 sistence and shape determined in great measure by the atmo- 

 spheric currents which are directed to the centre. If now the 

 vapours have attained the elasticity corresponding to the lower 

 temperature over the scoria (which will obviously be more and 

 more nearly the case as the moving portions of the atmosphere 

 approach the centre of the island), the cause of cloudiness ceases, 

 and we behold through the lightened and torn veil of cloud the 

 underlying island of scoria as the nucleus of a spot. 



"The boundaries of this island are therefore, according to the 

 theory, still concealed by the penumbrse — which are the cloud- 

 like products of cooling in the sun's atmosphere above a scoria- 

 mass, becoming visible to us. According to this, the portions 

 of the atmosphere over the nucleus of a spot must be regarded 

 as filled with vapours the elasticity of which corresponds to the 

 lower temperature over the scoria island. Hereby, taking also 

 into consideration the experiment described in the last Part*, 

 the widening of the dark lines of the spectrum where they inter- 



* This is the experiment described by Kirchhoff in the year 1860 (Pogg. 

 Ann. vol. cix. p. 297), by which it is shown that the insignificant quantity 

 of incandescent sodium vapour in the mantle of an alcohol-flame can, by 

 virtue of its low temperature, widen and darken the sodium-lines in the 

 solar spectrum when the solar rays are caused to pass through those 

 flames. On this Kirchhoff remarks, " There is at the first in&tant some- 

 thing surprising in the fact that the sodium in the little flame can percep- 

 tibly reinforce the action exerted upon the rays of light by the sodium in 

 the immense atmosphere of the sun. But the surprise vanishes when we 

 consider that the brightness of the lines D in the solar spectrum is deter- 

 mined by the temperature of the sun's atmosphere, preeminently of its 

 outer layers, and that the temperature of these is certainly very much 

 higher than that of a gas-flame." We see from this that the widening and 

 darkening of some metal-lines in the spectrum of the sun-spots must not 

 be regarded as an evidence of the greater quantity of absorbing vapours in 

 those parts, but, primarily, only of the existence of a lower temperature of 



