698 Scientific Proceedings, Royal Dublin Society. 
What the conditions regarding the convective transfer of heat 
in the deeper layers are we do not with certainty know. The 
general tendency of pressure to confer solidity may, however, with 
probability be supposed to confer even at solar temperatures a 
certain degree of viscosity. In any case, the increased density 
means increased inertia per unit volume, and therefore involves a 
less disturbed state of things than is manifest upon the surface. 
The intense radiation of the Sun is, on these views, mainly the 
radiation of matter above the critical temperature. His continuous 
spectrum is derived from this radiation. Sir Norman Lockyer has 
shown that such a continuous spectrum is quite in harmony with 
a gaseous state. : 
Proceeding outwards in the photosphere a fall in temperature 
must be supposed to occur. Convective carriage of heat cannot 
avert this, for any such rise of gaseous matter must be accompanied 
by dynamical cooling. Finally, a temperature will be reached at 
which the critical temperature of the mixed elemental gases of that 
region, or of some one predominant constituent element, say carbon, 
is attained. When this is reached in a region where the pressure 
is at, or above, the critical pressure, a rain of matter in the liquid 
state will occur; such a rain as Amagat observed in his tube of 
carbon dioxide near the critical temperature of the gas. 
That the estimated photospheric temperature of 8000° C. 
“may approximate to the critical temperatures of many of the 
elements is not improbable when it is considered how high in the 
scale of temperature even the melting points of many of the metallic 
elements stand. The melting point of carbon is unknown, and, as 
appears from the experiments of Mr. Wilson and Professor Fitz- 
Gerald, is probably above that of the electric are: 33800-8500° C. 
On these considerations a theory of Sun-Spots is suggested. 
The Sun-Spot is, in fact, a flood or layer of liquefied matter floating 
upon the denser gaseous matter beneath. It constitutes the first 
approach to a change of state in the Sun visible tous. At the 
level of the spot a cooling has been temporarily produced ; possibly 
due to radiation through parted photospheric gases (and the 
Sun-Spot is often preceded by more intense local brightness), 
possibly by sudden expansion attending up-rush from within, 
the final result being a fall in temperature sufficient to permit 
