700 Scientific Proceedings, Royal Dublin Society. 
of transfer of heat will depend on how nearly the region beneath 
and around the spot approximates to the temperature of the liquid. 
On these views we may infer that the present temporary nature 
of such developments of liquid matter upon the surface of the sun 
will in the future gradually disappear. In the present stage of 
cooling, the diminution of temperature due to loss by radiation 
over the Solar Spot soon leads to equalisation from within: to a 
rise in the isothermals and re-evaporation of the liquid. But this 
will not be so in the remote future. Gradually the internal sup- 
plies will diminish and the rate of equalisation will decrease. Spots 
will be of larger extent and of longer duration, till ultimately the 
present (probable) state of the Earth is attained, a liquid or viscous 
mass coated with a solid crust, and agitated with gradually declin- 
ing volcanic outbreaks. The duration of solar energy as a sus- 
tainer of life upon the Harth will probably be limited by the advance 
of the change of state. When the emissivity of the Sun is thus 
reduced, his rate of shrinkage and consequent dynamical evolution 
of heat will correspondingly diminish ; and while his final cooling 
will be the longer postponed, his radiated energy will be no longer 
available as a source of life upon his satellites. 
It is perhaps not improbable that many irregularly variable 
stars are in a stage more advanced than the present stage of 
our Sun. They may constitute in fact an extreme demonstration 
of the flicker observed in the tube in which matter fluctuates 
between the liquid and gaseous states. It is not impossible that 
our problematical Glacial Epoch may be referred to a Sun-Spot 
period, due to the change of state of some constituent now finally 
transferred deeper into the gaseous solar envelopes, or to the 
present gaseous elements condensed and re-evaporated on an 
exaggerated Sun-Spot period, the cause of which is, however, 
not assignable. 
It isnow many years since I heard Dr. G. J. Stoney suggest that 
a liquid substratum to the photosphere and rents in the latter 
would explain the appearance of the Sun-Spot. He pointed 
out that the liquid within would reflect the dark sky, and appear 
as a less luminous area than the surrounding photosphere. The 
foregoing speculations obviously involve, in many respects, similar 
conditions. 
