serve through a strong pane of glass inserted in the side of the boiler near the liquid surface, lit up by an incandescent electric lamp within? The loss of heat by radiation from the boiler would give rise to convection-currents, and partial condensation of the vapor atmosphere; then, if the motion of the water were made visible by means of coloring matter, we should observe convection-currents in the fluid mass separate and distinct from those in the gaseous mass; but these convection-currents would cause no visible disturbance of the liquid surface, which would present itself to the eye with the smoothness of a mirror. It is only in the event of the steam-pressure being suddenly relieved at any point on the surface that a portion of the water would flash into steam, causing a violent upheaval of the liquid.
The dark spots on the sun appear to indicate commotion of this description, but these are evidently not the result of mere convection-currents; if they were, they would occur indiscriminately over the entire surface of the sun, whereas telescopic observation has revealed the fact that they do occur almost exclusively in two belts, between the equator and the polar surfaces on either side. Their occurrence could be satisfactorily explained if we could suppose the existence of strong lateral currents flowing from the polar surfaces toward the equator, which lateral currents in the solar atmosphere would cause cyclones or vortex action with a lower and denser atmosphere consisting probably of metallic vapors; this vortex action extending downward would relieve the fluid ocean locally from pressure, and give rise to explosive outbursts of enormous magnitude, projecting the lower atmosphere high above the photosphere, with a velocity measured, according to Lockyer, by a thousand miles a second. It will be seen from what follows how, according to my views, such vortex action in those intermediate regions of the sun would necessarily be produced.
But supposing that, notwithstanding the difficulties just pointed out, convection-currrents sufficed to effect a transfer of internal heat to the surface with sufficient rapidity to account for the enormous surface-loss by radiation, we should only have the poor satisfaction of knowing that the available store would last longer than might have been expected, whereas a complete solution of the problem would be furnished by a theory, according to which the radiant energy which is now supposed to be dissipated into space and irrecoverably lost to our solar system, could be arrested and brought back in another form to the sun himself, there to continue the work of solar radiation.
Some six years ago the thought occurred to me that such a solution of the solar problem might not lie beyond the bounds of possibility, and, although I can not claim intimate acquaintance with the intricacies of solar physics, I have watched its progress, and have engaged also in some physical experiments bearing upon the question, all of which have served to strengthen my confidence, and to ripen in me
