SECTION IV; CONCLUSIONS.

Solar Phenomena.

1. Sun pictures.–It appears to us probable that the varying phenomena of the sun's disc represent the play of a huge system of convection currents, the down rushes of which are indicated by the darker patches and up rushes by the brighter patches. These currents appear to be always present on the sun's surface, and to give rise to the mottled appearance which it presents under high magnifying powers. It would seem, however, that the scale of these phenomena, and the rapidity of the indicated motions, are on certain occasions greatly increased, presenting to the observer that complex appearance which is associated with the outbreak of spots. Thus sun spots may be supposed to denote gigantic down currents of comparatively cold matter from above, while the faculæ and red flames may denote the corresponding up rush of hot matter from beneath.

We are also of opinion that it is in virtue of this convection system that our luminary is able to bring to the surface the intensely heated matter requisite to supply the enormous quantity of radiant energy which it is known continuously to give out. It would seem to follow that when this convection system is peculiarly vigorous the radiation from the sun's disc must be peculiarly vigorous also. Now all observations tend to convince us that the sun's atmosphere is most agitated at epochs of maximum sun spot frequency, and perhaps we may likewise conclude from Mr Lockyer's investigations that certain definite levels present the spectral characteristics of a peculiarly high temperature at such times.