In particular, it has always seemed to me that the curved, especially the doubly curved, streamers of the corona can only be well explained by regarding the corona as in the main an auroral phenomenon. If mighty currents prevailed in the higher regions of a rare atmosphere, extending hundreds of thousands of miles from the sun's surface, appearances such as these curved streamers would undoubtedly be explained. But no one who considers the effect of the sun's tremendous attractive power on such an atmosphere can fail to perceive that, according to the known laws connecting gaseous pressure and density, the density of that atmosphere would be enormously great, even at a very great distance from the sun's surface, if the curved streamers really were caused by atmospheric currents. We know, on the contrary, from the behaviour of comets which have passed very near to the sun, that the atmosphere above his visible surface must be very rare indeed. It must not be understood, however, that I regard the corona as simply a great solar aurora. It is certain that the whole region filled by the corona is occupied by immense numbers of scattered meteors, and extremely probable that large quantities of cometic matter exist within the same region. Vaporous masses may also be there, circling independently around the sun. But that this region is illuminated constantly by auroral light, varying greatly in intensity and position, seems very strongly indicated by all that we know about the corona, as seen during different total eclipses of the sun. If we so viewed the solar corona, and found our earth, therefore, in this respect resembling the great central orb of the solar system, we could not but regard as extremely probable the theory that other planets also resemble the central body in this respect. We might then picture to ourselves every orb in the solar system carrying onward its faintly luminous crowns of boreal and austral light, not shining with constant lustre, or in the same constant position, but at one time leaping in coloured steamers to a great distance from the body they adorned, and anon sinking down and growing fainter and fainter, or occasionally disappearing altogether. Then, when some great disturbance affected the central sun, and caused _his_ auroral banners to shine out more brilliantly and to attain a greater extension, suddenly the auroral streamers of all the planets would leap out into new light and life, playing around the northern and southern magnetic poles of those orbs, even as electric brushes play around the positive and negative electrodes of a Geissler's tube. "Suddenly" at least so far as each planet is concerned, but not suddenly throughout the whole system. For the magnetic influences, like the light and heat of the sun, require time for their transmission. Yet, so rapidly do they travel that, in a few hours, the auroral illumination would extend from the central sun to the outermost limits of his system.