When an eclipse occurs at a spot-maximum, the distribution of the coronal features is found to have entirely changed. Instead of being sharply divided into polar brushes and equatorial wings, the streamers are distributed fairly evenly around the whole solar margin, in a manner suggesting the rays from a star, or a compass-card ornament. The existence of this periodic change has been repeatedly confirmed, and there can be no doubt that the corona reflects in its structure the system of variation which prevails upon the sun. 'The form of the corona,' says M. Deslandres, 'undergoes periodical variations, which follow the simultaneous periodical variations already ascertained for spots, faculæ, prominences, and terrestrial magnetism.' Certainty as to its composition has not yet been attained; nor is this to be wondered at, for the corona is only to be seen in the all too brief moments during which a total eclipse is central, and then only over narrow tracts of country, and all attempts to secure photographs of it at other times have hitherto failed. When examined with the spectroscope, it yields evidence that its light is derived from three sources--from the incandescence of solid or liquid particles, from reflected sunshine, and from gaseous emissions. The characteristic feature of the coronal spectrum is a bright green line belonging to an unknown element which has been named 'coronium.' The Chromosphere and the Prominences, unlike the elusive corona, may now be studied continuously by means of the spectroscope, and instruments are now made at a comparatively moderate price, which, in conjunction with a small telescope--3 inches will suffice--will enable the observer to secure most interesting and instructive views of both. The chromosphere is, to use Miss Clerke's expression, 'a solar envelope, but not a solar atmosphere.' It surrounds the whole globe of the sun to a depth of probably from 3,000 to 4,000 miles, and has been compared to an ocean of fire, but seems rather to present the appearance of a close bristling covering of flames which rise above the surface of the visible sun like the blades of grass upon a lawn. Any one of these innumerable flames may be elevated into unusual proportions in obedience to the vast and mysterious forces which are at work beneath, and then becomes a prominence. On the whole the constitution of the chromosphere is the same as that of the prominences. Professor Young has found that its normal constituents are hydrogen, helium, coronium, and calcium. But whenever there is any disturbance of its surface, the lines which indicate the presence of these substances are at once reinforced by numbers of metallic lines, indicating the presence of iron, sodium, magnesium, and other substances.