I had occasion to make use of the word carbon in a lecture which I gave a short time ago, and I thought when I did so that I was of course merely using a term with whose meaning all my audience must be well acquainted. But I found out afterwards that in this matter I had been mistaken. I was told that my introduction of the word carbon had quite puzzled some of those who were listening to me. I learned that a few of those who were unfamiliar with this word went to a gentleman of their acquaintance who they thought would be likely to know, and begged from him an explanation of this mysterious term; whereupon he told them that he was not quite sure himself, but believed that carbon was something which was made out of nitro-glycerine! Even at the risk of telling what every schoolboy ought to know, I will say that carbon is one of the commonest as well as one of the most remarkable substances in nature. A lump of coke only differs from a piece of carbon by the ash which the coke leaves behind when burned. As charcoal is almost entirely carbon, so wood is largely composed of this same element. Carbon is indeed present everywhere. In various forms carbon is in the earth beneath our feet, and in the air which we breath. This substance courses with the blood through our veins; it is by carbon that the heat of the body is sustained; and the same element is intimately associated with life in every phase. Nor is the presence of carbon merely confined to this earth. We know it abounds on other bodies in space. It has been shown to be eminently characteristic of the composition of comets. Carbon is not only intimately associated with articles of daily utility, and of plenteous abundance, but with the most exquisite gems of "purest ray serene." More precious than gold, more precious than rubies, the diamond itself is no more than the same element in crystalline form. But the greatest of all the functions of carbon in the universe has yet to be mentioned. This same wonderful element has been shown to be in all probability the material which constitutes those glowing solar clouds to whose kindly radiation our very life owes its origin. [Illustration: At 10.34 A.M. The height of the eruption at this stage was 135,200 miles.] [Illustration: At 10.40 A.M. Height, 161,500 miles.] [Illustration: At 10.58 A.M. Height, 280,800 miles. THREE VIEWS OF AN ERUPTIVE PROMINENCE OF THE SUN. From photographs taken at Kenwood Observatory, Chicago, March 25, 1895, and kindly loaned by Professor George E. Hale, of the Chicago University.]