Humboldt is an illustration of what a man is worth intellectually after he is sixty or seventy. It is true that he did some great things before he was sixty, but his greatest works were produced after that period. He was sixty years old when, at the instance of Emperor Nicholas of Russia, he undertook a scientific expedition to the north of Asia to explore the Ural and Altai Mountains, Chinese Dzungaria, and the Caspian Sea. He was sixty-seven when he published, in five volumes, a Critical Examination of the Geography of the New Continent. When about seventy-four years old, Humboldt began to compose Cosmos: Essay of a Physical Description of the Universe, which has been unanimously recognized as "one of the greatest scientific works ever published." The fourth and last volume was not issued until 1858, one year before his death at the age of ninety.

A writer who made a reputation for himself as an author late in life, was Saavedra Cervantes. The first part of Don Quixote, which Carlyle calls "our joy fullest modern book," was published when he was nearly sixty, and eight years passed before the second part ap peared. Cervantes and Shakespeare died on the same day, April 23, 1616.

It is refreshing to read how Goethe wrought at his tasks till he passed the age of eighty. Time did not seem to weaken his intellect nor slacken his energy. In its literary phases, his life may be divided into four periods, the fourth being that of old age - from 1805, when he was fifty-six, to the year of his death, at the age of eighty-three. During that period a large number of works were published - some of his greatest - and among them is Faust, his masterpiece. The first part was written when Goethe was between fifty-six and fifty-eight, and the second part was completed only a few months before his death in 1832. Some of his most beautiful poems were written when he was about seventy-five.

It was late in life that Victor Hugo began some of his great works. Les Miserables was written when he had passed fifty-seven, and was published in ten languages on the same day in 1862. The Toilers of the Sea was brought out when he was sixty-four, and The Annals of a Terrible Year, at seventy, at which age his mental vigor showed no sign of decline. Hugo's Ninety-Three, published when he was about seventy-two, is regarded by wise and able critics to be the most virile of his novels, with "more intensity of action and a truer tragic catastrophe" than even Les Miserables. The last part of The Legends of the Centuries, written when he was approaching eighty, reaches the high-water mark of his achievement in lyrical epic.

A striking example of how mental activity can be maintained during the period commonly called old age, is found in the life of Mrs. Mary Somerville, the distinguished English mathematician and scientist. She did not allow herself to suffer from brain rust, nor to become irritable from dyspepsia or gloomy thoughts. She was fifty years old when the first of her important works, Celestial Mechanism of the Heavens, was brought out in London in 1830. At fifty-five, Mrs. Somerville prepared The Connection of the Physical Sciences; at sixty-eight, Physical Geography; at eighty-six, Molecular and Microscopic Science.

At the age of ninety-two Mrs. Somerville wrote: "I am still able to read books on higher algebra for four or five hours in the forenoon"; and to the day of her death at Naples, in 1872, she was engaged on the revision and completion of a treatise on The Theory of Differences, which included some exquisite drawings. Only a few days before she passed away, she said: "I regret that I shall not live to learn the result of the expedition to determine the currents of the ocean, the distance of the earth from the sun determined by the transit of Venus, and the source of the most renowned river."

No physician in this country, excepting Oliver Wendell Holmes, has written so many volumes on varied topics as Dr. Silas Weir Mitchell of Philadelphia. In the practice of his profession he is eminent and always busy, and yet he has found time to do a large amount of literary work. He is seventy-five years old, but in his medical practice and in his literary labors he is still actively engaged. I make this reference to Dr. Mitchell because his best literary efforts have been accomplished since he reached the age of fifty. He has written something like thirty volumes, besides one hundred and twenty-five essays and monographs upon nervous diseases, poisons and their antidotes, comparative physiology, and chemical medicine. His Hugh Wynne, generally conceded to rank among the best stories of the American Revolution, was written when the doctor was nearly sixty-six years old. His clever Comedy of Conscience, was published two years ago; and a book that will appeal to every patriotic Amer ican boy is Dr. Mitchell's The Youth of Washington, which is skilfully written in an autobiographic form. It was little less than a marvellous undertaking in a man who has devoted his long life to medicine and scientific pursuits. But his new novel, Constance Trescot, is regarded by critics to be the greatest of all his works. It is a powerful psychological study of a woman, is intensely interesting, and was written when the doctor was seventy-five.

The list of names prominently associated with the subject of "Age in Relation to Mental Activity" is a long one and interesting. Time and again has it been proven that the highest level of courage, insight, and faith, has been reached by men and women after they have passed three-score years and ten.