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Rh necessary for the preparation of his work, and to furnish him with statistical information respecting the armies of the United States, their organization, and operations." This order included all the Confederate archives in possession of the War Department. Nor was the interest of the Secretary of War limited to this: he supplied also a large amount of personal information of the utmost value. Access was not unfrequently given him to documents and correspondence of the most confidential kind, with a view of guiding him to correct conclusions, and many of the most decisive military operations are detailed from private memoranda furnished by the commanding officers themselves. As was the case with Dr. Draper's other works, this also has been largely republished in Europe.

In the summer of 1870 Dr. Draper suffered a severe bereavement in the loss of his wife. Of Brazilian birth, she was connected with an ancient and noble Portuguese family. She had rendered his domestic life a course of unbroken happiness, and doubtless she was the exemplar before his eyes when he wrote that often-quoted passage in his "Physiology," in which, after depicting the physical and intellectual peculiarities of woman, he says: "But it is in the family and social relations that her beautiful qualities shine forth. At the close of a long life checkered with pleasures and misfortunes, how often does the aged man with emotion confess that, though all the ephemeral acquaintances and attachments of his career have ended in disappointment and alienation, the wife of his youth is still his friend. In a world from which every thing else seems to be passing away, her affection alone is unchanged, true to him in sickness as in health, in adversity as in prosperity, true to the hour of death."

Of their six children, one died in infancy; the survivors are three sons and two daughters. Of the former, the eldest is Professor of Natural History in the College of the City of New York; the second, Professor of Physiology in the University of New York; the third, Director of the Meteorological Observatory in the New York Central Park.

After the death of his wife, Dr. Draper spent the following winter in Europe, chiefly in Rome. Since his return he has published two short memoirs: one, on the "Distribution of Heat in the Spectrum," showing that the predominance of heat in the less refrangible regions is due to the action of the prism, and would not be observed in a normal spectrum, such as is formed by a grating; and that all the rays of light have intrinsically equal heating power. The second is an investigation of the distribution of chemical force in the spectrum. All these scientific researches, to which so many years of his life have been devoted, have been at his own expense; he has never received any extraneous aid, though many of them have been very costly. He has never taken out any patent, but has given the fruits of his investigations and inventions freely to the public.