to mark and to make an epoch in science. Early trained in chemistry, physics, and physiology, he pursued these subjects as an investigator, not only separately, but in their intimate and complex interactions, reading the mysteries of life by the light of chemical and physical principles. From 1836, onward for fifteen years. Dr. Draper conducted a comprehensive series of researches in the general field of radiant energy in its chemical relations which had been at that time but little explored. His elaborate papers giving shape and direction to this subtile research were published in American and foreign periodicals, and won the cordial applause of his appreciative coworkers in the same fields. Recognizing that he was a good deal in advance of his time, and that years must elapse before the significance of his results would be understood, he wisely collected his papers and had them published in a quarto volume, fully and clearly illustrated. An edition of this work was printed, but the expensive stereotype plates were destroyed in the great conflagration of Harper's establishment, so that no more volumes could be produced. With the recent progress of the subjects to which it was devoted, there has been an increasing demand for copies of the work, which consequently arose in price, and were prized by all who possessed them. In these circumstances Dr. Draper has thought it best to reproduce some of the most important papers, and they are now embodied in this volume of memoirs. In this he has but done an act of justice to himself and to American science, while his volume will prove of lasting interest as a contribution to the history of a most interesting and important branch of scientific inquiry, which is now undergoing rapid development, and will continue to be zealously cultivated in the future.
As to the special subjects considered. Dr. Draper's statement of them in his preface is so much better than any we could make that it is here subjoined:
"Among many other subjects treated of in these pages, the reader will find an investigation of the temperature at which bodies become red-hot, the nature of the light they emit at different degrees, the connection between their condition as to vibration and their heat. It is shown that ignited solids yield a spectrum that is continuous, not interrupted. This has become one of the fundamental facts in astronomical spectroscopy. At the time of the publication of this Memoir, no one in America had given attention to the spectroscope, and, except Fraunhofer, few in Europe. I showed that the fixed lines might be photographed, doubled their number, and found other new ones at the red end of the spectrum. The facts thus discovered I applied in an investigation of the nature of flame and the condition of the sun's surface. I showed that under certain circumstances rays antagonize each other in their chemical effect, and that the diffraction spectrum has great advantages over the prismatic, which is necessarily distorted. I attempted to ascertain the distribution of heat in the diffraction spectrum, and pointed out that great advantages arise if wave-lengths are used in the description of photographic phenomena. I published steel engravings of that spectrum so arranged. I made an investigation of phosphorescence, and obtained phosphorescent pictures of the moon. Up to this time it had been supposed that the great natural phenomenon of the decomposition of carbonic acid by plants was accomplished by the violet rays of light, but, by performing that decomposition in the spectrum itself, I showed that it is effected by the yellow. Under very favorable circumstances, I examined the experiments said to prove that light can produce magnetism, and found that they had led to an incorrect conclusion. The first photographic portrait from the life was made by me; the process by which it was obtained is herein described. I also obtained the first photograph of the moon. I made many experiments on and discovered the true explanation of the crystallization of camphor toward the light. When Daguerre's process was published, I gave it a critical examination, and described the analogies existing between the phenomena of the chemical radiations and those of heat. For the purpose of obtaining more accurate results in these various inquiries, I invented the chlor-hydrogen photometer, and examined the modifications that chlorine undergoes in its allotropic states. Since in such researches more delicate thermometers are required than our ordinary ones, I entered on an investigation of the electro-motive power of heat, and described improved forms of electric thermometers. In these memoirs will be found a description of the method made use of for obtaining photographs of microscopic objects, together with specimens of the results. In a physiological digression respecting interstitial movements of substances, I examined the passage of gases through thin films such as soap-bubbles, and the force with which these movements are accomplished, applying the facts so gathered to an explanation of the circulation of the sap in plants, and of the blood in animals. Returning to an inquiry as to the distribution of heat and of chemical force in the spectrum, I was led to conclude, in opposition to the current opinion, that all the colored spaces are equally warm; and that, so far from one portion—the violet—being distinguished by producing chemical effects, every ray can accomplish special changes. This series of experiments on radia-
