114 



THE POPULAR SCIENCE MONTHLY, 



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 re- 

 searches in the general field of radiant en- 

 ergy 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 co- 

 workers 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 under- 

 stood, 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 stereo- 

 type plates were destroyed in the great con- 

 flagration 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 increas- 

 ing demand for copies of the work, which 

 consequently arose in price, and were prixed 

 by all who possessed them. In these circum- 

 stances Dr. Draper has thought it best to re- 

 produce 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 last- 

 ing interest as a contribution to the history 

 of a most interesting and important branch 

 of scientific inquiry, which is now under- 

 going 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 pref- 

 ace is so much better than any we could 

 make that it is here subjoined: 



"Amons many other eubjecte treated of in 

 these pages, the reader will find an investiga- 

 tion of the temperature at which bodies become 

 red-hot, the nature of the light they emit at dif- 

 ferent 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 be- 

 come one of the fundamental facts in astronomi- 



cal spectroscopy. At the time of the publica- 

 tion 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 f;icts thus discov- 

 ered I applied in an investigation of the nature 

 of flame and the condition of the snn's surface. 

 I showed that under certain circumstances rays 

 antagonize each other in their chemical effect, 

 and that the diffraction spectrum has great ad- 

 vantages over the prismatic, which is necessari- 

 ly distorted. I attempted to ascertain the dis- 

 tribution 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 experi- 

 ments said to prove that light can produce mag- 

 netism, and found that they had led to an incor- 

 rect 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 ex- 

 amination, and described the analogies existing 

 between the phenomena of the chemical radia- 

 tions and those of heat. For the purpose of 

 obtaining more accurate results in these various 

 inquiries, I invented the chlor-hydrogen pho- 

 tometer, 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 elec- 

 tric thermometers. In these memoirs will be 

 found a description of the method made use of 

 for obtaining photographs of microscopic ob- 

 jects, together with specimens of the results 

 In a physiological digression respecting inter- 

 stitial 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 chem- 

 ical effects, every ray can accomplish special 

 changes. This series of experiments on radia 



