JOHN WILLIAM DRAPER. 



the source of the fixed lines of the bright spectrum, and he observed 

 that new lines are developed as the temperature rises. " Do not the 

 various facts here brought forward," he says, "prove that chemical 

 combinations are attended by a rapid vibratory motion of the par- 

 ticles of the combining bodies, which vibrations become more fre- 

 quent as the chemical action is more intense ? " This memoir may 

 be regarded as one of the earliest contributions to spectrum analysis. 



In a subsequent memoir, written in 1857, Dr. Draper uses the fol- 

 lowing remarkable language : " In other cases dark lines are replaced 

 by bright ones, as in the well-known instance of the electric spark 

 between metallic electrodes. The occurrence of lines, whether bright 

 or dark, is hence connected with the chemical nature of the substance 

 producing the flame. For this reason these lines merit a much more 

 critical examination, for by their aid we may be able to ascertain 

 points of great interest in other departments of science. Thus, if 

 we are ever able to acquire certain knowledge respecting the physi- 

 cal state of the sun and other stars, it will be by an examination of 

 the light they emit." Surely these researches, with the prophetic 

 conclusions which he drew from them, entitle Professor Draper to a 

 recognized position among the pioneers in the science of prismatic 

 analysis. 



Some of the earliest of Dr. Draper's investigations were directed 

 to a determination of the various forms of energy which exist in 

 solar light. The chemical action of light was always a fascinating 

 subject to him and he had made many interesting experiments to 

 ascertain the effect of different kinds of light upon chemical change. 

 These chemical actions were investigated in three different direc- 

 tions. The first of these was photography. For many years he 

 had studied the action of light in changing the color of metallic 

 salts, and he had already long been accustomed to apply the photo- 

 graphic process to the solution of physical problems when Daguerre's 

 discovery was announced in 1839. He welcomed the daguerreotype 

 enthusiastically, made a special study of it, and in the same year 

 improved it so much that he took by its means the first portrait of 

 the human face. In these days of rapid emulsion processes the 

 directions he gives for taking a daguerreotype appear interesting. 

 " In the first experiments I made," he says, " the face of the sitter 

 was dusted with a white powder, but a few trials showed that this 

 was unnecessary." "On a bright day and with a sensitive plate por- 

 traits can be obtained in the course of five or seven minutes in the 



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