48 LEADING AMERICAN MEN OF SCIENCE 



Auteuil, a suburb of Paris, where he spent the remaining five 

 years of his life in peace and quiet, dividing his time between 

 his laboratory and his garden with its fifty varieties of roses, gradu- 

 ally becoming more isolated from society, and retaining only few 

 friends, among whom were Lagrange and Cuvier. His daughter 

 Sarah joined him for a time, but was not with him when he died. 



His scientific researches in Paris were largely devoted to light, 

 and in this field his discoveries were of great importance and 

 practical value. In order to get the arithmetical results for which 

 he always strove, it was necessary to find a method of measuring 

 the relative intensity of different sources of light, and for this pur- 

 pose he invented what is known as the Rumford photometer. In 

 this the standard lamp and the one to be compared with it are so 

 placed that the two shadows cast by an opaque rod upon a screen 

 side by side are of equal intensity, then the relative brightness of 

 the lights are inversely as the squares of their distances from the 

 screen. He had an assistant move the lamps lest he should be led 

 into the temptation to distort his observations in accordance with 

 his theory. Since he found that the same weight of wax or oil 

 burned under different conditions gave off very different amounts 

 of light, he came to the conclusion that light cannot be of the 

 chemical products of combustions, but was a wave motion in the 

 ether due to the heating of solid particles in the flame. Finding 

 how small was the light compared, with what might be obtained 

 from the fuel, he experimented on wicks, air-holes, polyflame 

 burners, chimneys, etc., until he had constructed fourteen differ- 

 ent kinds of lamps. According to the Paris wits, one of these 

 gave so powerful a light that a man carrying it in the street was 

 so blinded by it that he could not find his way home, but wandered 

 in the Bois de Boulogne all night. 



He anticipated the impressionist artists in the discovery of 

 blue shadows, and, by a series of very skilful experiments, he 

 showed that whenever shadows were cast by two lights of differ- 

 ent colors, the shadows were of the complementary color, one real 

 and the other imaginary. Each color called up in the mind its 

 companion which, when combined with it, produced a pure white. 



