BENJAMIN THOMPSON, COUNT RUMFORD 49 



He calls attention to the value of such studies for artists, house 

 furnishers and " ladies choosing ribbons," and suggests enter- 

 tainments of color harmonies, like musical concerts. Rumford 

 also experimented on the chemical effects produced by light, such 

 as the deposition of a film of metallic gold and silver on a ribbon 

 or slip of ivory which had been dipped in a solution of their salts; 

 a reaction which forms the basis of modern photography. 



His researches on heat and light were based upon determina- 

 tions of the heat of combustion of the fuel used by means of an 

 ingeniously devised calorimeter. In this the products of com- 

 bustion are drawn through a worm immersed in a known quantity 

 of water and the increase in the temperature of the water deter- 

 mined by a thermometer immersed in it. By having the water 

 at the beginning of the experiment about as much cooler than the 

 room as it was warmer at the end, one of the chief sources of error, 

 that of loss of heat to the air, was practically eliminated: a method 

 still in use. With this apparatus, which has only recently been 

 superseded by the bomb calorimeter using compressed oxygen, 

 he determined with remarkable accuracy the heat of burning alco- 

 hol, hydrogen, carbon and many kinds of wood, coal, oil and wax. 

 From a determination of the heat of combustion of wood and of 

 charcoal made from it, he deduced the fact that the gas lost in 

 making charcoal is the most valuable part of the fuel. 



In looking over Count Rumford's papers after a hundred years 

 of scientific work has been done in the fields where he was a 

 pioneer, one is forcibly struck by his selection of what were the 

 most important problems to be solved. This is shown, for ex- 

 ample, in the interest he took in the inconspicuous phenomena 

 of surface tension, and his study of the pellicle covering the sur- 

 face of water, which supports a globule of mercury as in a pocket, 

 and gives footing to water-spiders. He clearly shows the impor- 

 tance of this in movements of sap in the trees and of the fluids of 

 the animals; a line of investigation that just now is proving ex- 

 tremely fruitful in physics and physiology. 



While in Paris he experimented on the proper construction of 

 wagon wheels, and invented a dynamometer by which the pull of 



