1883.] on Count Rumford, Originator of the Royal Institution. 453 



nary. He finds it " impossible to produce two shadows at the same 

 time from the same body, the cue answering to a beam of daylight, 

 and the other to the light of a caudle or lamp, without these shadows 

 being coloured, the one yellow, and the other blue." He obtained 

 shadows from a light coloured by means of interposed glasses, 

 and compared them with shadows obtained from uncoloured lifrht'. 

 The shadows were always coloured when the lights differed from 

 each other in whiteness, and the colours of the shadows were 

 always such as, when added together, produced a pure white. The 

 real colour in fact, evoked, or " called up," or summoned an imagi- 

 nary complementary colour. Goethe probably derived the expression 

 " geforderte Farben," which occurs so often in the " Farbenlehre " 

 from the terminology of Rumford. 



But the experiments and discussion on which the fame of Rumford 

 mainly rest are described in an essay of twenty pages, which almost 

 vanishes in comparison with the sum total of his published work. 

 A cannon foundry had been built under his superintendence at 

 Munich, where the heat developed during the boring of cannon 

 powerfully attracted his attention. Upon this heat he made numerous 

 tentative experiments which are described in the essay. With 

 the view of determining its exact quantity, he cut a cylinder from 

 the muzzle end of a gun not yet bored, partially hollowed out 

 this cylinder, and fitted into it a borer which resembled a blunt 

 chisel in shape. The borer being strongly pressed against the 

 bottom of the cylinder, it w^as caused to rotate by horse-power. He 

 surrounded his cylinder with a wooden box, filling the box with water 

 which embraced the entire cylinder. Soon after the starting of the 

 rotation, the water felt warm to the hand. In an hour it had risen to 

 107° in temperature. In two hours and twenty minutes it had risen 

 to 200°, while in two hours and thirty minutes it actually boiled. 



" Rumford carefully estimated the quantity of heat j^ossessed by 

 each portion of his aj)paratus at the conclusion of his experiment, and 

 adding all together, found a total sufficient to raise 26*58 lbs. of ice- 

 cold water to its boiling-point, or through 180° Fahr. By careful 

 calculation he found this heat equal to that given out by the com- 

 bustion of 2303 • 8 grains ( = 4y q oz. troy) of wax. He then deter- 

 mined the ' celerity ' with which the heat was generated, summing 

 up thus : ' From the results of these computations it appears that 

 the quantity of heat produced equably, or in a continuous stream, if 

 I may use the exjDression, by the friction of the blunt steel borer 

 against the bottom of the hollow metallic cylinder, was greater than 

 that produced in the combustion of nine wax candles, each three- 

 quarters of an inch in diameter, all burning together with clear 

 bright flames.' 



" ' One horse,' he continues, ' would have been equal to the work 

 performed, though two were actually employed. Heat may thus be 

 produced merely by the strength of a horse, and, in a case of neces- 

 sity, this heat might be used in cooking victuals. But no circumstances 



