COUNT RUMFOKD. 171 



coloured light. 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 4 called up,' or summoned 

 an imaginary complementary colour. Groethe probably 

 derived the expression ' geforderte Farben,' which occurs 

 so often in the ' Farbenlehre,' from the terminology of 

 Eumford. 



But the experiments and discussion on which the 

 fame of Eumford mainly rests are described in an essay 

 of twenty pages — a vanishing quantity when compared 

 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 determin- 

 ing 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 was caused to ro- 

 tate 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 rota- 

 tion, 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. 



1 Eumford carefully estimated the quantity of heat 

 possessed by each portion of his apparatus at the con- 

 clusion of his experiment, and adding all together, 

 found a total sufficient to raise 2 6' 58 lbs. of ice-cold 



12 



