J. R. Mayer on Celestial Dynamics. 193 
the same weight of coal; just as small as is the amount of heat 
developed by a weight moving with the not inconsiderable 
velocity of 85 metres in one second. But, according to the laws 
of mechanics, the effect-is proportional to the square of velocity; 
if, therefore, the weight move 100 times faster, or with a velocity 
of 8500 metres in one second, it will produce a greater effect 
than the combustion of an equal quantity of coal. 
It is true that so great a velocity cannot be obtained by human 
means; everyday experience, however, shows the development 
of high degrees of temperature by mechanical processes. 
In the common flint and steel, the particles of steel which are 
struck off are sufficiently heated to burn in air. A few blows 
directed by a skillful blacksmith with a sledge-hammer against 
a piece of cold metal may raise the temperature of the metal at 
the points of collision to redness. ae 
The new crank of a steamer, whilst being polished by friction, 
becomes red-hot, several buckets of water being required to cool 
it down to its ordinary temperature. ; 
When a railroad train passes with even less than its ordinary 
One of the grandest constructions for the production of motion 
by human art is the channel in which the wood was allowed to 
gli 
Ce ee 
Rays of heat on passing through glass and other transparent 
bodies undergo partial ainonek which differs in degree, how- 
ever, according to the temperature of the source from which the 
i i warm than 
of 
glass. As the temperature of a source of heat increases, its 
