376 MEETING OF BRITISH ASSOCIATION. 



less, receive much attention from the association at their present 

 meeting. To persons who contend that all geological phenomena 

 may be attributed to causes identical in nature and degree with 

 those now in operation, the formation of coal must present peculiar 

 difficulty. The rankness of vegetation which must have existed 

 in the carboniferous era, and the uniformity of climate which 

 appears to have prevailed almost from the poles to the equator, 

 would seem to imply a higher temperature of the earth's crust, 

 and an atmosphere more laden with humidity and carbonic acid 

 than exist in our day. But, whatever may have been the geologi- 

 cal conditions affecting the origin of coal, we may regard the de- 

 posits of that mineral as vast magazines of power stored up at 

 periods immeasurably distant for our use. The principle of con- 

 servation of force and the relationship now established between 

 heat and motion enable us to trace back the effects which we now 

 derive from coal to equivalent agencies exercised at the periods of 

 its formation. The philosophical mind of George Stevenson, 

 unaided by theoretical knowledge, rightly saw that coal was the 

 embodiment of power originally derived from the sun. That small 

 pencil of solar radiation which is arrested by our planet, and which 

 constitutes less than the 2,000-millionth part of the total energy 

 sent forth from the sun, must be regarded as the power which 

 enabled the plants of the carboniferous period to wrest the carbon 

 they required from the oxygen with which it was combined, and 

 eventually to deposit it as the solid material of coal. In our day, 

 the reunion of that carbon with oxygen restores the energy ex- 

 pended in the former process, and thus we are enabled to utilize 

 the power originally derived from the luminous centre of our 

 planetary system. But the agency of the sun in originating coal 

 does not stop at this point. In every period of geological history 

 the waters of the ocean have been lifted by the action of the sun 

 and precipitated in rain upon the'earth. This has given rise to all 

 those sedimentary actions by which mineral substances have been 

 collected at particular localities, and there deposited in a stratified 

 form with a protecting cover to preserve them for future use. 



IS COAL THE MOST ECONOMIC HEAT POWER ? 



The causes which render the application of heat so uneconomic 

 in the steam-engine have been brought to light by the discovery of 

 the dynamical theory of heat ; and it now remains for mechani- 

 cians, guided by the light they have thus received, to devise im- 



