ON THE CONSERVATION OF FORCE. 299 



motive powers formerly known is that it is not restricted to a 

 particular place. The store of coal and the small quantity of 

 water which are the sources of its power can be brought every- 

 where, and steam-engines can even be made movable, as is the 

 case with steam-ships and locomotives. By means of these 

 machines we can develop motive power to almost an indefinite 

 extent at any place on the earth's surface, in deep mines and 

 even on the middle of the ocean ; while water and wind mills 

 are bound to special parts of the surface of the land. The loco- 

 motive transports travellers and goods over the land in numbers 

 and with a speed which must have seemed an incredible fable to 

 our forefathers, who looked upon the mail-coach with its six 

 passengers in the inside, and its ten miles an hour, as an enor- 

 mous progress. Steam-engines traverse the ocean independently 

 of the direction of the wind, and, successfully resisting storms 

 which would drive sailing-vessels far away, reach their goal at 

 the appointed time. The advantages which the concourse of 

 numerous and variously skilled workmen in all branches offers 

 in large towns where wind and water power are wanting, can 

 be utilised, for steam-engines find place everywhere, and supply 

 the necessary crude force; thus the more intelligent human 

 force may be spared for better purposes ; and, indeed, wherever 

 the nature of the ground or the neighbourhood of suitable lines 

 of communication present a favourable opportunity for the 

 development of industry, the motive power is also present in the 

 form of steam-engines. 



We see, then, that heat can produce mechanical power; but 

 in the cases which we have discussed we have seen that the 

 quantity of force which can be produced by a given measure of 

 a physical process is always accurately defined, and that the 

 further capacity for work of the natural forces is either 

 diminished or exhausted by the work which has been performed. 

 How is it now with Heat in this respect? 



This question was of decisive importance in the endeavour 

 to extend the law of the Conservation of Force to all natural 

 processes. In the answer lay the chief difference between the 

 older and newer views in these respects. Hence it is that many 



