CONTINUITY. 201 



This may bear on certain recent speculations on the dissi- 

 pation of force by heat radiation. 



Here also we have as to force-absorption, an analogous 

 result to that of the formation of coal from carbonic acid and 

 water ; and though this is a mere illustration, and cannot be 

 expected to become economical on a large scale, still it and 

 similar examples may calm apprehension as to future means 

 of supplying heat, should our present fuel become exhausted. 

 As the sun's force, spent in times long past, is now returned to 

 us from the coal which was formed by its light and heat, so 

 the sun's rays, which are daily wasted, as far as we are 

 concerned, on the sandy deserts of Africa, may hereafter by 

 chemical or mechanical means, be made to light and warm 

 the habitations of the denizens of colder regions. The tidal 

 wave is, again, a large reservoir of force hitherto almost 

 unused. . 



The valuable researches of Professor Tyndall on radiant 

 heat afford many instances of the power of localising, if 

 the term be permitted, heat which would otherwise be 

 dissipated. 



The discoveries of Graham, by which atmospheric air, 

 drawn through films of caoutchouc, leaves behind half its 

 nitrogen, or, in other words, becomes richer by half in oxygen, 

 and hence has a much increased potential energy, not only 

 show a most remarkable instance of physical molecular action 

 merging into chemical, but afford us indications of means of 

 storing up force, much of the force used in working the aspi- 

 rator being capable at any period, however remote, of being 

 evolved by burning the oxygen with a combustible. 



What changes may take place in our modes of applying 

 force before the coal-fields are exhausted it is impossible to 

 predict. Even guesses at the probable period of their exhaus- 

 tion are uncertain. There is a tendency to substitute for 

 smelting in metallurgic processes, liquid chemical action, which 

 of course has the effect of saving fuel ; and the waste of fuel 

 in ordinary operations is enormous, and can be much econo- 

 mised by already known processes. It is true that we are, at 

 present, far from seeing a practical mode of replacing that 

 granary of force, the coal-fields ; but we may with confidence 



