HEAT. 67 



about in an immeasurably long time by the mutual inter- 

 actions of physical forces, the which, by eliminating impedi- 

 ments, have produced a machinery more perfect than the 

 rapid performances of art. Even with inorganic forces the 

 perfection of natural action and natural selection is wonderful. 

 The following instance may help to explain my meaning : 

 In some of the fissures of the limestone rocks to the west of 

 Oystermouth, near Swansea, may be seen frills formed by 

 bleached oyster shells, which in course of ages have been 

 washed by the tide into them. So perfect is the filling up of 

 these fissures that hardly a crevice is left between the shells, 

 and so close the fitting that great force is required to remove 

 a single shell. A frill of many yards' length is thus formed 

 which it would much puzzle a human artificer to imitate. 



A speculation has been thrown out by Sir W. Thomson, 

 that, as a certain amount of heat results from mechanical 

 action, chemical action, &c., and these other forces resolve 

 themselves into heat, as this heat is radiated into space, there 

 must be a gradual diminution of temperature for the earth, 

 by which expenditure, however slow, being continuous, it 

 would ultimately be cooled to a degree incompatible with the 

 existence of animal and vegetable life in short, that the 

 earth and the planets of our system are parting with more 

 heat than they receive, and are therefore progressively cool- 

 ing. Geological researches seemed at first to support this 

 view, as they showed that the climate of many portions of 

 the terrestrial surface was at remote periods hotter than at 

 the present time: the animals whose fossilised remains are 

 found in ancient strata have their organism adapted to what 

 we should now term a hot climate.* Mr. Balfour Stewart 

 sums up the views of Thomson as follows : ' We are led to 

 look at a beginning in which the particles of matter were in a 

 diffuse chaotic state, but endowed with the power of gravita- 

 tion, and we are led to look to an end in which the whole 

 universe will be one equally heated inert mass, and from 

 which everything like life or motion or beauty will have 

 utterly gone away.' I have some difficulty in seeing how, on 



* ^ee, however, Mr. Croll's views, post. 

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