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haps find the solution of the difficulty in reconciling the results 

 of the calculation of the rate of secular cooling with the results 

 deduced from the denudation or deposition of strata in the 

 following consideration. If there have been a gradual and con- 

 tinual dissipation of energy, there will on the whole have been 

 a gradual decrease in the violence or rapidity of all physical 

 changes. When the gunpowder in a gun is just lighted, the 

 energy applied in a small mass produces rapid and violent 

 changes ; as the ball rushes through the air it gradually loses 

 speed ; when it strikes rapid changes again occur, but not so 

 rapid as at starting. Part of the energy is slowly being diffused 

 through the air ; part is being slowly conducted as heat from 

 the interior to the exterior of the gun, only a residue shatters 

 the rampart, and that residue, soon changing into heat, is finally 

 diffused at a gradually decreasing rate into surrounding matter. 

 Follow any self-contained change, and a similar gradual diminu- 

 tion on the whole will be observed. There are periods of greater 

 and less activity, but the activity on the whole diminishes. 

 Even so must it have been, and so will it be, with our earth. 

 Extremes tend to diminish ; high places become lower, low 

 places higher, by denudation. Conduction is continually en- 

 deavouring to reduce extremes of heat and cold ; as the sun's 

 heat diminishes, so will the violence of storms ; as inequalities 

 of surface diminish, so will the variations of climate. As the 

 external crust consolidates, so will the effect of internal fire 

 diminish. As internal stores of fuel are consumed, or other 

 stores of chemical energy used up, the convulsions or gradual 

 changes they can produce must diminish ; on every side, and 

 from whatever cause changes are due, we see the tendency to 

 their gradual diminution of intensity or rapidity. To say that 

 things must or can always have gone on at the present rate is a 

 sheer absurdity, exactly equivalent to saying that a boiler fire 

 once lighted will keep a steam engine going for ever at a 

 constant rate. To say that changes which have occurred, or will 

 occur, since creation, have been due to the same causes as those 

 now in action ; and further, that such causes have not varied in 

 intensity according to any other laws than those which now 

 prevail, is, we believe, a correct scientific statement ; but then 

 we contend that those causes must and do hourly diminish in 



