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Show 156 ACTIO~ OF HEAT. as they are in their intensity, and majestic in th~r effects, may have room and scope enough form - ing great mountains. . It is true that considerable portiOns of matter are thrown up at a few points by volcanoes on the. land; but still it is doubtful whether any one mountam has ever added permanently to its height ~y that mean~. The present Vesuvius is to observa~wn a volcamc pile, but it is surrounded by th~ remam.s of a former and loftiermountain, the summit of which has f~llen in after the former volcano has excavated th~ mterior. We know, too, that when the connexwn of volcanoes with the sea i~ cut off, the volcanoes become still and cool by slow degrees. Thus we can seei as the power of h~at has reapy no material limit, how it can work, .m successive exhaustions and renovations, the cont~nents and the oceans, just as i~ revolving. seaso~s It rene~s the plants and the. a~1I~als, and JUSt as m t~e reci~roc<:J actions of contammg vesselH and c~ntamed :flmds, Jt repairs the waste of plant~ and amtnals . by successive assimilations of nounshment. This heat, ~e have already seen, is~ eyen in the strength of .I~s working, not a thing that would measure one hau s breadth by the scale, or cause the thousandth part of the smallest grain to mount up on the balance ; but still it can lay upon the whole glo~e, a~d al! the material works of the Creator, the gnpe ot a gi~nt, which nothing can resist,-that.before It the ancient mountains are liO'htcr than thistle-down, and the fathomless strata ~f the earth itself are weaker than cobwebs. What then shall we think of Him who could with one word, or even without. word or wish, create this mighty energy, and send It dow~ to us in a garment as lovely as a s~mbeam, and ~s gayly tinted as a rainbow, and make It our b.est frtend ~nd ()Ur most obedient servant,-and, savmg where Immortal spirit is concerned, make it throughout all aature life itself! MOTION. 157 SECTION VII. Observation of Air and Water. As we can know and contemplate the powers with which nature works only through the medium of those substances in which they arc manifested, a considerable portion of that which would, perhaps, with mor~ propriety, come in under this or some of the succeeding parts of the book, has been already anticipated, and what remains to be said may, in some instances, have the appearance of repetition. But that is unavoidable; for if we are to view nature as it exists -living nature, we nwst view it in its connexion. There is no dissecting till after death; and then the very finest anatomy that can be practised gives us only disjointed members. But the observer wi shes to know nature in its activity and life; and, 1herefore, there is no possibility of noticing any one thing usefully to him without a glance at collateral things. In the case of the great agencies of gravitation and cohesion, and light and heat, and motion and resistance, that is especially necessary, inasmuch as, apart from the subject in which their effects are displayed, we have not the slightest conception or means of knowing any one of these. There is no weight, unless there is something that is heavy, and has other properties besides weight; there can be no cohesion, unless there is matter to cohere; light never appears but ~vhen it illuminates something; we know nothing of heat, unless there is something that is warmed by resistance to it; and we can know that there is motion, not merely when something moves, but when there is some other thing 0 |