Red. 0. Fisher— Contraction of Rocks in Cooling. -09 



now Borry that I said anything about the condition of the moulds ; 

 for tho sontonco might have been just as ■well entirely left out. It 

 was quite immaterial to my argument. 



As Mr. Forbes did not state in liis paper in tho Chemical News 

 that the blocks of slag were devitrified as cast, it was surely 

 pardonable in mo to suppose tho contrary, liaviug been told of the 

 slow process of cooling needful to dovitrify the Kowley rag. And 

 I do not even now feel convinced that a slag cooled thus quickly 

 enters into the normal stony condition of an igneous rock. 



Mr. Forbes does not find fault with the number 0-OGO, as express- 

 ing the final contraction of the Eowley rag. If that number be 

 used in the place of 0-09, which I have employed, the only part of 

 my paper that will be affected by it will be the rough estimate of the 

 height of mountain chains, caused by a contraction supposed equal to 

 the latter number. These will have to be lowered, in the ratio of 0-64 

 to 1, or nearly in that of two to three ; and thus the results will be 

 made to accord with nature better. But I must repeat the caution, 

 that no attempt is made here to arrive at a definite result, because 

 we have no right to assume that an upper shell of the earth, 

 of the thickness I have supposed, has contracted to the same amount 

 as the Eowley rag did, in passing from a fused to a devitrified 

 state. Its contraction may have been less or it may have been 

 greater. Yet I think we may assume that it has been of the same 

 order of magnitude, which is all that I intend to assert. All that 

 my general argument requires is the admission that heated rocks 

 contract on cooling. It is not afi'ected by the question whether the 

 earth be noio solid, or fluid, or semifluid, internally. If it be fluid, 

 that condition will more easily explain volcanic action, though it 

 seems possible the solid condition (to which I incline) may be com- 

 patible with my speculation as to its cause. 



The somewhat lengthy investigation as to the condition of pressure 

 in the interior, on the supposition that the earth is solid, is intended 

 not to leave that case unprovided for. 



Finally, a word for the mathematicians, of whom I make no pre- 

 tension to be one. So long as certain questions cannot be touched 

 without their aid, their vocation will be a needful and an honour- 

 able one. The present feud seems a re-enactment of the fable of the 

 belly and the members. Mathematics has been likened to a mill. 

 I will extend the simile, and call the mathematician, not the miller, 

 but the millwright. The experimentalist is the grower of the corn. 

 If the com is good so will be the flour. But though bad com be 

 once put in, and bad flour come out, the mill is as good as ever ; and 

 so, if a false numerical result be introduced into a problem, the mere 

 substitution of a correct one will bring a correct result. Few men 

 can be accomplished on all sides, and the shortcomings of the 

 mathematician, as an experimentalist, will best be met by kindly 

 suggestions from his more accomplished fellow workers in other 

 portions of the vast fields of science. 



