86 SCIENCE IN THE LAST HALF CENTURY. 



compared, tbongli it professes a similar object, is nnfortiiiiately per- 

 meated by a thorougbly unscientific spirit, and its antlior bad no ade- 

 quate acqnaintiince witb tbe pbysical sciences even of bis own time. 



The doctrine of evolution, so far as tbe present pbysical cosmos is 

 concerned, postulates tbe fixity of tbe rules of operation of tbe causes 

 of motion in tbe material universe. If all kinds of matter are modifica- 

 tions of one kind, and if all modes of motion are derived from tbe same 

 energy, tbe orderly evolution of pbysical nature out of one substratum 

 and one energy implies tbat tbe rules of action of tbat energy sbould 

 be fixed and definite. In tbe i)ast bistorj^ of tbe universe back to tbat 

 l^oiut, tbere can be no room for cbauce or disorder. Bnt it is possible 

 to raise tbe question wbetber tbis universe of simplest matter and defi- 

 nitely operating energy, wbich forms our bypotbetical starting point, 

 may not itself be a product of evolution froju a universe of sucb matter, 

 in wbicb tbe manifestations of energy were not definite, — in wbicb, for 

 example, our laws of motion beld good for some units and not for 

 others, or for tbe same units at one time and not at another, — and wbic;b 

 would tberefore be a real epicurean cbance-world? 



For myself, I must confess tbat I find tbe air of tbis region of specu- 

 lation too rarefied for my constitution, and I am disposed to take refuge 

 in "ignoramus et ignorabimus." 



OTHEJl SCIENTIFIC ACHIEVEMENTS. 



The execution of my furtber task, tbe iudication of tbe most im- 

 portant achievements in tbe several braucbes of physical science during 

 tbe last fifty years, is embarrassed by tbe abundance of tbe objects of 

 choice ; and by tbe difficulty wbicb every one, but a specialist in eacb 

 department, must find in drawing a due distinction between tbe dis- 

 coveries wbicb strike tbe imagination by tbeir novelty, or by their 

 l)ractical influence, and those unobtrusive but pregnant observations 

 and experiments in wbicb tbe germs of tbe great tbings of the future 

 really lie. Moreover, my limits restrict me to -little more than a bare 

 chronicle of the events wbicb I have to notice. 



In physics and cbemistry, the old boundaries of wbicb sciences are 

 ra})idly becoming effaced, one can hardly go wrong in ascribing a pri- 

 mary value to tbe investigations into the relation between tbe solid, 

 liquid, and gaseous states of matter on tbe one hand, and degrees of 

 ])ressure and of beat on tbe other. Almost all, even tbe most i^efrac- 

 tory, solids have been vaporized by tbe intense beat of tbe electric arc; 

 and tbe most refractory gases bave been forced to assume tbe liquid, 

 and even the solid, forms by the combination of bigb pressure witb 

 intense cold. It bas further been shown that tbere is no discontinuity 

 between these states — that a gas passes into the liquid state tlirougb a 

 condition which is neither one nor the other, and that a liquid body 

 becomes solid, or a solid liquid, by the intermediation of a condition in 

 which it is neither truly solid nor truly liquid. 



