86 SCIENCE IN THE LAST HALF CENTURY. 



compared, thougb it professes a similar object, is unfortunately per- 

 meated by a thorougbly unscientific spirit, and its author liad no ade- 

 quate acquaintance with the physical sciences even of his own time. 



The doctrine of evolution, so far as the present physical cosmos is 

 concerned, postulates the fixity of the rules of operation of the causes' 

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

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

 energy, the orderly evolution of physical nature out of one substratum 

 and one energy implies that the rules of action of that energy should 

 be fixed and definite. In the past history of the universe back to that 

 point, there can be no room for chance or disorder. But it is possible 

 to raise the question whether this universe of simplest matter and defi- 

 nitely operating energy, which forms our hypothetical starting i)oint, 

 may not itself be a product of evolution from a universe of such jnatter, 

 in which the manifestations of energy were not definite, — in which, for 

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

 others, or for the same units at one time and not at another, — and which 

 would therefore be a real epicurean chance-world? 



For myself, I must confess that 1 find the air of this region of specu- 

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

 in '' ignoramus et iguorabimus." 



OTHER SCIENTIFIC ACHIEVEMENTS. 



The execution of my further task, the indication of the most im- 

 portant achievements in the several branches of pliysical science during 

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

 choice; and by the difficulty which every one, but a specialist in each 

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

 coveries which strike the imagination by their novelty, or by their 

 ])ractical influence, and those unobtrusive but pregnant observations 

 and experiments in which the germs of the great things of the future 

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

 chronicle of the events which I have to notice. 



In pliysics and chemistry, the old boundaries of which sciences are 

 rapidly becoming effaced, one can hardly go wrong in ascribing a pri- 

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

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

 ])ressure and of heat on the other. Almost all, even the most refrac- 

 tory, solids have been vaporized by the intense heat of the electric arc; 

 and the most refractory gases have been forced to assume the liquid, 

 and even the solid, forms bythe combination of high i)ressure with 

 intense cold. It has further been shown that there is no discontinuity 

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



