32 THE POPULAR SCIENCE MONTHLY. 



Every one of these is within the jurisdiction of the laws of mechanics, 

 even when the motions are so exalted in degree and dignity as to seem 

 of other stock than their real parents. Or, to change the metaphor, 

 the tortuous labyrinth of the whole series diverges by clear and con- 

 tinuous avenues from one simple highway, where the elementary laws 

 of motion are visibly obeyed. 



The consistences of matter, as well as its properties, illustrate in a 

 remarkable manner the principle of continuity. Sir William Herschel 

 long ago ventured on general grounds to predict that the solid, liquid, 

 and gaseous states of matter would be found to shade off impercepti- 

 bly into each other. Twenty years afterward, the labors of Prof. An- 

 drews, of Belfast, proved the great astronomer right. By the most 

 ingenious appliances, he detained for convenient inspection processes 

 of transition from gas to liquid, which, in their ordinary progress, co- 

 alesce so abruptly as to seem instantaneous. In some familiar cases 

 we can perceive changes of the same kind going on; as, for example, 

 in the melting of wax we can follow the alteration from brittle hard- 

 ness to plasticity, and thence to viscosity and liquefaction. From 

 facts such as these, here very briefly indicated, has arisen the convic- 

 tion that all matter can assume any of the three consistences. Fara- 

 day liquefied, by cold and great pressure, several of what had been 

 called permanent gases, and improvements in the means of producing 

 pressure and cold will doubtless enable us in the future to liquefy the 

 remainder. Although the greatest heat we can bring to bear on car- 

 bon does not fuse it, still the tendency of our knowledge is to induce 

 us to believe that coal in burning for a brief instant, too short for ob- 

 servation, exists in the liquid state. A second of time is divisible into 

 millionths quite as perfectly as a geological cycle. 



The thread of continuity has, in a variety of cases, been established 

 in the laboratory. No two physical facts would seem to stand more 

 decidedly apart than chemical union and mechanical admixture, yet 

 we find them inextricably joined when we add sulphuric acid and 

 water together. In all possible percentages do these liquids chemi- 

 cally combine, and this at variance with the generally-obeyed law of 

 definite proportions. The same departure from the usual rule also 

 obtains among other complex unions, and corroborates what first 

 principles affirm namely, that chemical forces are but intense and 

 involved mechanical ones. 



In the progress of science there has been much speculation as to 

 the method by which light, electricity, and gravitation, are propa- 

 gated through space. It is the old question again, " Can matter act 

 where it is not?" Newton found the idea inconceivable, and ima- 

 gined an ether as the vehicle of motions between the suns and planets 

 of the universe. This position has been criticised by Mill, who says 

 that inconceivableness is no test of truth, and who asserts, with a lack 

 of his usual caution, that scarcely any living thinker of eminence now 



