NATURE AS DRAMA AND ENGINERY. 501 



a stone wall or a wooden door becomes as permeable as plate 

 glass to sunshine. All this lias long been suspected by the phys- 

 icists Avho, among equally significant facts, have noticed that an 

 explosive is set off less by the violence of its detonator than by 

 the sympathy of rhythm between the two. Dr. Lothar Meyer, in 

 his Modern Theories of Chemistry, discusses the ingenious theo- 

 ries which on kinetic principles explain many of the chief quali- 

 ties of matter color, refrangibility, volatility, fusibility, and 

 ability to yield heat in combustion. He regards this field as that 

 which bears most promise for the chemical investigator, and fol- 

 lows Berthollet in maintaining that chemistry is but a branch of 

 the larger science of mechanics. In corroboration of this view a 

 thousand facts might be cited a typical piece of evidence is that 

 adduced by Mr. Witt, who finds that the stability of the azo-ben- 

 zene dyes turns upon the nicety with which their acid and basic 

 functions balance each other. 



In leaving the field of molar for that of molecular mechanics, 

 it has been already noted that friction need no longer be reck- 

 oned with ; consequences equally important result from the fact 

 that now masses of extreme minuteness are in play. Sir William 

 Thomson (Nature, vol. i. p. 551) has estimated the diameter of 

 molecules as at most Teoirio otttf of an inch in diameter ; cubical 

 molecules of this size containable in a cubic inch of space would 

 have a total surface of one square mile and one seventh, which 

 implies that in molecular mechanics superficial forces must count 

 for vastly more than in molar mechanics. Another result follows 

 from molecular minuteness of dimensions an enormously in- 

 creased capacity for motion. The smaller a wheel the more 

 swiftly can it be rotated without being parted by centrifugal 

 force, and therefore the more motion can it contain. With a 

 molecule probably, with an atom certainly, centrifugal force has 

 no separating power. How great the momentum of specific molec- 

 ular motions will appear in computing that duo to temperature, 

 in the case of a pound of unfrozen water at the zero of the centi- 

 grade scale. According to the determinations of Lord Rayleigh, 

 a pound of water, in falling through one degree of temperature, 

 liberates heat equal to that generated were the mass to fall from 

 a height of fourteen hundred and two feet to the surface of the 

 earth. Therefore, in first becoming ice, and then falling in tem- 

 perature through two hundred and seventy-three degrees, it parts 

 with an amount of energy equal to lifting the jjound of water 

 some fifty-seven and one third miles from the surface of the earth, 

 leaving out of view, for simplicity's sake, the diminution in the 

 attraction of the earth as the mass is lifted. Prof. Dewar, in his 

 recent remarkable experiments at a temperature of 200 below 

 zero, has found reason to believe that at absolute zero the electri- 



