250 THOUGHTS ON THE NATURE AND ORIGIN OF FORCE. 



ships are as feathers,) and all their weariug actiou upou coast aud river 

 shores, are due partly to the siiu's attractiou, but in a much larger 

 degree to that of the moon, an outlying portion of the ea^rth's former 

 equator.* 



Xot pausing to notice the various theories — more or less plausible — of 

 chemical or of aqueous agency in earthquake waves and in volcanic 

 ejections, we may, for the present purj)ose, regard these occasional out- 

 breaks as the readjustments and vents of wide-spread pressure, from 

 insensible settlings by the shrinkage of the earth's crust, resulting from 

 the extremely slow cooling of the interior mass: the hardened' envel- 

 ope of stone or rock, a poorly conducting material, acting as a blanket 

 which almost arrests the escape of the internal heat. And this heat, 

 again, may be regarded but as a feeble residuum of that cosmical ac- 

 tivity still notable in the suu aud other stars. 



Finding thus from observation that the sun is the great source of 

 energy — static and kinetic — in almost all terrestrial phenomena, from the 

 meteorological to the geographical, from the geological to the biological, 

 we can only conclude that in the expenditure aud conversion of molecu- 

 lar movements, derived from the sun's rays, must be sought the motive 

 power of all this infinitely varied phantasmagoria. Thus, especially in 

 the great store of organic force existing in the vegetable world, we 

 must suppose that these subtle actinic vibrations, several times finer 

 and higher even than those recognized as heat, have such relation to 

 the molecular masses and inertia as by "forced" vibrations to overcome 

 the powerful attraction of chemical affinities, and fairly to shake the 

 particles into isolation, at the same time that other motions, photic and 

 thermal, are expended in occluding in the plant structure the carbon 

 thus deoxidized and divorced. 



Tracing back these potent quiverings through the ninety-one and a 

 half millions of miles of ethereal highway, along whose inconceivable 



* Mayer, iu his rcuiarkaljle Dijnamik clcs Himmels, discussing the retarding effect of 

 the tidal Avavc on the eartli's rotation by reason of friction, calculates that this is suf- 

 ficient to have lengthened the day, within the last two thousand five hundred years, 

 by one-sixteenth of a second. On the other hand, since the globe must have cooled 

 somewhat vithin this xjcriod, (estimated at one-fourteenth of a degree Centigrade, or 

 about one-eighth of a degree Fahrenheit, for the whole mass,) this would involve a con- 

 traction of the earth's radius (or a dei^ressiou of its surface) amounting to about fourteen 

 feet nine inches. Such a diminution of the equatorial leverage of rotation necessarily 

 implies an acceleration of the motion, or a shortening of the day, very nearly equal to 

 the opposite tendency, and counterbalancing it. " When our earth was in its youth its 

 velocity of rotation must have increased to a very sensible degree, on account of the 

 rapid cooling of its very hot mass. This accelerating cause gradually diminished, and 

 as the retarding jiressure of the tidal wave remains nearly constant, the latter must 

 finally prei^ouderate, and the velocity of rotation, therefore, continually decrease." 

 (i. E. D. FkU. Mag., 1863, Vol. XXV, pp. 409 aud 4-27.) During the historical period, 

 accordingly, it ajipears that the length of the day has reached its minimum, and has 

 been sensibly constant or uniform, the rotation having greatly increased in the distant 

 past, as it must as greatly decrease iu the distant future. 



