Source of Motions upon the Earth. 303 



influences, when they are predominant in power, lead matter away 

 from a certain point. The mechanical and the chemical forces of 

 terrestrial matter, when their turn of supremacy comes, bring it back 

 to that point again ; and all the motions we have considered, take 

 place between these two extremes, and by virtue of this antagonism 

 and alternate action of the two classes of force. 



We have, in this manner, a vast number of " circles of eternal 

 motion" produced, which, weaving and interweaving among them- 

 selves, connect and maintain each other, and give rise to the present 

 order of things. Here we may attempt to point out the individual 

 operation, and the limits of the forces derived from external nature, 

 and of the vital forces respectively. The motions which we termed 

 physical, or those which are independent of life, as the tides, winds, 

 evaporation, running water, and the like, are all of them derived 

 from the forces of matter external to the earth, so that their measure- 

 ment would give the amount of that lunar, solar, and, perhaps, stel- 

 lar force so applied. The motions of organised matter, again, come 

 from a compound source, partly from external nature, and chiefly 

 from the sun, and partly from vital force. It is unknown what the 

 exact operation of each of these is, but it seems not impi-obable, that, 

 in the case of plants at least, the solar forces act chiefly by destroy- 

 ing or neutralising chemical affinity, and by rendering the molecules 

 of matter more mobile ; and that the operation of the vital force con- 

 sists in completing the decomposition of the inorganic matter, the 

 affinities of which have been weakened by light, in arranging the 

 molecules of that matter in organic combinations, and in preserving 

 them from the attacks of the chemical forces, after they are so ar- 

 ranged.* What the action of the sun is upon animal beings, apart 

 from its heat, and how far these are directly dependent upon it, is 

 very uncertain. But the action of the sun, and their dependence 

 upon it, does not seem to be so great as it is in the case of plants, 

 and it would seem that the vital forces are those upon which their 

 existence chiefly depends. It has, therefore, been attempted to be 

 shewn, that all the motions we have mentioned are the result of 

 vital forces, and of the forces of extei'nal nature. It is true that the 

 physical and the chemical forces, inherent in terrestial matter, do 

 play a part in the production of motion, but it is only a secondary 

 one. They resemble the weights of a clock, which, by descending, 

 produce a number of motions ; but the force which these weights 

 exert, is communicated, or put into them as it were, by the hand 

 which rolled them up, and the motions which they' produce are the 



* See a learned and able paper, by Dr Alison of the University of Edinburgh, 

 on Vital Affinity, in Transactions of the Royal Society of Edinburgh, vol. xvi., 

 and reprinted in this Journal, Nos. Ixxxi. and Ixxxii. 



