248 THOUGHTS ON THE NATURE AND ORIGIN OF FORCE. 



would seeiii to have almost the germ of a phrenometer,, as if in deflauee 

 of the protestation that " thought cannot be measured." It is but just, 

 however, to admit that this (although in some sense a phrenoscope) is 

 not properly a phreno meter, since the effect determined is really only 

 a resultant of the mental activity, and not its measure. The thermal 

 indication represents (if the expression maj^ be allowed) merely the fric- 

 tion of the mechanism. 



On comparing the modes of derivation offeree in machines (especially 

 in those known as heat-engines) and in animals, we find that the trans- 

 fer is made in substantially the same way. Matter previously raised t(> 

 a chemical state of xwwcr is oxidized, and, in running down by this 

 process of combustion, (whether slow or rapid,) evolves a molecular ac- 

 tivity, which is absorbed and utilized in various ways, according to the 

 exact seat of the transfer. Where deoxidized metals are the source of the 

 power, (as in the galvanic battery.) the process is very similar. In this 

 case, and in mechanisms operated by springs or weights, the potential 

 force is first imparted by human labor. 



The source of power, therefore, in machinery, as in the animal econ- 

 omy', is derived almost entirely from the vegetable kingdom ; in which, 

 matter which has been largely exhausted of its store of force by the en- 

 gine and the animal, and discarded as carbonic acid, water, and other 

 burned products, is raised again by the action of the solar energy to its 

 static plane of chemical potentiality. And it is an interesting and sig- 

 nificant fact that the two great vegetable staples consumed by the dead 

 and by the living mechanisms respectively are identical in composi- 

 tion ; that the cellulose, vv'hich is the principal food of the engine, is chem- 

 ically isomeric with the starch which is the principal fuel of the animal. 

 And the cellulose of the one, equally with the starch of the other, may, 

 as is well known, be converted into sugar. It is hardly necessary to 

 explain in this connection that the mineral coal so largely utilized, is itself 

 but a metamorphosed cellulose ; whose hydrogen and oxygen, (the ele- 

 ments of water,) expelled by geologic heat, have left remaining the car- 

 bon almost in a state of isolated purity. 



IsTor does it detract from the value of this parallelism between the diet 

 of the inorganic and organic worker, that the latter (the animal) has not 

 been so organized as to be capable of availing itself directly of the stored 

 force in woody fiber ; equal though it be to that which it has been 

 adapted to assimilate. 



It is important that we should endeavor to form some conception 

 (however inadequate) of the physical mode of action and of deriva- 

 tion of the various forms of force presented to us. When a bell is struck 

 with a hammer, the metal beneath is carried bj^ the momentum or the 

 vis-viva of the blow, beyond its condition of equilibrum due to the 

 rigidity or molecular adhesion of the material ; and then instantly recoil- 

 ing, thus sets up a vibration counting tens, hundreds, or thousands 

 to the second, according to the inertia, or the mass set in motion ; which 



