624 ^^^ POPULAR SCIENCE MONTHLY. 



about it. But, not wishing to leave anything uninvestigated, he goes 

 round to the other side of the wall. There he finds that one end of the 

 shaft comes througli it, and is in mechanical connection with either a 

 steam-engine or a water-wheel ; and, by watching what occurs when 

 its motion is checked and renewed, he sees that the engineer shuts 

 off, or turns on, either the steam generated in the boiler of the steam- 

 engine, or the descending water whose motion drives the wheel. 



I shall not weary the patience of such readers as may have followed 

 me 'thus far, by tracing out in like detail the further steps of the in- 

 quiry, but shall land them in the final conclusion now accepted by 

 every man of science — that the power exerted in both these cases is 

 drawn from solar radiation : the fall of the water which gives motion 

 to the water-wheel being merely the return of that which has been 

 pumped up as vapor by the sun's heat ; while the combustion of coal 

 from which steam-power is derived reproduces, as active force, or 

 " energy," the sunshine that exerted itself during the Carboniferous 

 period in dissociating carbonic acid and water into the hydrocarbons 

 of coal and the oxygen of the atmosphere, whose recombination gives 

 forth heat and light. And, if we look still further back for the source 

 of the sun's radiant energy, we should find it, perhaps, in the progres- 

 sive consolidation of the primeval " fire-mist " — nebular matter. 



But whence nebular matter ? And whence the force which draws 

 its particles together, and which manifests itself as light and heat 

 during their consolidation ? Here we come to a wall, to the other side 

 of which we seem at present to have no access. 



But is there no other side ? Does not the whole course of the pre- 

 ceding inquiry show the unsatisfaction (if I may revive an obsolete 

 word) of resting in any inherent " potency " of matter as the ultima 

 ratio of the existing cosmos ? If we think the man foolish who sup- 

 poses the main shaft of a cotton-mill to turn of itself merely because 

 he sees it apparently end in a wall which conceals from him the source 

 of its motive power, are we not really chargeable with the like folly 

 if we attribute self-motion to the ultimate molecules of matter, merely 

 because the power that moves them is hid from our sight ? The mere 

 physicist may see no possible way further. But there is a philosophy 

 which has fully as true and as broad a basis in man's psychical expe- 

 rience as can be claimed for the fabric of physical science ; and, in the 

 admirable words of the great master I have already quoted (Sir John 

 Herschel, in his " Familiar Lectures on Scientific Subjects," p. 460), 

 I shall sum up an argument which this paper is intended rather to illus- 

 trate and enforce by an appeal to the familiar facts of consciousness 

 than to present in strict logical form : 



In tlie mental sense of effort, clear to the apprehension of every one who 

 has ever performed a voluntary act, which is present at the instant when the 

 determination to do a thing is carried out into the act of doing it, we have a 

 consciousness of immediate and personal causation which can not be disputed 



