MAN AS THE INTERPRETER OF NATURE. 6 97 



employed in popular phraseology ; often (as Mr. Mill has shown) to 

 designate the occurrence that immediately preceded the effect as 

 when it is said that the spark which falls into a harrel of gunpowder 

 is the cause of its explosion, or that the slipping of a man's foot off the 

 rung of a ladder is the cause of his fall. But even a very slightly- 

 trained intelligence can distinguish the power which acts in each case 

 from the conditions under which it acts. The force which produces 

 the explosion is locked up, as it were, in the powder ; and ignition 

 merely liberates it by bringing about new chemical combinations. 

 The fall of the man from the ladder is due to the gravity which was 

 equally pulling him down while he rested on it ; and the loss of sup- 

 port, either by the slipping of his foot or by the breaking of the rung, 

 is merely that change in the material conditions which gives the power 

 a new action. 



Many of you have doubtless viewed with admiring interest that 

 truly wonderful work of human design, the Walter printing-machine. 

 You first examine it at rest ; presently comes a man who simply pulls 

 a handle toward him, and the whole inert mechanism becomes instinct 

 with life the blank paper, continuously rolling off the cylinder at one 

 end, being delivered at the other, without any intermediate human 

 agency, as large sheets of print, at the rate of 15,000 in an hour. Now, 

 what is the cause of this most marvellous effect ? Surely it lies essen- 

 tially in the power or force which the pulling of the handle brings to 

 bear on the machine from some extraneous source of power, which we 

 in this instance know to be a steam-engine on the other side of the 

 wall. This force it is, which, distributed through the various parts of 

 the mechanism, really performs the action of which each is the instru- 

 ment ; they only supply the vehicle for its transmission and applica- 

 tion. The man comes again, pushes the handle in the opposite direc- 

 tion, detaches the machine from the steam-engine, and the whole comes 

 to a stand; and so it remains, like an inanimate corpse, until recalled 

 to activity by the renewal of its moving power. 



But, say the reasoners who deny that force is any thing else than 

 a fiction of the imagination, the revolving shaft of the steam-engine is 

 " matter in motion ; " and, when the connection is established between 

 that shaft and the one that drives the machine, the motion is com- 

 municated from the former to the latter, and thence distributed to the 

 several parts of the mechanism. This account of the operation is just 

 what an observer might give who had looked on with entire ignorance 

 of every thing but what his eyes could see ; the moment he puts his 

 hand upon any part of the machinery and tries to stop its motion, he 

 takes as direct cognizance, through his sense of the effort required to 

 resist it, of the force which produces that motion as he does through 

 his eye of the motion itself. 



Now, since it is universally admitted that our notion of the ex- 

 ternal world would be not only incomplete, but erroneous, if our visual 



