380 FALLACIES. 



previous motion ; the impulse or impact of some other 

 body. It was very long before the scientific world 

 could prevail upon itself to admit attraction and repul- 

 sion (i.e. spontaneous tendencies of particles to approach 

 or recede from one another) as ultimate laws, no more 

 requiring to be accounted for than impulse itself, if 

 indeed the latter were not, in truth, resolvable into 

 the former. From this same source arose the innu- 

 merable hypotheses to explain those classes of motions 

 which appeared more mysterious than others because 

 there was no obvious mode of attributing them to 

 impulse, as for example the voluntary motions of the 

 human body. Such were the interminable systems of 

 vibrations propagated along the nerves, or animal spirits 

 rushing up and down between the muscles and the 

 brain: which, if the facts could have been proved, 

 would no doubt have been an important addition to 

 our knowledge of physiological laws; but the mere 

 invention, or arbitrary supposition of them, could not 

 unless by the strongest delusion be supposed to render 

 the phenomena of animal life more comprehensible, 

 or less mysterious. Nothing, however, seemed satis- 

 factory, but to make out that motion was caused by 

 motion; by something like itself. If it was not one 

 kind of motion it must be another. In like manner 

 it was supposed that the physical qualities of objects 

 must arise from some similar quality, or perhaps only 

 some quality bearing the same name, in the particles 

 or atoms of which the objects were composed; that a 

 sharp taste, for example, must arise from sharp 

 particles. And reversing the inference, the effects 

 produced by a phenomenon must, it was supposed, 

 resemble in their physical attributes the phenomenon 

 itself. The influences of the planets were supposed 

 to be analogous to their visible peculiarities: Mars, 



