990 Dynamic Theory. 



mode of motion, we have no reason to doubt. We know that motion 

 can no more be lost or cease to be, than that gold can be annihilated. 

 It may be locked up temporarily, as potential energy, but it can never 

 become anything else than energy, either on a strain or in motion. It is 

 transferred from one body to another, each body in turn moving accord- 

 ing to its peculiar constitution, and ceasing to move only when its mo- 

 tion is communicated to another. In this way we are able to trace the 

 vibratory motion of the ether to the eye, where it ceases in that form, 

 and is succeeded by a molecular vibration, called a nerve current, which 

 passes to a cell in the sensorium, and is succeeded there by the motion 

 called green, or blue, or whatever it happens to be. 



Again, the lecturer observes : ' 'The sense organ, the nerve, and the 

 sensorium taken together constitute the sensiferous apparatus. They 

 make up the thickness of the wall between the mind, as represented by 

 the sensation, 'muskiness, ' and the object as represented by the particle 

 of musk in contact with the olfactory epithelium," in other words, be- 

 tween the sensation and the object from which it was reflected. Then 

 he goes on : "It will be observed that the sensiferous wall and the ex- 

 ternal world are of the same nature ; whatever it is that constitutes 

 them both is expressible in terms of matter and motion. Whatever 

 changes take place in the sensiferous apparatus are continuous with and 

 similar to those which take place in the external world. But with the 

 sensorium matter and motion come to an end, while phenomena of an- 

 other order, or immaterial states of consciousness, make their appearance. 

 How is the relation between the material and immaterial phenomena to 

 be conceived? " Three hypotheses have been proposed. 



11 The first is that an immaterial substance of mind exists ; and that 

 it is affected by the mode of motion of the sensorium, in such a way as 

 to give rise to the sensation. The second is that the sensation is a di- 

 rect effect of the mode of motion of the sensorium, brought about with- 

 out the intervention of any substance of mind. The third is that the 

 sensation is neither directly, or indirectly, an effect of the mode of mo- 

 tion of the sensorium, but that it has an independent cause. Properly 

 speaking, therefore, it is not an effect of the motion of the sensorium, 

 but a concomitant of it." 



The lecturer holds that neither of these can be proved, but prefers 

 the second one as the simplest. Yet he says the third cannot be refuted, 

 and of the first he observes, ' ' An immaterial substance is perfectly 

 conceivable. In fact it is obvious that if we possessed no sensations, 

 but those of smell, and hearing, we should be unable to conceive a ma- 

 terial substance. We might have a conception of time, but could have 

 none of extension, or of resistance, or of motion, and without the three 

 latter conceptions, no idea of matter could be formed. Our whole knowl- 



