MIND AND ENERGY 363 



sufficiently powerful microscope, I should be able to perceive the 

 whole chain, and, within narrow limits, to think of it in terms of 

 causation. Even now my perceptive powers are such that they 

 supply me with materials which enable me to imagine it. But no 

 microscope, however powerful, could enable me to perceive how 

 the molecular movements in the brain result in mind. Even if I 

 could see the movements of the molecules of another man's brain, 

 even if I learned that certain movements in certain regions of his 

 brain always coincided with certain of his feelings and thoughts, I 

 should yet be unable to perceive the link between the two trains 

 of happenings, the mental and the physical. And, since my 

 perceptual powers, however aided, are such that I could not 

 perceive the link, therefore I cannot think in terms of it. 1 Never- 

 theless, this is not the main difficulty. It is merely part of the 

 larger difficulty raised by the idealist the difficulty of conceiving 

 how, even if material bodies exist, our minds, which are so 

 profoundly different from material objects, which do not occupy 

 space, and have none of the properties by means of which material 

 objects act and react on one another, can be affected by such 

 objects, can become aware of them. But, if we accept the common- 

 sense view, and suppose that material bodies both exist and affect 

 our minds, then, though we cannot conceive how the minds are 

 thus affected, it seems to me that we have no alternative but to 

 suppose that our minds are produced by our brains. As far as we 

 know, our minds are nothing other than streams of feelings, states 

 of consciousness. Ex hypothesi, some of these feelings symbolize 

 material objects. When we become aware of an object, that 

 object causes in the full sense of the word causes that feeling to 

 arise. But its action on the mind is not direct. It first produces 

 a change in a sense-organ. This change produces in turn a change 

 in a nerve, and that again a change in the brain. Thereupon we 

 become aware of the object. It follows, that if material objects 

 exist, and if our minds are aware of them, then our brains produce 

 in the full meaning of the word produce the feelings that symbolize 

 them. And, if it be admitted that they produce these items in the 

 stream of feelings, we have no grounds for denying that they pro- 

 duce any of the items, even the highest flights of thought. 



604. When we know the conditions exactly, we are able to 

 measure work in terms of the energy expended ; for example, we 

 are able to say that under certain conditions a certain expenditure 

 of energy will raise a certain mass a certain distance. We are 



1 See 573. 



