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go up. I know that is stated, but I do not believe itr I must maintain, then, 
that the objections to my views of causation are not supported by any ob- 
servations with which Dr. M { Cann has favoured us. With regard to 
Mr. Moore, he says he speaks as a metaphysician, and not as a physicist. 
Now, I maintain that, in the discussion of physical questions, if metaphysics 
come into collision with the inexorable logic of facts, so much the worse for 
the metaphysics ; they must fall to the ground. 
Mr. Moore. — Oh, no. 
Mr. Brooke.— The world will be controlled by the inexorable logic of 
facts, and not by any metaphysical disquisition offered in opposition to the 
facts. 
Mr. Moore.— S o much the worse for the facts. 
Mr. Brooke. — Mr. Moore spoke of night as the cause of day. Now that 
is really an idea of causation which produces no impression at all upon my 
mind. 
The Chairman. — That was in reference to Mr. Mill. 
Mr. Brooke. — Well, at all events, it is not admissible. He laid a great 
deal of stress on atoms, and upon their nature. I have already stated 
that we know nothing of their nature. Again, he spoke of atoms subse- 
quently, and of colour being a property of atoms. There is no question 
about it, colour has nothing to do with atoms at all ; it is an impression 
produced upon the sensitive organs of the eye by vibratory motions of parti- 
cular periods. A vibratory motion, comprising a certain number of vibrations 
.in a second, produces upon the eye the impression of blue ; another number 
of vibrations in a second produces the sensation of yellow ; and another 
number produces the sensation of red. All this has nothing to do with atoms 
at all. Then Mr. Moore spoke of sound as motion, and asked why it was 
that we could not see a sound. For this very simple reason, that the vibratory 
motion which leads to the perception of sound is a vibratory motion of one 
character, while the vibratory motion which produces upon the eye the per- 
ception of light is a vibratory motion of a totally different character, and the 
reason why we cannot see a sound is that the vibratory motion which produces 
it is not capable of affecting the eye, and therefore of producing any sensation 
in the organs of vision : that is the simple explanation of the matter. Then Mr. 
Moore has quoted a remark of my own from the introductory chapter in the 
last edition of my “ Elements of Physics.” He should not have quoted that 
passage, for I have now expressly stated in this paper that I have modified 
some of the views I there expressed. Following the example of some of our 
most eminent physicists, I spoke of light and heat as not having a material 
existence, but as being modes of motion, and that is one of the expressions 
which I have in the present paper taken exception against, as being logically 
inaccurate. Having stated that, I do not think it is quite fair of Mr. Moore 
to quote that introduction to which I have referred, as in opposition to what 
I have stated in this paper, for that is one of the points upon which I have 
modified my views. I did not then see, as I do now, the force of the objec- 
tion to it, and which objection I have pointed out in this paper. Then I come 
