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separated from each other. He then refers to a sentence in the discussion 
at the end of the paper, in which it appears that I spoke of force as being an 
attraction or a repulsion — a push or a pull. Now what I meant to say, and 
what I thought I said, was, that force was attractive or repulsive, and that 
it produces either a push or a pull ; that is to say, that a push or a pull is 
the result of a force, but is not a force itself. If I did say what is attributed 
to me in the report, it was an oversight. I am sorry that I have detained 
you so long ; but I felt, in justice to myself, that I was bound to show I was 
not guilty of the errors imputed to me. (Cheers.) 
Mr. E. Pickersgill. — I should like to refer to a few particulars in 
which it appears to me that Professor Birks has been a little unjust to the 
author of First Principles, who is the chief exponent of those Neo-Lucretian 
views which the Professor has attacked. In the first place, with regard to 
that expression, “ the persistence of force,” which Professor Tyndall and 
Mr. Herbert Spencer have used 
Professor Birks. — And Professor Huxley. 
Mr. Pickersgill. — It appears to me that, in being so severe upon that 
expression (he says it reminds him of the proverbial broomstick), Professor 
Birks has confined himself to that position of orthodoxy which is cer- 
tainly the position of myself, and which, I suppose, is the position of the 
majority in this room. But it seems to me that he ought, for the time at 
least, to have transferred himself into the position of Professor Tyndall and 
Mr. Herbert Spencer. “ The persistence of force ” may be a very terrible 
expression to orthodox thinkers, but to thinkers who are not orthodox — such 
as those to whom I have alluded — I do not see that it is terrible at all, and 
it appears to express very fairly that idea which Herbert Spencer intends in 
his First Principles. Then I take this passage from the paper : — 
“ Is the total of force, in such a universe, fixed, constant, and invariable ? 
It is one of the simplest truths of dynamics that it varies continually, 
from hour to hour, from moment to moment. If attractive forces are in 
excess, it increases in a condensing system, and decreases with dilatation.” 
Let us consider the conditions of the material world as proposed in this 
paper. It consists of a vast — not infinite — number of atoms, between some 
of which there is exercised an attractive force, and between some of which 
there is exercised a repulsive force. Now, suppose the attractive forces are 
in excess, and that the system is condensed. Now, it is perfectly true that, 
upon the condensation of that system, the total sum of attractive forces 
will be increased ; but is it not equally true that the total sum of 
the repulsive forces will be diminished, and therefore that the dif- 
ference between them, i. e. the net total of force, may remain precisely 
as it was before the condensation ? There are one or two other points 
to which I should like to call your attention. Professor Birks says : — 
“ Yet we are taught that this wholly unknown Being, whether ho 
has a will to do it or not, cannot destroy one particle of this wholly un- 
known and unknowable thing or quality, which we call Force or Energy.” 
Now, Mr. Herbert Spencer does not suppose the existence of an un- 
