392 Mr. W. R. Browne on the 
the other reality in the physical universe — energy, which is 
never found un associated with matter, depends in all its widely 
varied forms upon motion of matter." 
Now I should have thought it an accepted principle in 
science that if a train of reasoning is found to lead to a con- 
clusion which not only has not been explained, but of which no 
explanation has been imagined — in other words, which is not 
only a mere unsupported hypothesis, but as to which no hypo- 
thesis can by the wit of man be framed — then that is sufficient 
reason for concluding, not that the unimaginable is inevitably 
true, but that the reasoning is inevitably false. It will be a bad 
day for science when its leaders forget the principle of which 
Newton was so brilliant an exponent — the principle, namely, 
of distrusting your conclusions the moment they are shown 
to be incompatible with ordinary matters of fact. But in the 
present case the particular flaw in the argument (apart from 
the general question at issue) is easily seen by an instance. 
Let us suppose a current of water (it is an ordinary case) run- 
ning through a fan water-meter, the disk of -which it keeps in 
rotation, and then passing by a pipe into a tank. When this 
is over, the quantity of water which has come to rest in the 
tank should be the same as that which has passed through the 
meter; but this will be indicated by the counter, i. e. by 
the number of revolutions which the disk of the meter has 
made in the time. Then, following Prof. Tait's reasoning 
we should say : — " It is impossible to conceive of a truly 
stationary mass of water whose magnitude should depend 
in any way on the number of revolutions of a meter; and 
therefore we are forced to the conclusion that the water in 
the tank must really be continually causing the revolution 
of a meter, though we cannot explain, or even imagine 
where the meter can be." To this it w T ould be sufficient to 
reply that the water was measured, not when it was at rest 
but when it was moving; and so we reply that what we have 
measured is not potential energy directly, but kinetic eneroy 
which was being transformed into or from potential energy 
as the case may be. It may be well to add that what we have 
measured does not of course give us the total potential energy 
existing in the body, any more than the meter would give the 
total quantity of water in the tank, supposing, for instance 
that this happened to be the sea. 
That the criticism of this paper may not be negative only I 
will indicate another line of attack on Prof. Tait's position 
which is of a positive character. We have seen that he 
recognises two distinct and independent realities as revealed 
