Before the first ball, which you will, perhaps more easily remember by the name, A, arrived so very near to the second ball B, as to have come within the sphere of their mutual repulsion, this second ball was at rest, that is to say, it had no tendency to move in any direction. This state of rest, however, is only one of the many states, in which a body may exist; and if, which must surely be allowed, a body having a tendency to continued motion, be in a different state, from one which has no such tendency, this change of state implying, it must be remarked, not even the slightest loss of identity, has been produced in the body B, by the mere vicinity of the body A. For the sake of illustration, let us now suppose this body A to be hot or luminous. It will still, as before, produce the new state of tendency to motion, in B, when it arrives within the limits of their sphere of repulsion. Is it less conceivable, then, that the mere presence of this hot or luminous body should produce the new sensation of warmth, or of colour, which are different states of the sentient mind, without affecting in the slightest degree the identity of the mind itself, than that it should produce, without any loss of absolute identity, in the body B, an immediate tendency, in that body, to move along with a certain velocity, a state as different from that in which it remains at rest, as the sensation of warmth, which is one state of the mind, is different from the sensation of colour, which is another state of the mind? Nor does the parallel end here; for, since a body at rest, acquiring a tendency to begin motion in one particular direction, as, for example, to move _north_, must be in a different state from that in which it would have been, if it had acquired an instant tendency to move _east_, or in any other direction; and, the direction once begun, being the same, since a body having a tendency to move with one velocity, must, at every moment of its progress, be in a different state from that in which it has a tendency to move with a different velocity, it is evident, that the mere presence of a body may produce, in a second body, according to the difference of their positions and relative magnitudes, a variety of states, that, when all the varieties of direction, and all the varieties of velocity are estimated together, may be considered as infinite,--equal at least in number, to the different states of which the mind is susceptible, in its almost infinite variety of feelings; and all this without any essential change, that can affect the identity of the quiescent or moving body, or any essential change, that can affect the identity of the mind.