that is those which are not confined to a particular spot in the circumference of the brain, but affect the general principle of thought, whatever this may be, whether composed of extended, material parts, or indivisible. Now if these secondary or conscious ideas, which we may represent as continually posting backwards and forwards like couriers in all directions through all quarters of the brain to meet each other and exchange accounts, are in fact the only instruments of association, it is plain that the account given by Hartley of that principle falls to the ground at once; first, because that account affords no explanation of any of the associations which take place in the mind, except when there is an immediate communication between the primary seats of the associated ideas; secondly, because these secondary or conscious ideas, being spread over the whole brain, or rather being impressed on the same thinking principle, cannot have any particular connection with or power to call up one another, or the contrary, from any circumstances of local distinction, which is thus completely done away with.
The doctrine of vibrations supposes the order of place and the order of time to correspond exactly in all combinations of our ideas, and that it is owing to this circumstance entirely that those ideas which have been impressed nearly at the same time have afterwards a power to call up one another from the facility with which they must be supposed to pass from their own primary seats into the contiguous ones of the associated ideas. I have endeavoured to shew on the contrary not only that there is no regular local arrangement of our ideas making them correspond exactly with the order in which they cohere together in the mind, but that there appears to be no distinction whatever in this respect; that they all belong absolutely to the same place or internal seat of conciousness; that this want of distinction is an evident fact
