_Whether we attend to more than one thing at once._--Analogous to the question already discussed, is the inquiry whether the mind ever attends or can attend to more than one thing at one and the same time; as when I read an author, my attention meanwhile being directed to some other object than the train of thought presented by the page before me, so that at the end of a paragraph or a chapter I find that I have no idea of what I have been reading, and yet I have followed with the eye, and perhaps pronounced aloud, every word and line of the entire passage. To do this must have required some attention. Have I then the power of attending to two things at once? So, when the musician carelessly strikes up a familiar air while engaged in animated conversation, and when the equilibrist balances both his own body upon the rope, and also a number of bodies upon different parts of his body, each movement of each requiring constant and instant attention, the same question arises. _Opinion of Mr. Stewart._--Mr. Stewart, in accordance with the view already expressed of the rapidity of the mind's action, maintains that we do not under any circumstances attend at one and the same time to two objects of thought, but that the mind passes with such rapidity from one to another object in the cases supposed, that we are unconscious of the transition, and seem to ourselves to be attending to both objects at once. _Illustration of this View._--An illustration of this we find in the case of vision. Only one point of the surface of any external object is at any one instant in the direct line of vision, yet so rapidly does the eye pass from point to point, that we seem to perceive at a glance the whole surface. _How it is possible to compare different Objects._--It may be asked, How is it that we are able to compare one object with another, if we are unable to bring both before the mind at once? If, while I am thinking of A, I have no longer any thought whatever of B, how is it possible ever to bring together A and B before the mind so as to compare them? The answer I conceive to be this, that the mind passes with such rapidity from the one to the other object, as to produce the same effect that would be produced were both objects actually before it at the same instant. The transition is not usually a matter of consciousness; yet if any one will observe closely the action of his own mind in the exercise of comparison, he will detect the passing of his thoughts back and forth from one object to the other many times before the conclusion is reached, and the comparison is complete. CHAPTER III. CONCEPTION.