original impulse of the balls, or to a series of such impulses.  We cannot predict what particular new variation will occur from any observation of the past.  Just as the first impulse was given to the balls at a point out of sight, so the impulse which resulted in the variety or new form was given at a point beyond observation, and is equally mysterious or unaccountable, except on the supposition of an ordaining will.  The parent had not the peculiarity of the variety, the progeny has.  Between the two is the dim or obscure region of the formation of a new individual, in some unknown part of which, and in some wholly unknown way, the difference is intercalated.  To introduce necessity here is gratuitous and unscientific; but here you must have it to make your argument valid.

I agree that, judging from the past, it is not improbable that variation itself may be hereafter shown to result from physical causes.  When it is so shown, you may extend your necessity into this region, but not till then.  But the whole course of scientific discovery goes to assure us that the discovery of the cause of variation will be only a resolution of variation into two factors:  one, the immediate secondary cause of the changes, which so far explains them; the other an unresolved or unexplained phenomenon, which will then stand just where the product, variation, stands now, only that it will be one step nearer to the efficient cause.  This line of argument appears to me so convincing, that I am bound to suppose that it does not meet your case.  Although you introduced players to illustrate what design is, it is probable that you did not intend, and would not accept, the parallel which your supposed case suggested.  When you declare that the proof of design in the eye and the hand, as given by Paley and Bell, was convincing, you mean, of course, that it was convincing, so long as the question was between design and chance, but that now another alternative is offered, one which obviates the force of those arguments, and may account for the actual results without design.  I do not clearly apprehend this third alternative.

Will you be so good, then, as to state the grounds upon which you conclude that the supposed proof of design from the eye, or the hand, as it stood before Darwin’s theory was promulgated, would be invalidated by the admission of this new theory?

D.T.—­As I have ever found you, in controversy, meeting the array of your opponent fairly and directly, without any attempt to strike the body of his argument through an unguarded joint in the phraseology, I was somewhat surprised at the course taken in your answer to my statement on Darwin’s theory.  You there seem to suppose that I instanced the action of the billiard balls and players as a parallel, throughout, to the formation of the organic world.  Had it occurred to me that such an application might be supposed to follow legitimately from my introduction of this action, I should certainly have stated that I did