orders, and it moved in alliance with different faculties; but this Vision was the cardinal quality of both.  Dr. Johnson was guilty of a surprising fallacy in saying that a great mathematician might also be a great poet:  “Sir, a man can walk east as far as he can walk west.”  True, but mathematics and poetry do not differ as east and west; and he would hardly assert that a man who could walk twenty miles could therefore swim that distance.

The real state of the case is somewhat obscured by our observing that many men of science, and some even eminent as teachers and reporters, display but slender claims to any unusual vigour of imagination.  It must be owned that they are often slightly dull; and in matters of Art are not unfrequently blockheads.  Nay, they would themselves repel it as a slight if the epithet “imaginative” were applied to them; it would seem to impugn their gravity, to cast doubts upon their accuracy.  But such men are the cisterns, not the fountains, of Science.  They rely upon the knowledge already organised; they do not bring accessions to the common stock.  They are not investigators, but imitators; they are not discoverers—­inventors.  No man ever made a discovery (he may have stumbled on one) without the exercise of as much imagination as, employed in another direction and in alliance with other faculties, would have gone to the creation of a poem.  Every one who has seriously investigated a novel question, who has really interrogated Nature with a view to a distinct answer, will bear me out in saying that it requires intense and sustained effort of imagination.  The relations of sequence among the phenomena must be seen; they are hidden; they can only be seen mentally; a thousand suggestions rise before the mind, but they are recognised as old suggestions, or as inadequate to reveal what is sought; the experiments by which the problem may be solved have to be imagined; and to imagine a good experiment is as difficult as to invent a good fable, for we must have distinctly present—­clear mental vision—­the known qualities and relations of all the objects, and must see what will be the effect of introducing some new qualifying agent.  If any one thinks this is easy, let him try it:  the trial will teach him a lesson respecting the methods of intellectual activity not without its use.  Easy enough, indeed, is the ordinary practice of experiment, which is either a mere repetition or variation of experiments already devised (as ordinary story-tellers re-tell the stories of others), or else a haphazard, blundering way of bringing phenomena together, to see what will happen.  To invent is another process.  The discoverer and the poet are inventors; and they are so because their mental vision detects the unapparent, unsuspected facts, almost as vividly as ocular vision rests on the apparent and familiar.