Page:Popular Science Monthly Volume 18.djvu/75

Rh of the nerves, as in dreams, in delirium, in high excitement, or under the influence of certain drugs.

These physiological considerations, vague as they are, will nevertheless suffice to establish the existence of a true kinship between mental imagery and ordinary vision. They enable us to define Shakespeare's phrase of seeing "with the mind's eye" as a condition in which the activity of the nervous center bears a higher ratio to that of the nervous terminations than it does in actual sight. They also justify us in ascribing the marked differences in the quality, as well as the vividness, of the mental imagery of different persons, to the various degrees in which the several links of a long nervous chain are apt to be affected.

The mental images of which I am about to speak are those which are habitually suggested by well-known associations. Even when the subject is thus limited, it is almost too large for the compass of a single memoir. Therefore, I shall do my best at present not to encroach upon that other very interesting branch of it, which treats of the visions and hallucinations that flash into view without any connection with the subjects of conscious thought. It is my purpose to point out the conditions under which mental imagery as above defined is most useful, and the particular forms of it which we ought to aim at developing; and I shall adduce evidence to show that the visualizing faculty admits of being educated, although no attempt has ever yet been made, so far as I know, to bring it systematically and altogether under control.

I draw my conclusions from no small amount of testimony. In addition to a large quantity of oral information of which I have made notes, I have received separate letters and replies by the hundred to a long list of questions which I circulated, besides obtaining batches of replies to the same questions from various schools. The answers, on the whole, have been written in a style that testifies to much careful self-analysis, and the general accordance of those that were, derived from independent sources, together with the satisfactory way in which I have found many of the statements to bear cross-examination, has convinced me of their substantial truth.

I find the distribution of the visualizing faculty, in respect to its vividness, by a simple method I have described elsewhere. I take a haphazard bundle of returns, mark them as an examiner would mark the papers of candidates, sort them in the order of their marks, and clip them into a portfolio. If I open the book in the middle I read the medium value; if I open it at one quarter from the beginning I read the highest quartile value; if at one quarter from the end, the lowest quartile. If I open it at one eighth of its thickness I read an octile value; and if at one sixteenth, a sub-octile.