The faculty is undoubtedly useful in a high degree to inventive mechanicians, and the great majority of those whom I have questioned have spoken of their powers as very considerable.  They invent their machines as they walk, and see them in height, breadth, and depth as real objects, and they can also see them in action.  In fact, a periodic action of any kind appears to be easily recalled.  But the powers of other men are considerably less; thus an engineer officer who has himself great power of visual memory, and who has superintended the mathematical education of cadets, doubts if one in ten can visualise an object in three dimensions.  I should have thought the faculty would be common among geometricians, but many of the highest seem able somehow to get on without much of it.  There is a curious dictum of Napoleon I. quoted in Hume’s Precis of Modern Tactics, p. 15, of which I can neither find the original authority nor do I fully understand the meaning.  He is reported to have said that “there are some who, from some physical or moral peculiarity of character, form a picture (tableau) of everything.  No matter what knowledge, intellect, courage, or good qualities they may have, these men are unfit to command.”  It is possible that “tableau” should be construed rather in the sense of a pictorial composition, which, like an epigrammatic sentence, may be very complete and effective, but not altogether true.

There can, however, be no doubt as to the utility of the visualising faculty when it is duly subordinated to the higher intellectual operations.  A visual image is the most perfect form of mental representation wherever the shape, position, and relations of objects in space are concerned.  It is of importance in every handicraft and profession where design is required.  The best workmen are those who visualise the whole of what they propose to do, before they take a tool in their hands.  The village smith and the carpenter who are employed on odd jobs employ it no less for their work than the mechanician, the engineer, and the architect.  The lady’s maid who arranges a new dress requires it for the same reason as the decorator employed on a palace, or the agent who lays out great estates.  Strategists, artists of all denominations, physicists who contrive new experiments, and in short all who do not follow routine, have need of it.  The pleasure its use can afford is immense.  I have many correspondents who say that the delight of recalling beautiful scenery and great works of art is the highest that they know; they carry whole picture galleries in their minds.  Our bookish and wordy education tends to repress this valuable gift of nature.  A faculty that is of importance in all technical and artistic occupations, that gives accuracy to our perceptions, and justness to our generalisations, is starved by lazy disuse, instead of being cultivated judiciously in such a way as will on the whole bring the best return.  I believe that a serious study of the best method of developing and utilising this faculty, without prejudice to the practice of abstract thought in symbols, is one of the many pressing desiderata in the yet unformed science of education.