Tyndall has aptly stated the importance of visualizing one's ideas and particular concepts, as follows: "How, for example, are we to lay hold of the physical basis of light since, like that of life itself, it lies entirely without the domain of the senses?... Bring your imaginations once more into play and figure a series of sound-waves passing through air. Follow them up to their origin, and what do you there find? A definite, tangible, vibrating body. It may be the vocal chords of a human being, it may be an organ-pipe, or it may be a stretched string. Follow in the same manner a train of ether waves to their source, remembering at the same time that your ether is matter, dense, elastic and capable of motions subject to and determined by mechanical laws. What then do you expect to find as the source of a series of ether waves? Ask your imagination if it will accept a vibrating multiple proportion--a numerical ratio in a state of oscillation? I do not think it will. You cannot crown the edifice by this abstraction. The scientific imagination which is here authoritative, demands as the origin and cause of a series of ether waves a particle of vibrating matter quite as definite, though it may be excessively minute, as that which gives origin to a musical sound. Such a particle we name an atom or a molecule. I think the seeking intellect, when focused so as to give definition without penumbral haze, is sure to realize this image at the last." By repeatedly exercising the faculty of Imagination upon a particular idea, we add power and clearness to that idea. This is but another example of the familiar psychological principle expressed by Carpenter as follows: "The continued concentration of attention upon a certain idea gives it a dominant power." Kay says: "Clearness and accuracy of image is only to be obtained by repeatedly having it in the mind, or by repeated action of the faculty. Each repeated act of any of the faculties renders the mental image of it more clear and accurate than the preceding, and in proportion to the clearness and accuracy of the image will the act itself be performed easily, readily, skillfully. The course to be pursued, the point to be gained, the amount of effort to be put forth, become more and more clear to the mind. It is only from what we have done that we are able to judge what we can do, and understand how it is to be effected. When our ideas or conceptions of what we can do are not based on experience, they become fruitful sources of error."