Light Waves and Their Uses
forms and combinations of forms which are encountered at every turn.
Indeed, so strongly do these color phenomena appeal to me that I venture to predict that in the not very distant future there may be a color art analogous to the art of sound — a color music, in which the performer, seated before a literally chromatic scale, can play the colors of the spectrum in any succession or combination, flashing on a screen all possible gradations of color, simultaneously or in any desired succession, producing at will the most delicate and subtle modulations of light and color, or the most gorgeous and startling contrasts and color chords! It seems to me that we have here at least as great a possibility of rendering all the fancies, moods, and emotions of the human mind as in the older art.
These beauties of form and color, so constantly recurring in the varied phenomena of refraction, diffraction, and interference, are, however, only incidentals; and, though a never-failing source of aesthetic delight, must be resolutely ignored if we would perceive the still higher beauties which appeal to the mind, not directly through the senses, but through the reasoning faculty; for what can surpass in beauty the wonderful adaptation of Nature’s means to her ends, and the never-failing rule of law and order which governs even the most apparently irregular and complicated of her manifestations? These laws it is the object of the scientific investigator to discover and apply. In such successful investigation consists at once his keenest delight as well as his highest reward.
It is my purpose to bring before you in the following lectures an outline of a number of investigations which are based on the use of light waves. I trust I may be pardoned for citing, as illustrations of these uses, examples which are taken almost entirely from my own work. I do this because
Wave Motion and Interference
I believe that I shall be much more likely to interest you by telling what I know, than by repeating what someone else knows.
In order to discuss intelligently these applications of light waves, it will be necessary to recall some fundamental facts about light and especially about wave motion. These facts, though doubtless familiar to most of us here, need emphasis and illustration in order that we may avoid, as far as possible, the tedious repetition against which we were warned.
Doubtless there are but few who have not watched with interest the circular waves produced by a stone cast into a still pond of water, the ever-widening circles, going farther and farther from the center of disturbance, until they are lost in the distance or break on the shore. Even if we had no knowledge of the original disturbance, its character, in a general way, might be correctly inferred from the waves. For instance, the direction and distance of the source can be determined with considerable accuracy by drawing two lines perpendicular to the front of the wave; the source would lie at their intersection. The size of the waves will give information concerning the size of the object thrown. If the waves continue to beat regularly on the shore, the disturbance is continuous and regular; and, if regular, the frequency (/. <?», the number of waves per second) determines whether the disturbance is due to the splash of oars, to the paddles of a steamer, or to the wings of an insect struggling to escape.
In a precisely similar manner, though usually without conscious reasoning about the matter on our part, the sound waves which reach the ear give information regarding the source of the sound. Such information may be classified as follows:
1. Direction (not precise).
2. Magnitude (loudness).