Internal

Internal Reflection occurs whenever a light ray strikes the surface of a medium whose refractive index is less than that of the medium in which the light is traveling. The amount of light that is reflected depends on the angle at which it hits the surface. Light from a point source (above) hits the surface at many angles. [pg. 44] [Light and Color, by Clarence Rainwater, Prof. of Physics, San Francisco State College, Original Project Editor Herbert S. Zim, Golden Press, NY, Western Publishing Company, Inc., 1971.]

Internal Tensions. The first four defining (delimiting) lines of a two-dimensional area are, in a sense, the first four lines of a design or composition. The internal tensions they inaugurate may, especially in the case of the Golden Section and root-5 rectangles, arouse optical interest without further partitioning. The energized blankness of these fields is arresting in and of itself. Yet these areas are seldom left vacant. More lines and shapes inscribed within them are capable of establishing other tension patterns that serve functional and a variety of esthetic purposes. Place even a point within a blank format, and horizontal and vertical divisions may be sensed immediately. These tensions, intersecting at the location of the intruding element, become the invisible governing lines of a composition. When developed further, they not only divide the composition into large and small two-dimensional areas, they also conjure fast and slow, up-down, side-to-side, diagonal, stepwise, and even circular movements on the surface and in depth.

Similar governing lines, spelled out three-dimensionally in proportion and scale, in form, space, and function, are seen in outstanding works of architecture. The architect, by the way he or she creates approaches, passageways, and cavities (wide and narrow, high and low, open and closed), more or less programs the movement of our eyes and bodies and influences both our sense of well-being and vital efficiency. [Harlan, Calvin. Vision & Invention, An Introduction to Art Fundamentals. Englewood Cliffs, NJ: Prentice-Hall, 1986.]

Internal/External aspects of Graduating Shape or Form.
Gradation of shape can be achieved by varying a form internally and/or externally

External without internal variation is achieved by adding to or subtracting from the form. Creating internal without external variations requires more prominent gradations. In most cases, shape gradations affect the external and internal aspects of a form. Any form can be changed to any other form with the appropriate number of shape gradations. [Wong, Wucius. Principals of Two-Dimensional Form. New York: Van Nostrand Reinhold Company, 1988.]

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Internalize vt [1884]: to give a subjective character to; specif: to incorporate [as values or patterns of culture] within the self as conscious or subconscious guiding principles through learning or socialization