Another peculiar phenomenon of the astral plane, perceived by clairvoyants of a certain degree of development, is that which is known as the "thought-form." A thought-form is a specialized grouping of astral substance, crystalized by the strong thought impulses or vibrations of a person thinking, or manifesting strong emotional excitement. It is generated in the aura of the person, in the first place, but is then thrown off or emitted from the atmosphere of the person, and is sent off into space. A thought-form is really but a strongly manifested thought or feeling which has taken form in the astral substance. Its power and duration depend upon the degree of force of the thought or feeling manifesting it. These thought-forms differ very materially from one another in form and general appearance. The most common form is that of a tiny series of waves, similar to those caused by the dropping of a pebble in a pond of water. Sometimes the thought-form takes on the appearance of a whirlpool, rotating around a centre, and moving through space as well. Another form is like that of the pin-wheel fireworks, swirling away from its centre as it moves through space. Still another form is that of a whirling ring, like that emitted from a smokestack of a locomotive, or the mouth of a smoker--the familiar "ring" of the smoker. Others have the form and appearance of semi-luminous globes, glowing like a giant opal. Other thought-forms are emitted in jet-like streams, like steam puffed out from a tea-kettle. Again, it will appear as a series of short puffs of steam-like appearance. Again, it will twist along like an eel or snake. Another time it will twist its way like a corkscrew. At other times it will appear as a bomb, or series of bombs projected from the aura of the thinker. Sometimes, as in the case of a vigorous thinker or speaker, these thought-form bombs will be seen to explode when they reach the aura of the person addressed or thought of. Other forms appear like nebulous things resembling an octopus, whose twining tentacles twist around the person to whom they are directed. Each thought-form bears the same color that it possessed when generated in the aura of its creator, though the colors seem to fade with time. Many of them glow with a dull phosphorescence, instead of bright coloring. The atmosphere of every person, and every place, is filled with various thought-forms emanated from the person, or persons who inhabit the place. Each building has its own distinctive thought-forms, which permeate its mental atmosphere, and which are clearly discernible by trained clairvoyant vision.