Usually each definite thought creates a new thought-form; but if a thought-form of the same nature is already hovering round the thinker, under certain circumstances a new thought on the same subject, instead of creating a new form, coalesces with and strengthens the old one, so that by long brooding over the same subject a man may sometimes create a thought-form of tremendous power. If the thought be an evil one, such a thought-form may become a veritable malign influence lasting perhaps for many years, and having for a time all the appearance and powers of a real living entity. A shell of self-centred thought obviously must tend to obscure the mental vision and facilitate the formation of prejudice.
Through such a shell the man looks out upon the world, naturally seeing everything tinged with its predominant colours; everything which reaches him from without is thus more or less modified by the character of the shell. Thus, until a man has complete control of thought and feeling, he sees nothing as it really is, since all his observations must be made through this medium which, like a badly-made glass, distorts and colours everything. It was for this reason that Aryasangha [now the Master Djwal Kul] said in The Voice of the Silence that the mind was “the great slayer of the real”. He was drawing attention to the fact that we do not see any object as it is, but only the images that we are able to make of it, everything being thus necessarily coloured for us by these thought-forms of our own creation.
If a man’s thought of another is merely contemplative and involves no feeling [such as affection or dislike], or desire [such as a wish to see the person] the thought does not usually perceptibly affect the man whom he thinks. If, however, there is feeling, eg., affection, associated with the thought, the thought-form, built out of matter of the thinker’s mental body, and this astro-mental form leaps out of the body in which it has been generated, goes straight towards the object of the feeling, and fastens itself upon him. It may be compared to a Leyden jar; the form of elemental essence corresponds to the Leyden jar, and the thought energy to the charge of electricity.
If the man is at the moment in a passive condition, or if he has within him active vibrations of a character harmonious with those of the thought-form, the thought-form will at once discharge itself upon him, and in the act cease to exist. The effect is to provoke a vibration similar to its own, if none such already exists; or to intensify it if it is already to be found there. If the man’s mind is so strongly occupied along other lines that it is impossible for the vibration to find an entrance, the thought-form hovers about him waiting for an opportunity to discharge itself. A thought-form sent from one person to another thus involves the actual transference of a certain amount both of force and of matter from the sender to the recipient.
***From Arthur E. Powell – The Mental Body