55. Physical effects mediums are most particularly capable of inducing material phenomena, such as movements, raps, etc., with the aid of tables or other objects. When these phenomena express a thought or obey a will, they are intelligent effects, which for that very reason, point to an intelligent cause and are a way for spirits to manifest. By means of a. number of ordinary raps, we may receive answers such as yes or no, or die designation of letters of the alphabet that may be used to form words or sentences. This primitive method is very slow and does not lend itself to lengthy exchanges. Talking tables began the science; nowadays, there are means of communication that are as fast and complete as the ones used between incarnates; tables serve only incidentally and for experimentation.