"In scientific truth there is no finality, and there should therefore be no dogmatism. When this is forgotten, then science will become stagnant, and its high-priests will endeavour to strangle new learning at its birth."--R. A. GREGORY, _Discovery_. How does mind communicate with mind? Our accustomed process is singularly indirect. Speech is the initiation of muscular movements, under brain and nerve guidance, which result in the production of atmospheric pulsations--alternate condensations and rarefactions--which spread out in all directions in a way that can be likened superficially to the spreading of ripples on a pond. In themselves the aerial pulsations have no psychical connotation, and are as purely mechanical as are those ripples, though like the indentations on the wax of a phonograph their sequence is cunningly contrived; and it is in their sequence that the code lies--a code which anyone who has struggled with a foreign language knows is difficult to learn. Sound waves have in some respects a still closer analogy with the etherial pulsations generated at a wireless-telegraph sending station, which affect all sensitive receiving instruments within range and convey a code by their artificially induced sequence. Hearing is reception of a small modicum of the above aerial pulsations, by suitable mechanism which enables them to stimulate ingeniously contrived nerve-endings, and so at length to affect auditory centres in the brain, and to get translated into the same kind of consciousness as was responsible for the original utterance. The whole is done so quickly and easily, by the perfect physiological mechanism provided, that the indirect and surprising nature of the process is usually overlooked; as most things are when they have become familiar. Wireless telegraphy is not an iota more marvellous, but, being unfamiliar, it has aroused a sense of wonder. Writing and Reading by aid of black marks on a piece of paper, perceived by means of the Ether instead of the air, and through the agency of the eye instead of the ear,--though the symbols are ultimately to be interpreted as if heard,--hardly need elaboration in order to exhibit their curiously artificial and complicated indirectness: and in their case an element of delay, even a long time-interval--perhaps centuries--may intervene between production and reception.