life may help to make this important branch of our subject clearer, if we are careful not to push the analogy further than it will hold good. It is well known that if one of the wires of a harp be made to vibrate vigorously, its movement will call forth sympathetic vibrations in the corresponding strings of any number of harps placed round it, if they are tuned to exactly the same pitch. It is also well known that when a large body of soldiers crosses a suspension bridge it is necessary for them to break step, since the perfect regularity of their ordinary march would set up a vibration in the bridge which would be intensified by every step they took, until the point of resistance of the iron was passed, when the whole structure would fly to pieces. With these two analogies in our minds (never forgetting that they are only partial ones) it may seem more comprehensible that one who knows exactly at what rate to start his vibrations--knows, so to speak, the keynote of the class of matter he wishes to affect--should be able by sounding that keynote to call forth an immense number of sympathetic vibrations. When this is done on the physical plane no additional energy is developed; but on the astral plane there is this difference, that the matter with which we are dealing is far less inert, and so when called into action by these sympathetic vibrations it adds its own living force to the original impulse, which may thus be multiplied many-fold; and then by further rhythmic repetition of the original impulse, as in the case of the soldiers marching over the bridge, the vibrations may be so intensified that the result is out of all apparent proportion to the cause. Indeed, it may be said that there is scarcely any limit to the conceivable achievements of this force in the hands of a great Adept Who fully comprehends its possibilities; for the very building of the Universe itself was but the result of the vibrations set up by the Spoken Word. [Sidenote: Mantras.] The class of mantras or spells which produce their result not by controlling some elemental, but merely by the repetition of certain sounds, also depend for their efficacy upon this action of sympathetic vibration. [Sidenote: Disintegration.]