837. As soon as I had introduced the serrated conductor, my spirit father corroborated the impression that it promoted the influence of the medium. 838. This was the first instance in which I have discovered any analogy between the laws governing the communication of the medium of the spirit will-power, and those obeyed by electrical phenomena. 839. An account is given in my narrative of an experiment in which a board, suspended at one end from a spring-balance, was made to descend with a force of three pounds, through the instrumentality of a medium who had no connection with the board, excepting water which was interposed. Hence, as the hook screwed into the board, by which it was secured to the hook of the balance, was six times as far from the fulcrum as the hands of the medium, the force exerted by the officiating spirit was equal to 3 × 6 = 18 pounds. (See Plate 3, and description.) Nevertheless, no upward reaction was perceptible to me, nor was any experienced by the medium, Henry Gordon, as he declared. 840. In the case of the boy (Plate 3,) a downward action of seven pounds was observed, which, multiplied by the difference of distance, amounted to 7 × 6 = 42 pounds, and yet the boy was not perceptibly impelled in the opposite direction. Nor, when through the same juvenile mediumship, the whole of the apparatus was thrown upon the floor, did the boy appear to be impelled in the opposite direction. Nor was there any reaction when the apparatus was thrown down. Now, agreeably to the laws of nature, as established by human experience, in all cases of motion or momentum, there must be an equal force exercised in the opposite direction by the _vis inertiæ_ of some other matter endowed with that attribute. Hence Archimedes said, “Give me but where to stand, and I will move the world.” A point of support, a place of resistance, however, was held to be indispensable. 841. The only explanation of which I can conceive is, that spirits, by volition, can deprive bodies of _vis inertiæ_, and move bodies, as they do themselves, by their will. But the necessity of the presence of a medium to the display of this power, granting its existence, is a mystery. 842. That the spirit should, by its “magic” will-power, take possession of the frame of a human being, so as to make use of its brain and nervous system, depriving its appropriate owner of control, is a wonderful fact sufficiently difficult to believe, yet, nevertheless, intelligible. The aura which surrounds a medium must be imponderable. No volition of the medium can, through its instrumentality, move ponderable bodies, nor cause raps or consequent vibrations in the wooden boards. Hence, the presence of a medium imparts power to spirits which the medium does not possess.