In order to prove what he terms the 'duality' of my mental constitution, Dr. Carpenter contrasts my researches on the Radiometer with some experiments I made six years ago when I attempted to solve the mystery of the phenomena called spiritual, and he describes the apparatus I devised to test the alteration of the weight of suspended bodies in Mr. Home's presence, by mere contact and without pressure. In a lecture delivered at Chelsea, on the 19th of January, 1872, Dr. Carpenter referred to this experiment: and whether his description was accurate will be seen by an extract from a letter by Mr. A. R. Wallace dated February 15, 1872:--

     In the report of Dr. Carpenter's lecture at Chelsea there occurs a passage so extraordinary and so entirely misleading that I must beg you, in the interests of truth, to allow me to make a few remarks upon it. Dr. Carpenter is stated to have said that he would grapple with Mr. Crookes's 'Psychic Force;' and, in attempting to do so, exhibited an experiment intending to show (and which his audience must have believed really did show) that Mr. Crookes was ignorant of the merest rudiments of mechanics, and was deluded by an experiment, the fallacy of which an intelligent schoolboy could have pointed out. Dr. Carpenter, it is said, exhibited a glass of water poised against an equal weight upon a balance, and showed that by dipping a finger in the water--that is, by pressing with a force exactly equal to the weight of the water displaced by the immersed finger--you increased the weight on that side of the balance. Now, unless the audience were intended to believe that Mr. Crookes was ignorant of this childishly simple fact, and, further, that it completely accounted for the result of his experiment, for what purpose was this experiment shown? Yet if this is what it was intended to prove, then it becomes absolutely certain that Dr. Carpenter could never have read Mr. Crookes's account of his experiments given in October last in the Quarterly Journal of Science (for he would certainly not wilfully misrepresent the experiment), and was therefore in complete ignorance of what he was attempting to disprove. For, will it be believed, Mr. Crookes expressly states that 'dipping the hand to the fullest extent into the water does not produce the least appreciable action on the balance,' the reason of which is sufficiently clear, for his woodcut shows, and his description tells us, that the vessel of water was not placed on the scale of a balance at all, but on a board exactly over its fulcrum or point of support at one end, while the distant end was suspended from a balance. Yet this balance showed a force of more than one pound exerted on it, when Mr. Home merely dipped the tips of the fingers of one hand in the water!