Mr. Alfred R. Wallace, President of the Entomological Society, has favoured us with the following copy of a letter sent to the Daily Telegraph, but not published by that journal:--

     Sir,--In the report of Dr. Carpenter's lecture at Chelsea (given in your issue of Saturday last), 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' "Psychic Force;" and, in attempting to do so, exhibited an experiment intended 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! Dr. Carpenter is an "eminent man of science" and a fellow of the Royal Society; yet if your reporter has correctly stated his mode of criticising the experiments of another F.R.S., we may be excused for not placing implicit confidence in the "two eminent men of science," who are said by Dr. Carpenter to have reported Mr. Crookes's facts "good for nothing."

Alfred R. Wallace.