Mr. Alfred R. Wallace writes to us: "In your article on this subject, you appear to have been led into an error by Dr. Carpenter's constant habit of giving only one side of the question, and completely ignoring all facts which tell against his theory. You say, speaking of Reichenbach, 'But he did not try secretly removing the magnets, and then asking the sensitives whether they still saw the flames.' Now, every one who has read Reichenbach's book must know that tests of this kind were applied by him again and again, in an endless variety of ways. The magnets were continually changed in number, size, and position, in the totally dark chamber, and more than this, the magnet was sometimes completely hidden by a screen, but a lens was so placed as to throw the image of it (had there been light) on the wall. In every case, the sensitives described the flames from the magnet as small or large, single, double, or treble, high or low, to the right or to the left, just as the magnets were changed; and when the lens was used they described the flame on the wall, and were then asked to place their finger on it, when Reichenbach marked the place with a pencil, and found afterwards that the mark was exactly where the image would be thrown by the lens. Now, the negative fact, that in some cases mesmeric patients can be made to see anything by 'expectation,' does not disprove these cases in which all expectation was carefully excluded. Again, as to mesmerism at a distance unknown to the patient, Dr. Carpenter gives cases in which this failed, and in which the patient was mesmerised merely by the expectation of being so. This is one side--the negative side--of the question. But Dr. Carpenter knows that there is a positive side, which he ignores, of cases in which mesmerism has been produced when the patient did not and could not know he was being mesmerised. One of these is given by Professor Gregory's "Letters on Animal Magnetism," page 107, which happened in his own house to a member of his own family; and, to show the kind of evidence that Dr. Carpenter carefully omits to allude to, I hope you will allow me space briefly to state the facts. In Professor Gregory's house one evening this lady was mesmerised by a Mr. Lewis. Next morning at breakfast the lady complained of a headache. After his lecture Professor Gregory met Mr. Lewis, and told him that the lady he had mesmerised had a bad headache, to which Mr. Lewis replied that he would think of it some time during the day and mesmerise her so as to remove the headache. Professor Gregory did not return home till 5 o'clock, when, without being asked, the lady at once said to him that she had been mesmerised while nobody was present and while playing the piano, at half-past three o'clock. Her arms lost their power, and she was obliged to lie down and go into a short mesmeric sleep, and when she awoke her headache was gone. In the evening Professor Gregory met Mr. Lewis again; and was told that he had mesmerised the lady, as promised, as soon as he could get home to his lodgings, which was about half-past 3. The distance between the two houses was about a third of a mile; and the whole of the circumstances were such as to render 'expectation' out of the question. Dr. Carpenter continually compares the evidence for the facts of clairvoyance and spiritualism with that for the facts of science, to the disadvantage of the former. May I ask if it is the 'scientific' method of inquiry, to ignore facts which tell against you, and, while making much of negative evidence in your favour, to lead the public to suppose that there is no positive evidence on the other side? In the matter of the divining rod, I could adduce equally good and positive testimony against the lecturer's negative facts, but the above is sufficient to prove that whoever wishes to know the whole truth on this matter must not rely on the statements of Dr. Carpenter."