of December, at 10.30 a.m. With these four cords I went to the neighbouring dwelling of one of my friends, who had offered to Mr. Henry Slade the hospitalities of his house, so as to place him exclusively at my own and my friend's disposition, and for the time withdrawing him from the public. The séance in question took place in my friends' sitting-room immediately after my arrival. I myself selected one of the four sealed cords, and, in order never to lose sight of it before we sat down at the table, I hung it around my neck-the seal in front always within my sight. During the séance, as previously stated, I constantly kept the seal-remaining unaltered-before me on the table. Mr. Slade's hands remained all the time in sight; with the left he often touched his forehead, complaining of painful sensations. The portion of the string hanging down rested on my lap,-out of my sight, it is true, but Mr. Slade's hands always remained visible to me. I particularly noticed that Mr. Slade's hands were not withdrawn or changed in position. He himself appeared to be perfectly passive, so that we cannot advance the assertion of his having tied those knots by his conscious will, but only that they, under these detailed circumstances, were formed in his presence without visible contact, and in a room illuminated by bright daylight.

According to the reports so far published the above experiment seems also to have succeeded in Vienna in presence of Mr. Slade, although under less stringent conditions.* Those of my readers who wish for further information on other physical phenomena which have taken place in Mr. Slade's presence, I refer to these two books. I reserve to later publication in my own treatises the description of further experiments obtained by me in twelve séances with Mr. Slade, and, as I am expressly authorised to mention, in the presence of my friends and colleagues, Prof. Fechner, Prof. Wilhelm Weber, the celebrated electrician from Göttingen, and Herr Scheibner, Professor of Mathematics in the University of Leipzig, who are perfectly convinced of the reality of the observed facts, altogether excluding imposture or prestidigitation.

At the end of my first treatise, already finished in manuscript in the course of August, 1877, I called attention to the circumstance that a certain number of physical phenomena, which, by "synthetical conclusions à priori," "might

* "Mr. Slade's Aufenshalt in Wien: Ein offener Brief an meine freunde." Wien: I. C. Fischer, and Co., 1878. "Der Individualismus im Lichte der Biologie und Philosophie der Gegenwart von Lazar B. Hellenbach." Wien: Braumüller, 1878.

be explained through the generalised conception of space and the platonic hypothesis of projection, coincided with so-called spiritualistic phenomena. Cautiously, however, I said:

"To those of my readers who are inclined to see in spiritualistic phenomena an empirical confirmation of those phenomena above deduced in regard to their theoretical possibility, I beg to observe that from the point of view of idealism there must first be given. a precise definition and criticism of objective reality. Indeed, if everything perceivable is a conception produced in us by unknown causes, the distinguishing characteristic of the objective reality from the subjective reality (phantasma) cannot be sought in nature, but only in accidental attributes of that process producing conceptions. If causes unknown to us produce simultaneously in several individuals the same conception, only subject to those distinctions which depend upon differences in the position of the observers, we refer such conception to a real object outside of us; this conception not taking place, we refer that conception to causes within us, and call it hallucination.

"Now, whether the spiritualistic phenomena belong to the first or to the second category of these conceptions, I do not venture to decide, so far never having witnessed such phenomena. On the other hand, I do not possess, with regard to men like Crookes, Wallace, and others, such an exalted opinion of my own intellect, as to believe that I myself, under similar conditions, should not be subject to the same impressions." (Written in August, 1877.)

This supposition received, four months after my writing it down, a full confirmation by the above-mentioned experiments with the American, Mr. Henry Slade. In making them I was intent upon giving full consideration to the above-cited distinction between a subjective phantasma and an objective fact. The four knots in the above-mentioned cord, with the seal unbroken, this day still lie before me; I can send this cord to any man for examination; I might send it by turn to all the learned societies of the world, so as to convince them that not a subjective phantasma is here in question but an objective and lasting effect produced in the material world, which no human intelligence with the conceptions of space so far current is able to explain.

If, nevertheless, the foundation of this fact, deduced by

me on the ground of an enlarged conception of space, should be denied, only one other kind of explanation would remain, arising from a moral mode of consideration that at present, it is true, is quite customary. This explanation would consist in the presumption that I myself and the honourable men and citizens of Leipzig, in whose presence several of these cords were sealed, were either common impostors or were not in possession of our sound senses sufficient to perceive if Mr. Slade himself, before the cords were sealed, had tied them in knots. The discussion, however, of such a hypothesis would no longer belong to the dominion of science, but would fall under the category of social decency.

Some other still more surprising experiments-prepared by me with a view to further testing this theory of space-have succeeded, though Mr. Slade thought their success impossible. The sympathising and intelligent reader will be able to understand my delight caused thereby. Mr. Slade produced on me and on my friends the impression of his being a gentleman: the sentence for imposture pronounced against him in London necessarily excited our moral sympathy, for the physical facts observed by us in so astonishing a variety, in his presence, negatived on every reasonable ground the supposition that he in one solitary case had taken refuge in wilful imposture. Mr. Slade, in our eyes, therefore, was innocently condemned-a victim of his accuser's and his judge's limited knowledge.

VII. LIQUEFACTION OF OXYGEN.*
By M. RAOUL PICTET.

HE object which I have had in view for more than three years is to demonstrate experimentally that molecular cohesion is a general property of bodies, to which there is no exception.

If the permanent gases are not capable of liquefying, we must conclude that their constituent particles do not attract each other, and thus do not conform to this law.

Thus, to cause experimentally the molecules of a gas to

The liquefaction of oxygen is so important a scientific achievement that we have much pleasure in laying before our readers the following detailed account of the means employed and diagrams of the apparatus used, which were communicated to us by M. Pictet himself.-ED. Q. 7. S.