symmetrically arranged, had predicted (in 1827) that a portion of such a substance would, when brought into the neighbourhood of a magnet, act differently, according to the different positions in which it might be turned about its centre. But this very inability to follow Poisson’s refined analysis gave a new direction to Faraday’s thoughts, and caused him to conceive the idea of magnetic permeabilities differing in different directions, an idea which, as Sir William Thomson (the present Lord Kelvin) showed in 1851,[53] is equally susceptible of mathematical treatment by appropriate symbols. Lord Kelvin has also spoken (_op. cit._, p. 484) of the matter as follows: “The singular combination of mathematical acuteness with experimental research and profound physical speculation which Faraday, though not a ‘mathematician,’ presented is remarkably illustrated by his use of the expression ‘_conducting power of a magnetic medium for lines of force_.’” Tyndall has given a succinct summary of these researches--in which also he took a part--from which the following extract must suffice:-- And here follows one of those expressions which characterise the conceptions of Faraday in regard to force generally: “It appears to me impossible to conceive of the results in any other way than by a mutual reaction of the magnetic force, and the force of the particles of the crystal upon each other.” He proves that the action of the force, though thus molecular, is an action at a distance. He shows that a bismuth crystal can cause a freely-suspended magnetic needle to set parallel to its magnecrystallic axis. Few living men are aware of the difficulty of obtaining results like this, or of the delicacy necessary to their attainment. “But though it thus takes up the character of a force acting at a distance, still it is due to that power of the particles which makes them cohere in regular order and gives the mass its crystalline aggregation, and so often spoken of as acting at _insensible_ distances.” Thus he broods over this new force, and looks at it from all points of inspection. Experiment follows experiment, as thought follows thought. He will not relinquish the subject as long as a hope exists of throwing more light upon it. He knows full well the anomalous nature of the conclusion to which his experiments lead him. But experiment to him is final, and he will not shrink from the conclusion. “This force,” he says, “appears to me to be very strange and striking in its character. It is not polar, for there is no attraction or repulsion.” And then, as if startled by his own utterance, he asks: “What is the nature of the mechanical force which turns the crystal round and makes it affect a magnet?”... “I do not remember,” he continues, “heretofore such a case of force as the present one--where a body is brought into position only without attraction or