intensity, when subjected to intense currents of electricity, or when subjected to high temperatures, or has by mechanical force been pushed together, or, as it is called, upset, becomes extremely crystalline. Under all of these circumstances it is subjected to one physical phenomenon, that of motion. It would seem that if a bar of iron were struck, the blow would shake the whole mass, and consequently the relative position of the particles remain unchanged, but this is not the case. When the blow is struck it takes an appreciable length of time for the effect to be communicated to the other end so as to be heard, if the distance is great. This shows that a small force is communicated from particle to particle independently along the whole mass, and that each atom actually moves independently of its neighbor. Then, if there be any attraction at the time tending to arrange it differently, it will conform to it. So much for theory with regard to this important matter. It looks well on paper, but do the facts of the case correspond? If practically demonstrated and systematically executed, experiments fail to corroborate the theory, and if, furthermore, we find there is no necessity for the theory, we naturally conclude that it is all wrong, or, at least, imperfectly understood. Now there is one other quality imparted to iron by successive shocks, which, I think, is independent of crystallization, and this quality is hardness and consequent brittleness. One noticeable feature about this also is, that as "absolute cohesion" or tensile strength diminishes, "relative cohesion" or strength to resist crushing increases. Specimens Nos. 2, 3, and 4 are pieces of Swedish iron, probably from the celebrated mines of Dannemora. Nos. 2 and 3 are parts of the same bolt, which, after some months' use on a "heading machine" in a bolt and nut works, where it was subjected to numerous and violent shocks, (perhaps 50,000 or 60,000 per day), it broke short off, as you see in No 2, showing a highly crystalline fracture. To test whether this structure continued through the bolt, I had it nicked by a blacksmith's cold chisel and broken. The specimen shows that it is still stronger at that point than at the point where it is actually broken, but the resulting fracture shows the same crystalline appearance. I next had specimen No. 4 cut from a fresh bar of iron which had never been used for anything. It also shows a crystalline fracture, indicating that this peculiarity had existed in the iron of both from the beginning.