But again it suddenly stops and remains immovable, or perhaps even rises slightly, for a period of several seconds, after which it resumes its uniformly-timed downward course as though nothing had happened. Yes, these pauses of the needle occurred at very nearly the same marking on the pyrometer dial, but not at exactly the same ones. Going up it was at 1350° F., and on the downward way it was at 1250° F. And you are correct in surmising that these two points are closely related. They are parts of the same, if we may so speak, and, in reality they represent one point which is located about halfway between them, the divergence resulting from what is known as “hysteresis” or “lag,” which means, of course, a “being-behind-hand” or tardiness. For the present we may say that all carbon steels have this “critical” range as shown by such pauses of the pyrometer needle during heating or cooling of the steel. Now as the piece is most certainly continuing to absorb heat in the furnace as it grows hotter and is losing it uniformly to the air as the furnace cools, we have no alternative but to judge that the pause of the needle on its upward way was caused by some internal affair of the piece of steel itself, for which, at just that stage of its journey, it required and used for its purpose (which was other than making itself hotter), the heat furnished it by the furnace; and, that on the downward journey, at just that same point, it gave out again that same heat. It must have been the setting free of this imprisoned heat, if we may so term it, which kept the piece for those few moments from cooling at the usual rate. Indeed, had we conducted our experiment in a rather dark room and observed the piece closely we would have noticed that during the pause of the pyrometer the piece of steel did brighten or glow somewhat, showing that it had extra heat from some hidden source. Because of this “self-heating” of the steel as shown by the pyrometer and the brightening, the temperature at which the phenomenon occurs has been named the “point of recalescence,” which means the point at which it spontaneously becomes hotter. Loss of Magnetism Now another curious thing took place had we but noticed it. We all know that iron and steel are our most magnetic materials. From childhood we have seen pins, needles, steel pens, and various other steel or iron objects jump to a magnet held near them. What, now, when we find that our piece of steel in the furnace when at a red or higher heat is entirely unresponsive or dead to the attraction of a strong magnet? Strange! Do you suppose that our magnet has lost its power? Let us see. Suppose that every minute or so, while watching the pyrometer needle go slowly down again after turning off the heat, we put the magnet to the steel.