It is natural to suspect that both of the parallel sections of our curves have something to do with the same thing, and for convenience since we noticed that mysterious glow of the test piece just as the needle came to rest, we might call the particular point which lies just half way between the temperatures under discussion, the point of glow, or as the metallurgists call it, the “point of recalescence” and the range between these two temperatures the “critical range”. I suppose it would be difficult to explain this phenomenon of the test piece unless we imagine that as the critical range is reached some internal reaction of the steel causes it to spontaneously take on heat at the same temperature in the first place and give off the stored heat at the same temperature as the piece was being cooled down, and this heat caused it to glow as was noticed. Now if we were to experiment further with our piece while at the critical range, we would find certain other remarkable changes, one of the most noticeable of which is the loss of magnetism at and above the critical range. Irons and steels are usually the most magnetic materials, but the attraction of the magnet is completely lost at or above the critical range. We can easily satisfy ourselves in this respect by noting the attraction of a simple horse shoe magnet when our piece of test steel is brought into its magnetic field. As the pyrometer needle passes on up through the range of temperatures noted above, the magnetic attraction is perfectly evident when suddenly the recalescence point is reached, the spell is broken and the magnet and the test piece fall apart. But let us just consider this phenomenon a moment. We are told by the physicists that magnetism is induced in a piece of iron or steel by a “rearrangement of the internal molecular structure, in which the positive ions face one direction and the negative ions in the opposite direction”. Therefore, if magnetism suddenly ceases to exist it would seem as if something had happened to the “internal molecular structure” of the test piece. Thus when the recalescence point is reached we may conclude that something more than a mere absorption of heat units has taken place. In fact we may really believe that an actual internal molecular revolution has occurred and that some of the natural laws which formerly had governed all of these little molecules which go to make up the whole piece of steel, have been overthrown and that the molecules are more or less free to set up a new form of government for themselves, and that, therefore, when a piece of steel is brought to the recalescence point it is really in a very sensitive condition. In fact, if we should care to investigate further we should find that certain other great changes take place at this critical point, such, for instance, as partial failure of the test piece to conduct an electric current, which formerly, of course, it did with great ease.