Dilatation and Conductivity
Certain other great changes, too, occur here.
We know that most materials expand uniformly upon heating and contract as they cool. Steel is no exception, but at the critical range on heating it becomes fickle and for a short space contracts instead of continuing its uniform expansion. Conversely, during cooling, it ceases its uniform contraction and suddenly dilates or expands for a short period when it reaches the critical range, after which aberration it again resumes its old habit of uniform contraction as the temperature falls.
Just so with its electrical conductivity. At the critical range the electrical conductivity suddenly decreases abnormally as the piece gets hotter and as abnormally increases as the steel cools through the critical range on the return trip.
There are certain other happenings at or near this particular temperature but we will not consider them here.
Manifestly all of this has a deep meaning.