Some laws of a system with a constant amount of energy

In this paper, different relationships and functional dependences of a system with a constant energy U=const., have been analyzed. The combinatorial nature of this analysis enables the conclusion that a family of entropy curves i.e. ? (N, U), for U = const, have an envelope. The envelope theory is very important for consideration of long & short range order of statistic thermodynamic systems. Since, we analyzed a system for U=const, we could explain some non-continual properties of a material. Like an example of this statement, we observed the situation, which is caused by anomaly filling of electronic orbits during the transfer from d to f elements.