**
**It analyses the derivation of the Langevin formula. A simple assumption in it is shown to be incorrect. It suggests a more accurate derivation of a related formula.

**Author(s) Details**

**Alexander A. Sobko
**Prokhorov Academy of Engineering Sciences, Moscow, 123557, Russia.

View Book :- https://bp.bookpi.org/index.php/bpi/catalog/book/319