Petr Nikolaevich Lebedev and his school (On the 120th anniversary of the year of his birth)
P. N. Lebedev is characterized as a scientist and a teacher. Results of his fundamental investigations in the fields of electromagnetic waves, light pressure, ultrasonics are described. P. N. Lebedev was the first to demonstrate experimentally the pressure of light on solids (1899--1901) and on gases (1907--1909). He developed new methods of generating and detecting millimeter electromagnetic waves and having obtained wavelengths of about 3 mm he laid the foundations of molecular ultrasonics. He is shown to have been a teacher of creative young people and a scientific leader who organized, in Moscow, the first school of physicists in our country. The principal results of the research by P. N. Lebedev's students during the time they worked with him are described.