Second Knee in Cosmic Ray Spectrum at Energy $\sim$10$^{17}$ eV by Yakutsk Data

The paper presents cosmic ray spectrum by Small Cherenkov Yakutsk array data for 20 continuous years of observation. The spectrum is obtained from Cherenkov light flux - the energy scattered by charged particles of air showers in the atmosphere. It has been shown by measurements that in the cosmic ray spectrum there is a break in the slope at energy $ \sim $10$ ^{17} $ eV. The reliability of the result is based on spectra of other compact array experiments and simulations to check for systematic uncertainties, which could affect the shape of the spectrum. Another confirmation is change in mass composition of cosmic ray obtained from longitudinal development of air showers in energy region 10$ ^{16} $-10$ ^{18} $ eV.