ABSTRACT
The quantization of an arbitrary system of interacting particles (a liquid) is performed by means of introducing the operators of the density and of the velocity of the liquid; the commutation rules between these operators are determined (§ 1). From the results of this quantization the general character of the distribution of the energy levels in the spectrum of a quantum liquid is determined (§ 2). The temperature dependence of the heat capacity of helium II is investigated (§ 3). It is shown that at absolute zero a quantum liquid can possess the property of superfluidity (§ 4). At non-zero temperatures it is found that two motions — a superfluid and a normal — can simultaneously exist in helium II. This can be described by means of the conception of the superfluid and normal parts of the liquid; the λ -point in helium II is connected with the disappearance of the «superfluid» part of the liquid (§ 5). The experiments made to measure the heat conductivity and viscosity of helium II are interpreted; the thermomechanical effects in helium II are considered (§ 6). A system of hydrodynamic equations is advanced describing the macroscopic motion of helium II (§ 7). By means of these equations the propagation of sound is investigated and it is shown that two velocities of sound must exist in helium II (§ 8).
