In the region of galactic longitudes 60 - 74 degree, latitudes +-15 degree and distances from centres of Galaxy 11 - 12 kpc 81 HI clouds are found and their parameters (figure 1) are measured. It has appeared, that the clouds make the "wide" component of gas and are distributed on masses proportionally to M^-3/2.They make 80% of gas on masses, with volume filling factor of 0.23. Average concentration of gas within clouds is 0.15^-3 cm.
The life time of the clouds with such concentration between spiral arms permits to evaluate the velocity of ionization and to choose model of heating interstellar matter satisfying to these data. Besides the presence of the cloud structure between spiral arms is the direct observatinal confirmation of wave theory of formation spiral arms.

Figure 1. The distribution of the HI clouds corresponding to their brightness temperature, Z - coordinate, size, concentration of gas and mass.