Some statistical properties of spiral galaxies along the Hubble sequence

A statistical study has been made for the variations along the Hubble seque nce, of such parameters as the degree of tightness of winding of spiral arm Lambda, the pitch angle mu, the flatness of the disk H/D-25 and the thickn ess H along the Hubble sequence for 365 spiral galaxies published in A&Ap S upplement Series. The mean values of these quantities for the various Hubbl e types have been obtained for the first time. The results of the statistic s show clearly 1) that the Hubble classification of spiral galaxies is one which has only a qualitative and statistical significance, and 2) that the dispersion relation in the density wave theory is valid for most spiral gal axies, i.e., the arms of most spiral galaxies satisfy the requirements of b eing tightly wound.