10 M and a mass luminosity ratio equal to 127. Although these investigations are subject to rather large errors of both observational and theoretical origin, they nevertheless indicate, in confirmation of the results derived from the velocity dispersions in clusters, that the masses of galaxies are very much larger than could be inferred from their luminosities. Furthermore, one must make sure that one does not deal with optical doubles or with galaxies which are clearly escaping from one another. Also, it will be necessary to obtain accurate distances of the double galaxies studied. The requirements mentioned for trustworthy determinations of the masses of the components of double galaxies are obviously severe and not easily satisfied.
Independent approaches are therefore most desirable.
What features of multiple galaxies reflect phenomena which took place during the creation of stars and galaxies and what other features are due to evolution or to the effects of rather recent encounters is a most fascinating problem. Far too little, however, is known at the present time about these subjects to permit us to make any statements here, lest we wish to run the danger of indulging in idle speculations. We only recommend that, an attack on multiple galaxies with all of the means at our disposal should certainly prove most fruitful to unravel the mysteries surrounding the origin and the evolution of the large scale aggregates of matter in the universe.