Published online by Cambridge University Press: 14 August 2015
The various hypotheses on the origin of comets are surveyed, with particular reference to the phenomenon of comet-streaming, as revealed by statistical analysis of the directions of the perihelia of cometary orbits. The difficulties of reconciling comet-streaming with any of the hypotheses of cometary origin is pointed out. It is shown that in the case of the interstellar hypothesis these difficulties may be overcome by supposing that the velocities of incoming comets are decreased through the accretion of material from an Oort cloud of solar-system comets. An estimate is made of the total number of interstellar comets in the Galaxy.