On Prof. Arrhenius' Theory of Cometary Tails and Auroræ

Abstract

THE object of my letter to which Prof. Cox refers was to draw attention to certain statements made in recent accounts of Arrhenius' theory which were disproved by Prof. Schwarzschild's computations. I was fully aware at the time that Arrhenius himself had already arrived at the conclusion that, to accord with his theory, the particles in the tails must be assumed to be liquid or solid. This was the necessary result of his computations, which had convinced him that the diameters of the particles must be between 0.1 and 6 in order to satisfy Prof. Bredichin's values for the repulsive forces observed in comets. But how does Arrhenius' theory account for the presence of luminous vapours in the tail? In some recent comets the typical spectrum of the hydrocarbons was traced by Prof. Vogel to the farthest end of their tails. The emission of Comet 1881 iv. (Schæberle) was almost entirely gaseous, and in Comet 1882 ii. even the sodium vapour was observed in the brighter parts of its luminous appendage. How are these vapours carried into the extreme parts of the tail, since the analysis of Prof. Schwarzschild shows that the pressure of light is far too insignificant to exert a repulsion upon the molecules of a gas or vapour?