REVIEW OF ASTEONOMY^ — PUISEUX. 133 



more favorable to stability and are just such as correspond to the 

 distances and velocities of the retrograde satellites. 



An analogous conclusion is drawn by Eddington from the statistics 

 of the elements of the comets. The positions of their aphelia, as a 

 rule, group about two directions which seem to depend in no way 

 upon the general movement of the solar system. These directions 

 rather reveal the direction of the elongation of the one or two primi- 

 tive rings at the expense of wliich the comets were formed. The 

 short-period comets form an exception possibly because they are 

 endowed with a shorter longevity. They are to be considered as 

 revolving in their actual orbits through the intervention of the 

 greater planets. Thus the comet Neujmin (1913c), discovered 

 the Cth of September, 1913, was the third member of the cometary 

 family of Saturn. It was remarkable for its almost constant stellar 

 aspect. The Westphal comet (1852, IV), refound September 26, 

 1913, by Delavan, underwent in October a considerable and unex- 

 plained decrease in brightness. 



In comparison with the ]danets and the stars the comets are doubt- 

 less ephemeral. What becomes of the matter — tenuous, to be sure, 

 but in time abundant — which is left in their wake? Fessenkoff con- 

 siders that it must expand in the region of the ecliptic in the form of 

 a vast flattened, lens-shaped mass centered about the sun and de- 

 creasing in density with increasing distance from the sun. All the 

 well-known traits of the zodiacal light could thus be explained. 

 Fessenkoff believes that certain unsj^mmetrical and changeable fea- 

 tures which have been noted are due to insufficient allowance for the 

 effects of atmospheric absorption. The total mass of the zodiacal 

 matter is certainly very small compared with that of the principal 

 planets, indeed compared with that of the comets and meteors. 



We may suppose that certain meteors are efficacious for troubling 

 the surface of the sun because they are subject to closer approaches 

 to it. Turner was led to adopt the idea, formerly held by J. Herschel, 

 while trying to represent the variable frequency of sun spots by a 

 series of periodical terms. For a course of years certain constant 

 values may be adopted for the coefficients of these terms, and then 

 these values have to be altered. The epochs of all these perturba- 

 tions, according to Turner, fall close to the time of the perihelion 

 passage of the Leonides. It is true the distance of the Leonides 

 from the sun, even at perihelion passage, is somewhat great and 

 necessitates recourse to a secondary stream derived through the inter- 

 vention of some planet. This theory finds a certain degree of con- 

 firmation in the Chinese Annals, which record ancient increases in 

 the number of sun spots at epochs when the Leonides swarm must 

 have passed close to Saturn. 



