1906.] 0)1 Astronomical Consequences of Pressure of Light. 841 



orbit, but in an elliptic orbit it acts as if it were a force resisting 

 change of distance, and therefore it tends to make an elliptic orbit 

 even more circular. 



Applying these considerations to a comet regarded as a swarm of 

 small particles coming into our system, a sorting action will at once 

 begin. The smaller particles will have their period of revolution 

 lengthened out more than the larger ones, and they will tend to trail 

 behind. The Doppler emission effect will damp down the motion, 

 and again, more markedly with the smaller particles, and all will tend 

 to spiral into the sun. The Doppler reception effect will tend to 

 destroy the ellipticity of the orbit, more especially with the smaller 

 particles, and ultimately the particles of different sizes may move in 

 orbits so different that they may not appear to belong to the same 

 system. In course of time they should all end in the sun. Perhaps 

 the zodiacal light is due to the dust of long dead comets. 



It appears just possible that Saturn's rings may be cometary 

 matter which the planet has captured, and on which these actions 

 have been at play for so long that the orbits have become circular. 



[J. H. P.] 



