CORRELATION WITH SUNSPOTS. 83 



H. H. Turner (1913; cf. Sampson, 1914) has worked out an hypothe- 

 sis which is stimulating, even if not yet acceptable. He supposes that 

 the Leonid swarm of meteors, revolving once in about 33 years in a 

 very eccentric orbit, is at the basis of the sunspot recurrence. These 

 meteors were observed in countless swarms, filling the sky for a 

 few nights in November 1799, and again in 1833 and 1866. In 

 1899 they were expected, but failed to appear in large numbers, 

 having probably been swerved to one side through the attraction of 

 some planet. Turner finds that they have passed near Saturn several 

 times in the last 2,000 years. At some of these encounters a quantity 

 of meteors may have been detached and losing their own velocity may 

 have fallen nearly straight toward the sun, grazing its outer surface 

 in their circuit at a velocity of 400 miles per second, then swinging out 

 to aphelion near their place of encounter, and completing their revolu- 

 tion in about 11 years. Successive returns of the main Leonid swarm, 

 approaches of Saturn, and perhaps even the influence of other planets 

 would be sufficient to perturb this meteoric swarm and cause the 

 variations in period observed. On their terrific flight close to the sun 

 many would be caught in the sun's outer atmosphere, thus in some way 

 causing sunspots. 



This hypothesis attempts to explain the period and its irregularities, 

 including the double and triple period. I refer to it at some length 

 because the investigation of trees gives evidence not only of climatic 

 variations in the sunspot period, but of double and triple sunspot 

 periods and possibly of still larger fluctuations. Turner's hypothesis 

 warrants further discussion to explain why the spots appear in sub- 

 tropical latitudes but not at the solar equator. In the planetesimal 

 hypothesis of Chamberlin and Moulton, the rotation of the sun on its 

 axis is attributed to the material falling back upon it after receiving a 

 slight orbital motion from the visiting star. The authors state that 

 the process may still be going on. This view is sustained by arguments 

 based on the zodiacal light and on meteors, both of which seem best 

 explained as planetesimal matter not yet returned to the solar mass. 

 Matter as yet unabsorbed would very likely consist of particles which 

 had been given just enough orbital motion to escape the surface of the 

 sun on their periodic return. The particles for the most part would 

 then have extremely eccentric orbits and pass close to the sun's surface 

 at tremendous velocity. They would be moving largely in the plane 

 of the solar system and consequently would pass close to the sun's 

 equator. If finally caught in the sun's atmosphere, friction would 

 reduce their motion, turning a large part of it into heat and a part into 

 forward movement of the sun's atmosphere. Thus the planetesimal 

 hypothesis explains the equatorial acceleration. A large meteoric 

 group, as suggested by Turner, is therefore consistent with the hypoth- 

 esis. The undefined zone between the accelerated equator and the 



