H. Skey. — On periodic vertical Oscillations in the Sun's Atmosphere. 95 



lenticular-shaped nebulous mass would in its central portions (or that which 

 is in the same plane as the sun's motion) be dense compared with its other 

 portions, not only from the pull which the planets generally exert, but also 

 from its own gravity. Such central portions have a tendency to disturb the 

 more equatorial regions of the sun's photosphere, especially if a downward 

 oscillation of the lenticular mass is ever exerted. 



That this lenticular mass is not however equidistant all round the sun, 

 but exliibits an elongation in certain directions, has already been attempted 

 to be shown.''' 



The barometric pressure of the earth's atmosphere is greatest in latitudes 

 20° to 35° both sides of its equator, and certainly the greater prevalence of 

 sun-spots about the limiting parallels of 35° on both sides of the sun's 

 equator is a cmious coincidence. Moreover, storms or hurricanes do not 

 occur often at the earth's equator, but 10° or 20° distant therefrom ; this 

 may possibly arise from the fact that no great difference of speed of the 

 atmosphere in miles per hour can occur from the earth's rotation until we 

 reach 10° or 20° of latitude ; the earth's rotation appears to be an import- 

 ant element in their formation. In the earth's case, however, its equatorial 

 parts receive an excess of heat, and from an external source, while in the 

 case of the sun we do not know that a diversity of temperature exists in its 

 different zones. 



We can scarcely suppose, therefore, that heat or any other of the forces 

 of nature could be exerted periodically so as to effect the thinnmg of the 

 photosphere, except that of gravity exerted on an elastic medium. 



"We have thus dealt with the first of the theoretical difficulties of the 

 solar spots, namely their periodicity ; in the second difficulty, or their first 

 appearing in each cycle along two belts more than 20° distant fi'om his 

 equator, we must take into consideration that a gradually increasing 

 pressure, arising from a downward oscillation of a lenticular mass of matter 

 near the plane of the sun's equator would not first affect those parts of the 

 sun quite on the equator (although the greatest pressure might be there) 

 but those parts a few degrees distant therefrom where the photospheric 

 stratum could be pushed away as well as squeezed. 



The first breaks in the continuity of the photosphere from solar storms 

 would therefore show themselves in north and south latitudes, but later in 

 the cycle the more equatorial parts of the photosphere would get pushed 

 away towards both sides until it became in its turn more compressed and 

 pushed away ; spots would therefore gradually be formed nearer and nearer 

 to the equator until those parts in the higher latitudes where they first 

 appeared would be gaining in their thickness of photospheric matter, not 



* " Trans. N.Z. Inst.," Vol. VII., Ait. 15. 



