H. Skey. — On perioiHc vertical Oscillations in the Sun's Atmosphere. 93 



the conclusion that there is no upper limit ; still it may be inferred that the 

 great bulk of the sun's atmosphere is below a certain fixed limit. Now if a 

 range of temperature of say 100° Fall., can account for the movements 

 which at times take place in the earth's atmosphere, how much more readily 

 must it be acknowledged that the commotions which have occurred on the 

 solar globe in the remote past would be fully competent to produce an 

 oscillatory motion in the sun's atmosphere. 



But it may be asked what proof have we of these hypothetical oscilla- 

 tions, for we cannot take a barometer to the solar orb ? It is not, however, 

 improbable that the sun-spots may prove to be a solar barometer, so nicely 

 adjusted, that we may, though at a distance of more than ninety-two 

 millions of miles, study the meteorology of the sun. And it is to be hoped 

 that this subject will not be thought uninteresting, when we consider that 

 our own terrestrial meteorology is not only connected therewith, but abso- 

 lutely dependent thereon. Many solar discoveries have been made during 

 the last few years, but they appear to shroud the sun and its surroundings 

 in still more numerous mysteries ; no wonder, therefore, that various theo- 

 ries have been developed to attempt their explanation. 



Amongst these mysteries may be mentioned : 



1. The periodicity of the solar spots. 



2. Their first appearance in each cycle along two belts more than 20° 

 distant from the equator, and their gradual appearance nearer to the equato- 

 rial regions as the epoch of minimum is approached. 



3. The acceleration of their rotation in proportion to their vicinity to 

 the sun's equator. 



4. Their greater prevalence north of the sun's equator. 



Such are some of the greatest difiiculties which beset every theory 

 relating to the solar spots. As present theories do not I think explain 

 these, I have ventured upon another, which, be it ever so plausible, will 

 still require to be submitted to all possible tests, and if found untenable 

 must be dismissed from our minds without further ceremony. 



In attempting to explain such solar phenomena, we must bear in mind 

 that a rhythmic motion characterizes not only the ponderous planets, but also 

 the most attenuated comets. These bodies are so amenable to the laws of 

 gravity, that their periods from aphelia to perihelia are calculable with 

 wonderful exactness. 



Now the law of gravitation comes into operation, not only when a 

 comet is attracted by a sun into a very elongated orbit — having its peri- 

 helion passage very close to the sun, and its aphelion immensely distant — 

 but it must also act on any other gaseous, or vapourous mass in his 

 neighbourhood, which can be attracted sufficiently near a direct line to the 



