36 PLEASANT WA YS IN SCIENCE. 



storms are also more numerous at the time of maximum 

 spot-frequency, and auroras are then more common. (The 

 reader will not fall into the mistake of supposing that 

 magnetic storms have the remotest resemblance to hum- 

 vanes, or rainstorms, or hailstorms, or even to thunderstorms, 

 though the thunderstorm is an electrical phenomenon. 

 tVhat is meant by a magnetic storm is simply such a con- 

 dition of the earth's frame that the magnetic currents tra- 

 versing it are unusually strong.) 



Thus far, however, we have merely considered relations 

 which we might fairly expect to find affected by the sun's 

 condition as to spots. A slight change in his total brightness 

 and in the total amount of heat emitted by him may 

 naturally be looked for under circumstances which visibly 

 affect the emission of light, and presumably affect the 

 emission of heat also, from portions of his surface. Nor 

 can we wonder if terrestrial magnetism, which is directly 

 dependent on the sun's emission of heat, should be affected 

 by the existence of spots upon his surface. 



It is otherwise with the effects which have recently been 

 associated with the sun's condition. It may or may not 

 prove actually to be the case that wind and rain vary in 

 quantity as the sun-spots vary in number (at least when we 

 take in both cases the average for a year, or for two or three 

 years), but it cannot be said that any such relation was ante- 

 cedently to be expected. When we consider what the sun 

 actually does for our earth, it seems unlikely that special 

 effects such as these should depend on relatively minute 

 peculiarities of the sun's surface. There is our earth, with 

 her oceans and continents, turning around swiftly on her 

 axis, and exposed to his rays as a whole. Or, inverting the 

 way of viewing matters, there is the sun riding high in the 

 heavens of any region of the earth, pouring down his rays 

 upon that region. We can understand how in the one case 

 that rotating orb of the earth may receive rather more or 

 rather less heat from the sun when he is spotted than when 

 he is not, or how in the other way of viewing matters, that 



