46 o THE POPULAR SCIENCE MONTHLY 



solar corona are so distributed, especially at the time of minimum sun 

 spot activity, as to indicate strongly that they were arranged around 

 the sun as a magnetized sphere. It is not necessary here to review the 

 many details which pointed to that conclusion. The great objection to 

 that theory at the time in the minds of scientists consisted in the fact 

 that the sun was too hot to be a magnetized sphere. It was pointed 

 out by me that the earth is certainly a magnetized sphere, and that its 

 interior has a very high temperature. Since those days the discovery 

 of the ionization of matter, whereby dynamic forces of one kind or 

 another disintegrate the atoms, of which molecules are composed, into 

 their primal constituents, which are pure charges of electricity, and 

 the demonstration that the free ions, positive or negative, as the case 

 may be, wander about from place to place and produce magnetic field, 

 have made this theory of the sun much more intelligible. The addi- 

 tional discovery of the Zeeman effect of magnetic field in the sun spots 

 greatly strengthens my theory, and in fact it is not easy to see how 

 solar phenomena can now be discussed on any other general basis. 



The solar output shows itself in an irruption of prominences, in a 

 very extended corona, and in an invisible radiation stretching out to 

 almost unlimited distances in space. The polar magnetic field of the 

 sun, of which the corona is an evidence, will expand to great distances 

 from the center, and its strength may perhaps be detected as far as to 

 the distance of the earth. Electromagnetic radiation stretches out over 

 the solar sphere radially in every direction, a small pencil of the same 

 falls upon the earth in its different positions along the orbit from day 

 to day, and sets the circulation up in the earth's atmosphere which has 

 been described. This solar radiation falling upon the earth's atmos- 

 phere is in part absorbed by it, so that the molecules and atoms yield up 

 their ions, which by redistribution produce the observed phenomena of 

 the earth's electric field, and also certain well-known variations in the 

 strength of the earth's magnetic field. The entire subject is full of 

 difficulties, but at the same time it possesses a fascination to the student 

 such as pertains to very few branches of modern science. This same 

 radiation of the sun falling upon the earth produces the temperatures 

 which vary from place to place, from season to season, and from year 

 to year, in a very complex series of changes which, taken as a whole, 

 constitute what is called the earth's climate. There are many indica- 

 tions that this solar radiation, that is to say, the electromagnetic energy 

 which the sun sends forth into space, is not exactly constant. The sun 

 seems to be a variable star, the variation in its heat and light is the 

 natural consequence of the incessant changes of temperature and pres- 

 sure, in the circulation, the electricity and magnetism, which are going 

 on within the solar mass. We have already been able to show from our 

 studies of the barometric pressure, temperature and vapor pressure in 



