152 ANNUAL REPOET SMITHSONIAN INSTITUTION, 1913. 



izing apparatus is so adjusted as to transmit one component of a 

 line doubled by a magnetic field, this disappears and is replaced by 

 the other component when the direction of the current is reversed. 

 In other words, one component is visible alone when the observer 

 looks toward the north pole of the magnet, while the other appears 

 alone when he looks toward the south pole. If electrons of the same 

 kind are rotating in opposite directions in two sun-spot vortexes, the 

 observer should be looking toward a north pole in one spot and to- 

 ward a south pole in the other. Hence the opposite components of 

 a magnetic double line should appear in two such spots. As our 

 photographs show, the result of the test was in harmony with my 

 finticipation. 



I may not pause to describe the later developments of this investi- 

 gation, though two or three points must be mentioned. The intensity 

 of the magnetic field in sun spots is sometimes as high as 4,500 

 gausses, or 9,000 times the intensity of the earth's field. In 

 passing upward from the sun's surface the magnetic intensity de- 

 creases very rapidly — so rapidly, in fact as to suggest the existence 

 of an opposing field. It is probable that the vortex which produces 

 the observed field is not the one that appears on our photograph, but 

 lies at a lower level. In fact, the vortex structure shown on spectro- 

 heliograph plates may represent the effect rather than the cause of 

 the sun-spot field. We may have, as Brester and Deslandres suggest, 

 a condition analogous to that illustrated in the aurora: Electrons, 

 falling in the solar atmosphere, move along the lines of force of the 

 magnetic field into spots. In this way we may perhaps account for 

 the structure surrounding pairs of spot§, of opposite polarity, which 

 constitute the typical sun-spot group. The resemblance of the struc- 

 ture near these tw^o bipolar groups to the lines of force about a bar 

 magnet is very striking, especially when the disturbed condition of 

 the solar atmosphere, which tends to mask the effect, is borne in 

 mind. It is not unlikely that the bipolar group is due to a single 

 vortex, of the horseshoe type, such as we may see in water after 

 every sweep of an oar. 



We thus have abundant evidence of the existence on the sun of 

 local magnetic fields of great intensity — fields so extensive that the 

 earth is small in comparison with many of them. But how may we 

 account for the copious supply of electrons needed to generate the 

 powerful currents required in such enormous electromagnets? Neu- 

 tral molecules, postulated in theories of the earth's field, will not 

 suffice. A marked preponderance of electrons of one sign is clearly 

 indicated. 



An interesting experiment, due to Harker, will help us here. 

 Imagine a pair of carbon rods insulated within a furnace heated to 

 a temperature of two or three thousand degrees. The outer ends of 



