336 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1908. 



produced in a suu spot surrounded by a vortex iu which the direction of revolu- 

 tion is cloclxwise. As a negative charge revolving clockwise produces a field 

 of the same polarity as an electric current flowing counter-clocliwise, we may 

 conclude that the magnetic field in spots is caused by the motion of negative 

 corpuscles. 



PROBABLE SOURCE OF THE NEGATIVE CORPUSCLES. 



We may now consider the probable source of a sufiicient number of negative 

 corpuscles to produce a field of about 2,900 gausses in sun spots. 



In his Conduction of Electricity through Gases (p. 164) J. J. Thomson writes 

 as follows : 



" "We thus are led to the conclusion that from an incandescent metal or glow- 

 ing piece of carbon ' corpuscles ' are projected, and though we have as yet no 

 exact measurements for carbon, the rate of emission must, by comparison with 

 the known much smaller rate for i)latinum, amount in the case of a carbon fila- 

 ment at its highest i»oint of incandescence to a current equal to several amperes 

 per square centimeter of surface. This fact may have an important application 

 to some cosmical phenomena, since, according to the generally received opinion, 

 the photosphere of the sun contains large quantities of glowing carbon ; this 

 carbon will emit corpuscles unless the sun by the loss of its corpuscles at an 

 earlier stage has acquired such a large charge of positive electricity that the 

 attraction of this is sufficient to prevent the negatively electrified particles from 

 getting right away from the sun ; yet even in this case, if the temperature were 

 from any cause to rise above its average value, corpuscles would stream away 

 from the sun into the surrounding space." 



On another page (168) Thomson also remarks: " The emission of the negative 

 corpuscles from heated substances is not, I think, confined to the solid state, but 

 is a property of the atom in whatever state of physical aggregation it may occur, 

 including the gaseous." After illustrating this in the case of sodium vapor, 

 Thomson adds (p. 168) : 



" The emission of the negatively electrified corpuscles from sodium atoms is 

 conspicuous, as it occurs at an exceptionally low temperature. That this emis- 

 sion occurs iu other cases, although at very much higher temperatures, is, I think, 

 shown by the conductivity of very hot gases (or at any rate by that part of it 

 which is not due to ionization occurring at the surface of glowing metals), and 

 especially by the very high velocity possessed by the negative ions in the case 

 of these gases. The emission of negatively electrified corpuscles from atoms at 

 a very high temperature is thus a property of a very large number of elements, 

 possibly of all." 



Thus the chromosphere, as well as the photosphere, may be regarded as 

 copious sources of negatively electrified corpuscles. The part played by those 

 corpuscles iu sun spots can not be advantageously discussed until the nature of 

 the vortices is better understood." At present it is enough to recognize that the 

 supply of negative electricity appears amply sufiicient to account for the magnetic 

 fields. * * * 



EXTERNAL FIELD OF SUN SPOTS, 



We have already seen that the strength of the field in sjiofs aiii)ar('ntly changes 

 very rapidly along a solar radius, and is small at the upper level of the chromo- 

 sphere. 



°' For this reason a discussion of the very intei'esting suggestion of Prof. E. F. 

 Nichols, that the positively and negatively charged particles are separated by 

 centrifugal action in the spot vortex, is reserved for a subsequent paper. 



