in Conducting Sheets and Solid Bodies. 23 



radiation, we must be prepared to admit that, owing to the 

 enormous convection effects which take place in the sun, 

 combined with the great velocity at its surface due to its 

 rotation in 26 days, convective currents of electricity on an 

 enormous scale are possible in it whose magnetic effect might 

 be felt at the earth. It is easy to verify that, if the sun were 

 equivalent to a magnet with 13,000 times the earth's intensity 

 of magnetization (i. e. if it were magnetized rather more 

 strongly than we can magnetize steel), it could produce a 

 variation of t Jq of the earth's total force. 



Our object is to point out the effect of the conducting 

 atmospheric layer on all such hypotheses. If its conduc- 

 tivity is sufficiently high, it will screen off all such external 

 influences except the components parallel to the earth's axis 

 of rotation; and in any case it will partly screen them off, 

 and at the same time produce a lagging behind the sun of an 

 amount determined above. On the other hand, if, adop ting- 

 Sir C. W. Siemens's hypothesis, we were to suppose that the 

 outer part of this conducting stratum did not participate 

 fully in the rotation of the earth, currents would be induced 

 in it which would screen external space from the part of the 

 earth's magnetism which is not symmetrical round its axis, 

 and the reaction of these currents would tend to keep the 

 atmosphere rotating. 



The sudden and very brilliant outburst of light that was 

 observed on the sun by Carrington in 1859 was shown to be 

 accompanied well within an interval of 15 seconds by a very 

 sudden and well-marked disturbance of the magnetometers, 

 w^hich, however, went on increasing afterwards (vide Balfour 

 Stewart, loc. cit.). Now the light took about eight minutes 

 to reach the observer; and it seems therefore that we have good 

 warrant for concluding that this magnetic disturbance was not 

 propagated from the sun directly and practically instanta- 

 neously, as was shown long ago by Laplace to be the case with 

 gravitation; but that either (1) it was an immediate indirect 

 effect produced in the atmosphere by the sudden increase of 

 radiation, or (2) it was an effect propagated from the sun 

 with the same velocity as light. 



Gahvay, Xov. 13, 1883. 



