728 Transactions of the American Institute. 



aiice of the earth's magnetism by changes in the sun's atmosphere, he 

 says: Whether the line aurora borealis which succeeded in the even- 

 ing was really the earth's response to this magnificent outburst of the 

 sun is perhaps uncertain ; but the coincidence is at least suggestive, 

 and may easily become something more if the Greenwich magnetic 

 record indicates a disturbance precisely simultaneous with the solar 

 explosion. 



II. Magnetic Perturbations. 



The so-called solar explosion recently described by Prof. Young, of 

 Dartmouth College, did not (contrary to his expectations) produce a 

 specially marked simultaneous disturbance of the magnets in Green- 

 wich observatory. Professor Airy, of the observatory, in answer to 

 Professor Young's inquiry on the subject, writes : " The day was one 

 of magnetic disturbance, but it does not appear that any remarkable 

 movement coincided with the beginning of your observation. There 

 was a sudden movement nearly at the end." It seems probable, 

 therefore, that these rapid and extraordinary movements of the most 

 rarefied portion of the sun's atmosphere do not produce such magnetic 

 disturbances at the earth as have been frequently observed when solar 

 spots appear, which indicate that an actual opening has been made com- 

 pletely through the solar atmosphere. 



Dr. P. H. Yan der Weyde — In the spectroscope, the corona of the 

 sun, the aurora borealis and the zodiacal light produce the same lines. 

 There is a relation between the aurora borealis and also between solar 

 disturbances and magnetic disturbances. That the aurora borealis 

 affects the compass needle is well known. I have at my house a 

 delicate compass needle, carrying a mirror reflecting a scale at some 

 distance from it, so that the slightest motion of the needle is visible. 

 On one occasion I saw, in the afternoon, that the needle was very 

 uneasy, and concluded that there was an aurora, invisible in conse- 

 quence of the daylight. As soon as it was sufficiently dark the aurora 

 became visible. 



Mr. T. D. Stetson inquired if it had been demonstrated, by any 

 sufficient series of observations, that there is any relation between 

 spots on the sun and magnetic or other disturbances on the earth. 



Dr. Yan der Weyde remarked that there had been solar eruptions 

 observed, and at the same instant in two places a change had been 

 observed in the magnetic needle. 



The President — -If the earth is a magnet, it is easy to con- 

 ceive that any change in the form of the sun might affect the 



