A MEMOIR OF KLIAS LOOMIS. 747 



visible at each place of observation. These uunibers, when written 

 upon a chart of tiie Northern Hemisphere, showed tliat auroras were 

 by no means equally distributed over the earth's surface. It was found 

 that the region in which they occurred most frequently was a belt or 

 zone of moderate breadth and of oval form, inclosing the North Pole of 

 the earth, and also the North Magnetic Pole. It was therefore much 

 farther south in the Western Hemisphere than in the Eastern. Along 

 the central line of this belt there are more than eighty auroras annually, 

 but on going either north or south from the central line of that belt 

 the number diminishes. 



In 1870, Professor Loomis published a paper of importance relating to 

 terrestrial magnetism, in which he showed its connection and that of 

 the aurora with spots on the sun. That the spots on the sun had peri- 

 ods of maximum and minimum development had long been known. 

 Lamont had noticed a periodicity in the magnetic diurnal variations. 

 Sabine and Wolf and Gautliier had noticed that the two periodicities 

 were allied. The connection of the period of solar spots with conjunc- 

 tion and opposition of certain planets had been shown by De La Kue 

 and Stewart. Professor Loomis undertook an exhaustive examination 

 of the facts that tended to confirm or refute the propositions that had 

 been advanced. He confirmed and added to the conclusions of Messrs. 

 De La Kue and Stewart. He also brought together such facts as were 

 relevant to the question, and he showed that the regular diurnal vari- 

 ation of the magnetic needle was entirely independent of the solar 

 spots, but that those disturbances that were excessive in amount were 

 almost exactly proportional to the spotted surface of the sun. He also 

 showed that great disturbances of the earth's magnetism are accom- 

 })anied by unusual disturbances on the sun's surface on the very day of 

 the storm. 



Various forms of periodicity in the aurora have frequently been sug- 

 gested. Professor Loomis, from all available accounts of the aurora, 

 was able to show that while in the center of the zone of greatest auro- 

 ral frequency auroras might be visible nearly every night, and hence 

 that i)eriodicity could not easdy be shown by means of numbers of 

 auroras recorded in such places, yet that such periodicity was distinctlj' 

 traceable at places where the average number seen was about twenty 

 or twenty-five a year. The times of maxima and minima of the solar 

 si)Ots were seen to correspond in a remarkable manner with the max- 

 ima and minima in the frequency of auroral displays in these middle 

 latitudes. Also from the daily observations made by Messrs. Herrick 

 and Bradley at New Haven during 17 years, he concluded that auroral 

 displays in the middle latitudes of America are generally accompanied 

 by an unusual disturbance of the sun's surface on the very day of the 

 aurora. The magnetism of the earth, the aurora borealis, and the 

 spots on the sun, have thus all three a casual connection, and appar- 

 ently that connection is closely related to the conjunctions and opposi- 

 tions of certain planets. 



