IOWA ACADEMY OF SCIENCES. 77 



1892. 



The year 1892, like that of 1891, was one of great increase 

 and activity in all solar disturbances. It would be almost 

 impossible to give a detailed account of the many groups 

 of interest which appeared during the year in a paper of 

 this kind, without the use of drawings or photographs to 

 illustrate the appearance of the intricate markings in the 

 large groups. Among the numerous outbursts, however, 

 those of February 5 18th, May 28d-olst, June lS-28th, July 

 3d-15th, July 24th to August 7th, August 13-25th, Septem- 

 ber 7-lSth, and October 29th to November 6th, were 

 especially fine. The great spot of February was probably 

 the largest visible on the sun's disc in many decades, and 

 was the largest ever photographed on the sun; its length 

 exceeded 100,000 miles and the area 2,000,000,000 square 

 miles. 



Several beautiful groups were present in June, accom- 

 panied by great activity and numerous spots, exceeding 

 100 on some days. July and August were rich in magnifi- 

 cent groups, some containing enormous umbr-cC in large 

 and complicated penumbra? of various forms; these 

 remarkable disturbances were accompanied by some 

 incomparably brilliant manifestations of terrestrial elec- 

 tricity in the form of Aurora Borealis. The solar surface 

 during these months was dotted with eight to thirteen 

 large groups of spots daily. 



1893. 



All solar phenomena continued to increase during this 

 year; the average daily number of grou})s and spots com- 

 bined, reached a maximum during the month of August, 

 after which a marked decline set in, with, however, several 

 fluctuations for a couple of years later. August then 

 marked the apex of the sun-spot cycle extending from 1889.6 

 to 1901.5, the length of the period from minimum to maxi- 

 mum being about 4.1 years, and from maximum to mini- 

 mum, 7.8 years. 



