82 IOWA ACADEMY OF SCIENCES. 



feather-like prominence was on the west limb; its height 

 was full}^ 90,000 miles. 



1897. 



Like the preceding year, the one now being reviewed was 

 remarkable for several highly interesting groups, especially 

 those of January, May, August, September and December, 

 which appearing about midway between the maximum 

 and minimum of the sun-spot curve, furnished new mate- 

 rial for speculation as to the nature of sun-spot phenom- 

 na. The gradual decline in the total number of groups and 

 spots continued during the present year, with a decided 

 increase in the number of spotless days. The year began 

 with a magnificent group on the disc, from January 3d to 

 15th, which reached a length of about 120,000 miles, and a 

 breadth of about 47,000 miles, and enclosing a area of 

 nearly 2,800,000,000 square miles; this enormous group was 

 in a very active state during its entire appearance, and its 

 umbra was noted as having various tints of color from 7th 

 to 11th, being reddish-brown, shading into gray and green, 

 and finally a uniform black. A considerable group was 

 present early in May, and another one during the closing 

 days of the same month. 



No spots were visible during several days of May and 

 June — forerunners of the minimum yet three years away. 

 During August a fine spot, the largest since January, made 

 the entire transit across the disc. On September 2d a 

 group of small spots appeared at the east limb by solar 

 rotation, in south latitute 12° -15° which, by the following 

 day, became very active with spots increasing, and the 

 hydrogen lines in their spectra reversed and distorted in 

 numerous portions of the group, activity continued every 

 day thereafter until its disappearance, with constantly 

 changing umbra and outlines; strong cyclonic motion was 

 apparent in the penumbra and projecting umbral filaments 

 on the Gth, the motion being counter-clockwise; during 

 the following day the group was breaking up, with shat- 

 tered umbra, crossed by "bridges." The year closed with 



