20 
IOWA ACADEMY OP SCIENCE 
February. Its length exceeded 100,000 miles and width 60,000 miles. It con- 
sisted of a great compact mass of penumbra with large central umbra and nu- 
merous nuclei, changing more or less from day to day and spectroscopically very 
active, brilliant reversals and diagonal distortions of the hydrogen lines were 
frequent. This disturbance reappeared in the latter part of February and March,, 
but gradually subsided. Other groups of spots only slightly inferior were pres- 
ent in March and July. In the latter month another giant spot appeared which 
during its transit was subjected to many changes in which hydrogen played a 
prominent part with the formation of fissures and bridges. 
August witnessed the return of these disturbances. Another splendid group 
of vast dimensions appeared early in October, not as compact as previous ones^ 
but its separate portions embraced a region of 135,000 miles by 100,000 miles. A 
second one nearly as large and somewhat scorpion-shaped followed it about a 
week later and during the last week a third stupendous spot with large elongated 
umbra indicated something of the gigantic but mysterious forces which are at 
work at the climax of a sun-spot maximum period. The balance of the year wit- 
nessed streams of smaller spots across the spot zones. 
1906. 
The principal characteristics of the 1906 record are: 
1. A slight decrease in the mean daily number of groups, spots and faculae. 
2. Marked fluctuations of activity, followed by periods of distinct decline^ 
spots of the first magnitude being present in January, March, July, August and 
December, with minima in February, September and October. 
3. The increase in number of spotless days; at least eight days in October 
were free from spots. 
Reviewing the record for the present solar cycle so far, the observations this . 
year appear to point to the maximum as having been passed during the latter 
months of the year 1905 and the more gradual and steady decline towards the 
minimum has now set in. 
The principal disturbances of the year were observed in July, when the spot 
zones were studded with both large and small spots, some with “bridged’^ 
umbrae and curious whorls of penumbra studded with circling nuclei. 
1907. 
The numerical results of this year were almost precisely the same as the 
preceding year. The year was remarkable for the number of large spots which 
were visible, every month witnessing one or more “greater” sun-spots, the groups 
of February and June were of giant size and nearlv equalled those of the previous 
year. 
In October four large groups were visible and one increased to a train of very 
large spots of tremendous extent, which made a second transit only slightly re- 
duced in size in November. The year closed with decreasing activity. 
In the subjoined tables are given the monthly summaries of the daily observa- 
tions taken from January, 1903, to December, 1907. The columns are self-ex- 
planatory. 
The results as thus tabulated are indicated graphically in Plate I, which ex- 
hibits the monthly fluctuations during the period under review and also the pre- 
ceding twelve year’s record: 
