22 
IOWA ACADEMY OF SCIENCE 
Plate 2 represents graphically the yearly curve of the seventeen year’s ob- 
servations, both of the mean number of groups and average number of spots in 
the groups, the former being indicated by the lower smooth line and the latter 
by the upper dotted one. 
Bibliography of author’s published sun-spot observations since 1902: 
The Recent Large Sunspots. Popular Astronomy, Vol. XI, December, 1903. 
Review of Solar Observations, 1902. Ibid. Vol. XI, November, 1903. 
Review of Solar Observations, 1903. Ibid. Vol. XIII, April, 1905. 
Review of Solar Observations, 1904 and 1905. Ibid. Vol. XIV, December, 1906. 
Review of Solar Observations, 1906. Ibid. Vol. XV, December, 1907. 
