The present paper is a continuation of a series of sun-spot observations contributed to the Iowa Academy of Sciences at the annual session in December, 1902. For the purpose of representing graphically the resulting curve of the sunspot cycle which now embraces two maxima and one minimum the numerical summaries of the seventeen year's observations have been plotted. The instruments used were a 4-inch refractor until August, 1907, and after that time a 5½ inch refractor, an 8-inch reflector was also employed and a polarizing eyepiece magnifying about 80 was principally used.
Proceedings of the Iowa Academy of Science
©1908 Iowa Academy of Science, Inc.
Hadden, David E.
"The Solar Surface During the Past Five Years - A Review of Sunspot Observations Made at Alta, Iowa, from 1903 to 1907,"
Proceedings of the Iowa Academy of Science, 15(1), 17-24.
Available at: https://scholarworks.uni.edu/pias/vol15/iss1/7