THE SOLAR SURFACE DURING THE PAST FIVE YEARS— A REVIEW OF 
SUN-SPOT OBSERVATIONS MADE AT ALTA, IOWA, FROM 1903 TO 1907. 
BY DAVID E. HADDEN. 
The present paper is a continuation of a series of sun-spot observations con- 
tributed to the Iowa Academy of Sciences at the annual session in December, 
1902.* 
For the purpose of representing graphically the resulting curve of the sun- 
spot cycle which now embraces two maxima and one minimum the numerical 
summaries of the seventeen year’s observations have been plotted. The instru- 
ments used were a 4-inch refractor until August, 1907, and after that time a 
5l^-inch refractor, an 8-inch reflector was also employed and a polarizing eye- 
piece magnifying about 80 was principally used. 
The means of obtaining the heliographic positions of the spots and faculae 
and the hours of observations were the same as given in my former paper. 
The detailed daily account of the observations have been sent regularly as here- 
tofore to the Solar Section of the British Astronomical Association and the yearly 
results published in Popular Astronomy. 
During the period now under review 810 groups were observed on the sun’s 
disk on 1007 days of observation, distributed as follows: 
Years 
Groups 
Observations 
1903 
93 
230 
1904 
155 
172 
1905 
192 
202 
1906 
189 
198 
1907 
181 
205 
Reviewing the sun-spot cycle of the past 17 years the minimum of 1889.6 was 
followed by a maximum about 1893.7, an interval of 4.1 years, the next minimum 
occurred in 1901.5, or 7.8 years later and the apex of the last maximum was 
probably passed in 1905.9, a difference of 4.4 years. 
*Proc. la. Academy Science, Vol. X. 
2 
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