170 ANNUAL REPORT SMITHSONIAN INSTITUTION, 193 8 



general alternate peaks are much more sharp in their formation than 

 the intervening ones. The long drawn-out maximum of 1927-29 

 should, therefore, be followed by a relatively sharp peak. With the 

 rapid rise upward during the last year and the high maximum of last 

 July, my own view is that the present maximum cannot carry beyond 

 1938 without a substantial trend downward in the average sunspot 

 numbers. 



Mr. Clayton's analysis of the sunspot cycle from 1750-1910 has 

 led him to attempt a prediction from 1910 to 1955, using only the 

 data accumulated previous to his predicted curve. The rather 

 remarkable correspondence between his predicted curve and the 

 observed curve from 1910 to date suggests that his independent fore- 

 cast for a maximum at the end of 1937 or the beginning of 1938 lends 

 an increased interest to the critical part of the curve in which we 

 find ourselves at present. 



There is another important variation in the characteristic of sun- 

 spots of which we must not lose sight. This is the apparent drift in 

 the positions of the spots toward the solar equator as the cycle 

 progresses. At the beginning of the sunspot cycle the spots first 

 appear in the neighborhood of 35° either side of the sun's equator. 

 This was exemplified in the case of the present sunspot cycle which 

 started in 1934 with high latitude spots. As the solar cycle advances, 

 the spots increase in number and tend to break out at progressively 

 lower latitudes on the sun. While there is some fluctuation back and 

 forth in latitude from day to day and month to month, the trend is 

 always toward the equator. As the sunspot period approaches the 

 maximum, the average latitude for the maximum number of spots is in 

 the vicinity of 15° both for the northern and the southern hemispheres. 

 After the maximum the spots decrease in size and number but they 

 continue to break out at decreasing latitudes. The end of the cycle 

 is marked by infrequent spots occurring when they are seen on either 

 side of the sun's equator in latitudes ranging from 2° to 5°. By the 

 time this state is reached the next cycle has begun again with spots 

 breaking out once more in high latitudes. 



This peculiar trend of latitude during the sunspot period is so far 

 without any adequate explanation. Observation of latitudes, how- 

 ever, helps very much in diagnosing where we may be with respect 

 to the sunspot cycle at the present time. The average latitude of the 

 spots of both hemispheres during the last 3 months has been 15.5° 

 and leads us to believe, therefore, that we are now very close to the 

 present sunspot maximum. By the end of 1938 it would appear that 

 we will find solar activity definitely on the down grade, in which case 

 the next sunspot minimum should arrive not far from 1944. 



If we knew what was the cause of sunspots, it would help very much 

 in solving the mystery of the solar cycle aud in predicting the future 



