DEPARTMENT OF TERRESTRIAL MAGNETISM. 351 



Some new results were set forth concerning an apparent "Earth effect" 

 upon solar activity as discussed by various investigators on the basis of effects 

 observed regarding the asymmetric distribution of sun-spots, faculse, promi- 

 nences, etc., over the Sun's disk. It is found that the effect varies during a 

 sun-spot cycle, as also from cycle to cycle, as shown by the following con- 

 clusions: 



a. A discussion of the sun-spot numbers for the period of 44 years, 1877-1920, indicates 

 the existence of an apparent annual periodicity in sun-spottedness, consisting mainly of a 

 single wave, the minimum occurring about the time (January) when the Earth is nearest 

 to the Sun, and the maximum occurring on the average in July, when the Earth is farthest 

 from the Sun; the average difference between minimum and maximum is found to be about 

 6 sun-spot numbers for the period 1877-1920. 



b. The mean monthly sun-spot numbers for two 70-year periods, 1851-1920 and 1781- 

 1850, show an apparent annual periodicity opposite in phase; for the first period it is of the 

 character described in (a), whereas for the second period it is of the reverse character; 

 accordingly, for the 140-year period, 1781-1920, the apparent annual periodicity is almost 

 eUminated. The periods here mentioned also occur in terrestrial magnetism. 



In deriving conclusions a and b all sun-spot numbers throughout a sun-spot 

 cycle were utilized for the entire period of available data. It is apparent, 

 however, from a combined consideration of a and b, that the annual period- 

 icity in a contains other effects than simply those resulting from the revolu- 

 tion of the Earth around the Sun. The synodic period of Jupiter is 13.11 

 months, and that of Saturn 12.4 months — hence periods differing not greatly 

 from a year. In fact. Dr. T. Royds, of the Kodaikanal Observatory, India, 

 found that prominences were apparently subject to a period of ISVs months.^ 

 Assuming that the disturbing or superposed effects upon the annual period 

 would be a minimum at times of sun-spot minima, the annual variation of 

 sun-spot activity, or the "Earth effect," was deduced only from the three 

 circum-minimum years, i. e., year before, year of sun-spot minimum, and 

 year after. For the entire period of available sun-spot data (1749-1920), 

 15 such circum-minimum monthly means of sun-spot numbers could be formed 

 for each month. The following was found: 



c. Throughout the period of 172 years the annual variation of sun-spot activity near the 

 years of minima is practically of the same character, and consists mainlj' of a double wave. 

 On the average, the maximum "Earth effects" occur at the times of the year, near the equi- 

 noctial months, when magnetic disturbances and polar lights are most frequent, and the 

 minimum "Earth effects" occur near the solstitial months, when magnetic distiubances 

 and polar lights are least frequent ; the average difference between minimum and maximum 

 effect is 3.4 sun-spot numbers for the circum-minimum years of sun-spot activity. 



It would appear from these preHminary studies that the Earth, and proba- 

 bly the other planets as well, is sending out into space or returning, bj^ a sort 

 of reflex action, a portion of the electrified particles continually coming from 

 the Sun ; as a result, the Earth exerts a small but observable effect on sun-spot 

 activity, the action being apparently electrical in its nature. 



The scientific opportunities of the MacMillan Baffin Land Expedition.- Louis A. Bauer. 



With the achievement of the North and South Geographic Poles by intrepid 

 explorers, attention is now fortunately being drawn to the need of a scientific 

 exploration of the polar regions. 



The MacMillan Baffin Land Expedition has a rare opportunity for obtain- 

 ing data and information which unquestionably will materially assist in the 



iKodaikanal Observatory Bulletin No. XXXIIl. 



^Abstract of remarks made at the farewell dinner tendered the MacMillan Expedition by 

 the Rotary Club of Portland, Maine, June 29, 1921. 



