DEPARTMENT OF TERRESTRIAL MAGNETISM. 309 



phenomenon, such as prominences. The central position of the sun- 

 spots of May 14 to 15 last, the character of their formation, and the 

 time of the year, were favorable to the production of a magnetic dis- 

 turbance on the Earth. In these studies various measures of solar 

 activity are being tried out (see pp. 348-351). 



Besides the relationships referred to in the first paragraph, it has 

 been found that there is another geophysical phenomenon — atmos- 

 pheric electricity — between which and solar activity a definite re- 

 lationship exists, as described on page 350. The electric potential 

 gradient of the air, on days free from disturbing influences, and also 

 the range of its daily fluctuation, are found to increase, in general, 

 with increased solar activity. 



It further results from our preliminary studies that the Earth and 

 probably the other planets are apparently sending out into space or 

 returning, by a sort of reflex action, a portion of the electrified par- 

 ticles continually received from the Sun; as a result the Earth exerts, 

 apparently, upon sun-spot activity, a small but observable electric 

 effect of a double-wave character during the year. On the average, 

 the maximum Earth-effects occur at the times of the year, near the 

 equinoctial months, when magnetic disturbances and polar lights are 

 most frequent, and the minimum Earth-effects occur near the sol- 

 stitial months, when magnetic disturbances and polar lights are least 

 frequent (see p. 351). It would appear more and more that besides 

 those of gravitation, there are other bonds of union — electrical in 

 their nature — between the Earth, the sister planets, and our parent 

 Sun, by means of which the cosmic forces responsible for electric and 

 magnetic effects, such as we observe, are conveyed. 



OCEAN WORK. 



The Carnegie's present world cruise (No. VI) of total length 64,044 

 nautical miles, begun at Washington on October 9, 1919, was com- 

 pleted at the same port on November 10, 1921. The success attend- 

 ant upon this cruise, referred to in the report of 1920, has continued 

 throughout the current year. The commander, J. P. Ault, and his able 

 staff, deserve much credit for the successful management of the vessel 

 and for their persistence under difficulties as well as for the quaUty 

 and quantity of the observational data obtained. The prompt trans- 

 mittal of the observed data to the office at Washington has made it 

 possible to continue supplying promptly to the leading hydrographic 

 establishments the data required for correction of the magnetic charts 

 used by mariners. The steady improvement in these charts since 1905, 

 when our ocean magnetic work was begun, is very gratifying (see 

 table 1, p. 342). 



The present cruise up to the arrival of the Carnegie at Washington, 

 November 10, 1921, is shown delineated on the accompanying map. 



