DEPARTMENT OF TERRESTRIAL MAGNETISM. 323 



Then, again, the amount of magnetic activity is not necessarily commensu- 

 rate with that of solar activity, whatever measure of the latter be used. When 

 the comparisons between the solar data and magnetic data are made for 

 intervals of less than a year, a month for example, as was done in the author's 

 1909 paper^, the lack of exact synchronism and the lack of proportionality 

 between the two sets of changes become especially noticeable. 



Fortunately, beginning with 1905, we have a new set of figures, the values 

 of the solar constant, determined with high precision at Mount Wilson, Cali- 

 fornia, by Dr. Abbot. Remarkable fluctuations are shown in these values, 

 amounting at times to 10 per cent of the value. The present paper made a 

 comparison between the annual changes in the values of the solar constant 

 for the period 1905 to 1914 with the irregularities in the annual changes of 

 the Earth's magnetic constant. It is found that the two sets of data, in 

 general, show similar fluctuations. Also, a closer correspondence is found 

 between these two sets of changes than between either set and that of sun- 

 spot frequencies. In brief, the solar-constant values furnish another index 

 of changes in solar activity which may be usefully studied in connection with 

 minor fluctuations in the Earth's magnetism. 



In conclusion, it was pointed out why none of the mentioned criteria of 

 solar activity can be used as an adequate measure of the various ionizing 

 agencies ultimately responsible, according to present belief, for the magnetic 

 changes recorded on the Earth. 



Our Earth a great magnet. L. A. Bauer. Joiu-n. Frank. Inst., vol. 181, 601-628 (May 1916) 

 Philadelphia. 



This was the annual lecture of the Carnegie Institution of Washington for 

 1915, being given before the Trustees and their guests at Washington on 

 December 9, 1915. Although three centuries have elapsed since Gilbert in 

 his famous treatise on the magnet, published in 1600, declared "the terrestrial 

 globe itself is a great magnet," the only improvement which we might make 

 would be to say: If the Earth is not a magnet, it certainly acts like one. 



Since every magnet is surrounded by the so-called magnetic lines of force, 

 then, since the Earth acts at least like a magnet, it also must be similarly 

 enveloped. It is the object of magnetic surveys to map out these lines of 

 force of the Earth. The Earth's magnetic poles are, on the average, 1,200 

 miles and more distant from the Earth's true or geographic poles, and they 

 are not even on opposite sides of the Earth. If a straight line were drawn 

 through the Earth's magnetic poles, it would not pass through the Earth's 

 center, but be 750 miles away from it. Owing to the complexity of the 

 Earth's magnetization, the compass does not point exactly north and south, 

 except at very few places. Furthermore, the compass is continually changing 

 its direction, by amounts which make it necessary to issue new magnetic 

 charts for the use of mariners at intervals preferably not over 5 years. There 

 is thus made apparent not only the need of magnetic surveys, but, likewise, 

 the repetition, from time to time. 



The extensive magnetic-survey work conducted by the Carnegie Institu- 

 tion of Washington, through its Department of Terrestrial Magnetism, on 

 land and at sea, was next described, and the various operations were illus- 

 trated by showing lantern-slides and motion pictures taken on the Carnegie's 

 cruise in 1915 from Brooklyn to Panama. 



The belief is becoming current that every rotating member of the solar 

 system is surrounded by a magnetic field, and astronomers are much interested 

 at present in ascertaining whether outstanding astronomical motions which 



iSee Terr. Mag., vol. 19, 116-119, 1914. 



