DEPARTMENT OF TERRESTRIAL MAGNETISM. 309 



intensity exerted by such a shell on points within the hollow interior is zero, 

 and on external points anywhere infinitely near the homoeoid it is perpendicu- 

 lar to the surface, directed inward and equal to 47r pt, where p is the constant 

 density of the homogeneous mass and t is the thickness of the shell at the point 

 for which the force of attraction is sought.^ Since, furthermore, any two 

 confocal homoeoids of equal masses produce the same intensity on all points 

 external to both, we have in general that the total intensity exerted by a homo- 

 geneous elliptic homoeoid on an external point (x, y, z) is equal to I^-k pt, p being 

 the constant density and t the thickness of the elliptic homoeoid at the point {x, 

 y, z), confocal to the given homoeoid and passing through x, y, z; the intensity is 

 along the normal and directed inward, or toward the given shell. 



On the basis of equation (1) and MacLaurin's theorem the author has 

 deduced: (1) expressions for the field of an inductively magnetized rotation 

 elUpsoid in a more convenient form for the general case than previous ones; 

 (2) expressions for the field of an inductively magnetized prolate elHptic 

 homoeoid, established possibly for the first time. 



It was also shown that expressions in finite form may be estabhshed for 

 the field of an inductively magnetized eUiptic homceoid in general — that it 

 is not necessary to assume a rotation elliptic homceoid. This matter is of 

 special interest in view of the fact that expressions for the field of an induc- 

 tively-magnetized solid ellipsoid, in general, have not yet been established 

 in finite form. In conclusion, various applications of the derived formulae were 

 given. 



Meeting of the International Geodetic and Geophysical Union at Brussels, July 18-28, 1919.* 

 Louis A. Bauer. 



Under the auspices of the International Research Council there were 

 established at Brussels, during the meeting of the Council in the Palais des 

 Academies, July 18 to 28, 1919, various international unions of astronomy, 

 mathematics, physics, chemistry, biology, geodesy and geophysics, scientific 

 radio-telegraphy, etc. 



The International Geodetic and Geophysical Union, as finally estabhshed 

 for a period of 12 years beginning on January 1, 1920, consists of the sections 

 and officers shown in the table on the following page. 



Since there were represented at Brussels this time only the Alhed Nations 

 and the United States, it was concluded to defer complete organization of the 

 sections until the entrance into the Union of other counties to be invited by the 

 International Research Council. In the case of Section (6) (Seismology), since 

 the agreement among nations belonging to the International Seismological 

 Association, formed before the war, does not expire until April 1, 1920, it 

 was necessary to postpone any organization, whatsoever, of the section, 

 s* The Executive Committees of the Sections were for the present hmited to the 

 president, vice-president, and secretary, excepting in the case of (e) (Physical 

 Oceanography), where Sir Charles Close (British Ordnance Survey) and Mr. 

 G. W. Littlehales (U. S. Hydrographic Office) were made additional members 

 of the executive committee of that section. 



The'officers of the Union are: President, M. Charles Lallemand (director, 

 Levehng Service, France) ; general secretary, Colonel H. G. Lyons (Army 

 Meteorological Service, Great Britain). These two ofiicers, with the addition 

 of the presidents of the sections, who are the vice-presidents of the Union, 

 constitute the Executive Committee of the Union. 



^ Thomson and Tail's Natural Philosophy, pt. ii, paragraph, 519-525. 



* Abstract of articles "Geophysics at the Brussels Meetings, July 18-28, 1919," Science, 

 October 31, 1919, pp. 399-403, and of Teriestrial Magnetism and Electricity at the Brussels 

 Meetings, July 18-28, 1919, Terr. Mag., vol. 24, pp. 105-112. 



