DEPARTMENT OF TERRESTRIAL MAGNETISM. 321 



On possible planetary magnetic effects. L. A. Bauer. Physical Rev., ser. 2, vol. 7, 500 

 (April 1916). Lancaster, Pa. (Abstract of paper presented at the New York 

 meeting of the American Physical Society on February 26, 1916.) 



The question of the existence of cosmical effects arising from possible 

 planetary magnetic fields is engaging the attention of various investigators, 

 especially of astronomers. For example, it has been known for 30 years or 

 more that there are certain irregularities in the motions of the Moon too 

 large to be accounted for by any possible outstanding gravitation effects. 

 Similar irregularities are shown by the motions of Mercury, Venus, and the 

 Earth. It therefore becomes a matter of interest to ascertain, if possible, 

 whether these irregularities in the motions of astronomical bodies can be 

 associated, in any way, with magnetic effects. Accordingly, as a first step, 

 a formula has been theoretically established for determining the field strengt.h 

 of possible magnetic fields enveloping the members of our solar system for 

 which certain requisite constants are known. 



Let Me represent the strength of the Earth's magnetic field at its poles, 

 namely, about 0.65 of a c. g. s. unit, and let oje, Ve, de, ge represent, respec- 

 tively, the Earth's angular velocity of rotation, mean radius, mean density, 

 and gravity at the surface. Give similar significance to the quantities 

 Ma, coq, Ta, da, Qa for any rotating astronomical body (a). Then we may have 

 approximately: Ma : Me = (wa rl da) : (co« r'g de) = (coa fa go) : (we re ge). If, 

 for example, the astronomical body (a) is the Sun (S), there is obtained a 

 field strength (Ms), for the Sun's possible period of rotation as a whole, 

 which agrees within about 10 percent of Hale's provisional value (SOMe). 

 For the planets Mars, Jupiter, and Saturn, whose angular velocity of 

 rotation is known, we get: Mm = 0.2 Me', Mj = 68 Me; ilf, = 24Me. It thus 

 appears that, on the hypothesis made, Jupiter, Saturn, and probably also 

 Uranus and Neptune, may be enveloped by stronger magnetic fields than is 

 the Earth. Jupiter's field may even approach in strength that of the Sun. 

 In conclusion, the possible bearing was pointed out on the vexed outstanding 

 question as to the precise cosmic conditions which determine the period 

 and direction of rotation of a member of the solar system. (See pp. 291-292.) 



The work done by the United States Coast and Geodetic Survey in the field of terrestrial 

 magnetism. L. A. Bauer. Pubhshed in "Centennial Celebration of the United 

 States Coast and Geodetic Survey," 1916, Washington. (One of the addresses in 

 connection with the Centennial Exercises of the United States Coast and Geodetic 

 Survey, April 5 and 6, 1916.) 



In 1856 the number of stations at which the magnetic elements had been 

 determined in the United States was about 160, distributed chiefly along 

 the sea-coast. That was the status of the magnetic work of the Coast Survey 

 six decades ago. At the close of 1915 the stations at which the magnetic 

 elements have been completely determined by the survey number, in the 

 United States proper, about 5,()00, and about 500 in the outlying possessions. 

 They are now found to be more regularly distributed over the large regions 

 covered. About 80 per cent of the total number of stations have been occu- 

 pied during the period 1899 to 1915 and at about 10 per cent the observations 

 have been repeated, from time to time, in order to determine the changes 

 ever going on in the Earth's magnetism. In addition, magnetic data at sea 

 have been accumulated, as opportunity afforded, on cruises of Coast Survey 

 vessels; a number of magnetic observatories (5 at present), where the count- 

 less fluctuations of the Earth's magnetism are being continuously recorded, 

 have been operated; invaluable compilations of all available magnetic data 

 in the United States and contiguous countries have been made; the instru- 



