324 CARNEGIE INSTITUTION OF WASHINGTON. 



can not be explained by gravitation forces may not have to be ascribed to 

 interacting planetary magnetic effects. It is thus seen that the problems of 

 the Earth's magnetism, or of magnetism in general, lead to the very outer 

 boundaries of human knowledge. They may play an important part in the 

 solution of questions of a fundamental nature. (See pp. 321 and 330.) 



Note on rotation periods of planets. L. A. Bauer. (Read before meeting of American 

 Astronomical Society at Swarthmore, August 31, 1916.) 



If magnetic fields result from the fact that the bodies which they envelop 

 rotate about certain axes, the question of the rotation-periods of planets and 

 the direction of rotation, becomes one of interest to the student of cosmical 

 magnetism. Unfortunately, only in the case of half of the planets, namely, 

 the Earth, Mars, Jupiter and Saturn, is the period of rotation and the direc- 

 tion of rotation definitely known. 



In putting together all known facts regarding the planets, it was noticed 

 that for the four named the product of the angular velocity of rotation, co, 

 into the orbital velocity of the planet about the Sun, v, hence cov, was a con- 

 stant quantity within about 14 per cent of its mean value. Thus taking 

 u}V as unity for the Earth, we have for Mars 0.80, for Jupiter 1.05, and for 

 Saturn 0.76; the mean value for the four planets is 0.90. 



On the results of some magnetic observations during the solar ecUpse of August 21, 1914. 

 L. A. Bauer and H. W. Fisk. Terr. Mag., vol. 21, 57-86 (.June 1916). Wash- 

 ington. 



This is a compilation and discussion of observations made by and in coop- 

 eration with the Department of Terrestrial Magnetism respecting a possible 

 magnetic effect during the time of the solar eclipse of August 21, 1914. In 

 accordance with L. A. Bauer's circular letter of June 23, 1914, magnetic and 

 allied observations were made at 23 stations distributed over the Earth, the 

 results of which are tabulated in this paper. 



A preliminarj" review of the magnetic results is next given. Confining 

 chief attention to the stations nearest the belt of totality, the following con- 

 clusion is drawn : 



"There appears to be good reason for believing that an observable mag- 

 netic effect occurred during the time of the solar eclipse of August 21, 1914, 

 at stations within the region of visibility, the effect being larger for stations 

 near the belt of totality than for those farther away." 



A diagram showed the magnetic-declination changes at Eskdalemuir, 

 Stony hurst, Kew, and Rude Skov, August 21, 1914. A bay occurred at each 

 of these stations a few minutes before the time of maximum obscuration. 

 As the result of this bay, the customary progression of the compass needle 

 towards a westerly extreme was interrupted, and a retrograde movement 

 occurred which continued for some time. Of the four stations, the bay was 

 most developed at Rude Skov (Denmark), the nearest one, of the present list 

 of stations, to the belt of totality. The total range of this minor oscillation 

 was at Rude Skov, about 2', or the amplitude was 1', which is the order of 

 magnitude of similar oscillations observed at some previous eclipses.^ 



The Greenwich mean time of the lowest point of the bay occurred later 

 and later in passing fiom Eskdalemuir to Rude Skov, and approximately, 

 according to the same rate that the phase of maximum obscuration progressed 

 from station to station. The occurrence of a magnetic effect at various 

 stations, not at the same absolute time nor at the same local time, but related 

 in some manner to the rate of progress of the shadow cone, may have to be 

 regarded as one of the chief characteristics of a possible eclipse effect.^ This 



»See, L. A. Bauer's articles in Tor. Mag., vol. 5. 14:5-10.5, 1900, and vol. 7, 155-102, 1902. 



