308 CARNEGIE INSTITUTION OF WASHINGTON. 



before totality followed by an equally rapid and pronounced decrease for 

 about 10 minutes after totality. Neither of these movements, however, is in 

 marked contrast to the course followed by this element throughout the after- 

 noon. 



(e) The ionic content of positive sign n+ appears to have passed through 

 a maximum simultaneously with X+, but lack of observations during the 

 middle part of the eclipse prevents a positive statement on this point. 



(/) The ionization in a closed vessel, due to the penetrating radiation, 

 apparently was unaffected by the passage of the ecUpse. 



(g) Observations throughout 24 consecutive hours showed a large diurnal 

 variation for all the elements under observation except the ionization in a 

 closed vessel. They also showed for all elements a strong similarity between 

 night conditions and those prevailing on June 8 during and shortly after 

 totality. 



The field of a uniformly magnetized elliptic homaoid and applications. Louis A. Bauer. 

 Jour. Wash. Acad. Sci., vol. 9, 267-269. (Paper presented before the Philo- 

 sophical Society of Washington, February 15, 1919.) 



There have been repeated occasions in the course of the author's investiga- 

 tions when he had need for the simplest possible expressions defining the 

 magnetic field of certain magnetized bodies, such as ellipsoids of revolution, 

 homceoids, focaloids, and cylinders. A variety of investigations will be found 

 in treatises and papers by eminent authors, but the derived expressions either 

 stop at the gravitation potential and intensity components, or but special 

 cases of magnetization are treated. Furthermore, the published expressions 

 for general cases are often needlessly complex, or they contain errors of one 

 kind or another which in some instances have been repeated by later authors. 

 Hence, the attempt was made to derive the desired expressions in the simplest 

 manner possible for practical application. 



According to Poisson, who first solved the problem of induced magnetism 

 in an ellipsoid placed in a uniform magnetic field, if V be the gravitation 



dV 



potential at the point (x, y, z) of a body of uniform density p, then — -— is 



ax 



the magnetic potential of the same body uniformly magnetized in the direction 



X with the intensity A= p. Similarly with regard to any other direction of 



uniform magnetization. If the uniform magnetization results from magnetic 



induction, the magnetizing force at all points in the interior of the body wiU 



be uniform and parallel; so that if the external magnetizing force is uniform 



and parallel, the magnetic force resulting from the magnetization will also be 



uniform and parallel for all points in the interior of the body. 



The ellipsoid is the only body for which -r— is a Hnear function of the coor- 



ox 



dinates x, y, z in the interior, and V, accordingly, a quadratic function of the 



coordinates. Poisson's method can, therefore, be apphed to the case of the 



ellipsoid. 



Hence ii A, B, and C be the intensities of magnetization parallel to the three 



axes of the ellipsoid, and X', Y', and Z' the gravitation components of a 



homogeneous ellipsoid of uniform density p = 1, the magnetic potential of the 



ellipsoid at any external point as resulting from the induced magnetization 



will be: 



V=-AX'-BY'-CZ' 



As defined by Thomson and Tait,' "an elliptic homoeoid is an infinitely 

 thin shell bounded by two concentric similar elHpsoidal surfaces." The total 



* Thomson and Tait's Natural Philosophy, pt. ii, p. 43, footnote 2. 



