June 21, 1918] 



SCIENCE 



621 



The potentials of certain magnetized bodies (il- 

 lustrated by lantern slides) : Louis A. Bauer, 

 Ph.D., D.Sc, director of the department of terres- 

 trial magnetism, Carnegie Institution of Wash- 

 ington. The author has had occasion in connection 

 with various problems to establish, in a convenient 

 form, the mathematical expressions for the poten- 

 tials and field-components of certain magnetized 

 bodies of revolution, such as, for example, ellip- 

 soids of revolution and elliptic homeoids. The ex- 

 pressions usually found in treatises either stop at 

 those for the problem of gravitation, or apply only 

 to special cases, or they are not given in the most 

 elegant or convenient form possible for mapping 

 out readily the magnetic field surrounding the bod- 

 ies. Not infrequently, moreover, the published ex- 

 pressions are found to contain errors of one kind 

 or another. 



Development of magnetic susceptibility in man- 

 ganese steel by prolonged heat treatment: Charles 

 Francis Brush, Ph.D., ScD., LL.D., of Cleveland. 



Accelerometers : N. W. Akimoff, of PhUadel- 

 phia. 



Luminescence of radium salts: D. H. Kabakjian, 

 assistant professor of physics, University of Penn- 

 sylvania, and E. Karrer, of Philadelphia. All 

 radium salts luminesce in the dark at ordinary 

 room temperature. It has been found that when a 

 radium compound is heated to a critical tempera- 

 ture it will almost completely lose its luminosity 

 while at this temperature, but when it is again 

 cooled to room temperature it will acquire a lumi- 

 nosity which is many times (from ten to fifty 

 times for radium bromide, barium bromide) its 

 original luminosity. This property of radium com- 

 pounds has been investigated as regards the fol- 

 lowing points: (1) Eelation between luminosity 

 and the maximum and minimum temperatures to 

 which the salts have been exposed; (2) decay of 

 the acquired luminosity with time; (3) degree of 

 recovery of luminosity after decay by reheating; 

 (4) relation between luminosity and chemical com- 

 position of the salt. The phenomena described in 

 the paper can probably be explained if it be as- 

 sumed that with the greater molecular freedom im- 

 parted to the salt at the higher temperatures cer- 

 tain groupings of molecules are formed which are 

 stable at the higher temperatures but unstable at 

 the ordinary room temperatures. The breaking 

 down of these groups by the action of alpha, beta, 

 gamma rays produces the luminescence. These 

 groupings would correspond to the so-called "ac- 

 tive centers" which are postulated by Eutherford 



in his discussion of luminescence of zinc sulphide, 

 but differ essentially from them by the fact that 

 these can be destroyed and reformed over and 

 over again by heating the compound, whereas the 

 active centers in zinc sulphide, once destroyed, can 

 not be recovered by any simple process. 



Saturday Morning, April gfl; George Ellery Hale, 



Ph.D., Sc.D., LL.D., F.R.8., Vice-president, 



in the Chair 



Motions in the stellar systems Struve 18S6 and 

 Struve SOS: Eric Doolittle, professor of astron- 

 omy. University of Pennsylvania. Any double star 

 in our catalogues may be a system of two suns, 

 which are revolving about one another under the 

 action of their gravitation, or their apparent con- 

 nection may be only an accidental; one star may be 

 immeasurably farther away than the other and 

 they may only appear to be near together because 

 they are in the same direction from us. In the 

 latter case, measures will in time show that the 

 one sun is drifting past the other in a straight 

 line; in the former, the one will move about the 

 other in an elliptic orbit. The two cases examined 

 present especial difficulty because in each case the 

 companion is moving directly toward the principal 

 star in a straight line. Originally the stars were 

 widely separated; now they are close together and 

 are only visible as a double star in the largest 

 telescopes. The path may be an ellipse, in which 

 case we view it almost edgewise, and if this is the 

 case the motion of the companion will be ap- 

 parently reversed as it passes about its orbit and 

 the motion will soon become very rapid. Observa- 

 tions of such systems should be secured now, while 

 the companion is at a critical part of its path. 

 It was found that each of the two systems exam- 

 ined were true physical systems and that the mo- 

 tion was in each case orbital. 



The number of the spiral nebulw: H. D. Curtis, 

 astronomer. Lick Observatory, Mt. Hamilton, Calif. 



Soldiers' and sailors' insurance: Samuel Mc- 

 CuNE Lindsay, Ph.D., LL.D., professor of social 

 legislation, Columbia University, New York. 



Italy in the Triple Alliance: William Roscob 

 Thayer, Litt.D., L.H.D., LL.D., Cambridge, Mass. 



Ballistic experiments by a new (?) method: 

 Arthur Gordon Webster, Sc.D., LL.D., professor 

 of j)hysic3, Clark University, Worcester, and Mil- 

 dred Allen. 



Some considerations on the ballistics of a gun of 

 seventy-five miles' range: Arthur Gordon Web- 

 ster, Sc.D., LL.D., professor of physics, Clark 

 University, Worcester. 



