476 Messrs. Runge and Precht on the Position 



a spin about the vertical, but also a rolling motion round its 

 axis, (ii.) That even when so spun it is very improbable 

 that its axis would rise to the vertical. 



. It is found, however, that eggs with their axes horizontal 

 generally do rise to the vertical without any delicate adjust- 

 ment of their initial spins. We are therefore forced to 

 conclude that this rising is in some way connected with the 

 phenomenon of limiting friction. To test this, an egg was 

 cast in rough cement and spun on a rough stone. It was 

 found that while the smooth wooden eggs rose with great 

 ease, this cement egg only rose with difficulty,- and usually 

 remained oscillating between two cones as required by the 

 theory for a "perfectly rough" egg. I hope to deal later 

 with the Problem of Columbus, supposing the egg to be only 

 imperfectly rough ; but the analysis promises to be of a much 

 more complex kind. 



I have to thank Professor K. Pearson, who first suggested 

 the problem to me, for a great deal of kind assistance and 

 advice during the course of the investigation. I must also 

 thank Mr. W. Arnold Ogden, Demonstrator in the Department 

 of Applied Mathematics, University College, for the trouble 

 and care he took in plotting the curves for the numerical 

 example and in graphically integrating them. 



XL VI. The Position of Radium in the Periodic System 

 according to its Spectrum. By C. Runge and J. Pkecht*. 



THE spark-spectrum of radium may be splendidly observed 

 by using the bromide recently prepared by Herr Giesel. 

 A few milligrammes, which Herr Giesel was good enough 

 to place at our disposal for this purpose, enabled us, when 

 using a small amount of dispersion, to produce a decidedly 

 more perfect spectrum than any hitherto observed ; and with 

 greater dispersion, to investigate the lines which are capable 

 of being easily photographed, with respect to their behaviour 

 in a magnetic field. As a result we found that the strongest 

 lines of radium are exactly analogous to the strongest lines 

 of barium and the corresponding lines of the related elements 

 Mg, Ca, Sr. As shown by Runge and Paschenf, these lines 

 may be grouped into three pairs, called by them, on account 



* Translated from the Physikcdische Zeitschrift, 4 Jahrgang, no. 10, 

 pp. 285-287. 



t Runge and Paschen, Ber. d. Berl. Akademie, June 26, 1902. 



