xiv Proceedings. ^February 22nd, igo^. 



suitable Arrangement for Determining the Capacities 

 of Condensers by the Successive Discharge Method." 



Dr. G. A. Hemsalech read a paper (communicated by Dr. 

 C. H. Lees) entitled "On the Spectrum of the Glow 

 Discharge at Atmospheric Pressure." 



Special Meeting, February 22 nd, 1904. 



Professor W. Boyd Dawkins, D.Sc, F.R.S., President, 

 in the Chair. 



Mr. F. SoDDY, M.A., the Wilde Lecturer, gave an experi- 

 mental demonstration of the properties of Radium. 



After a brief reference to the manner in which the element 

 was discovered by Mdme. Curie, he explained that it gave off 

 three kinds of rays, of which by far the most important were the 

 a rays, composed, probably, of particles of helium, these were 

 about the size of an atom of hydrogen, and carried a positive 

 charge of electricity. They had very little penetrative power, 

 being stopped by a single sheet of paper, or even by a few inches 

 of air ; they moved with a velocity of about 20,000 miles a second, 

 and were deviated, though very slightly, in a powerful magnetic 

 field. The other two kinds were the /3 rays, identical with the 

 cathode rays discovered long ago by Sir W. Crookes, and the 

 y rays which were analogous to the Rontgen rays, and had 

 ■enormous penetrative power, an inch of solid steel not sufficing 

 to prevent their escape. 



Mr. Soddy also showed the almost instantaneous action of 

 radium in discharging an electrified body, and the slower action 

 of polonium, which gives off only a rays, in bringing about the 

 same result. 



He described the disintegration of radium as taking place 

 in four stages, as though the atom had four explosive centres. 

 The first disruption liberates the a rays, and leaves an emanation, 

 itself not a permanent form of matter, but capable of again 

 disintegrating and leaving a deposit on solid substances, whereby 



