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VI. 



EADIANT MATTER.' 



By JOHN JOLY, Sc.D., F.R.S., 

 Professor of Geology and Mineralogy in the University of Dublin. 



(Plate III a.) 



. [Ordered for Publication May 9. Published June 9, 1911.] 



Radiant matter is, in many respects, the most important manifestation 

 associated with radioactivity which modern researcli has brought to light. 

 This claim is justified by facts which it is my purpose in this lecture to deal 

 with briefly and in outline. 



We shall commence our studies by observing and detecting for ourselves 

 the existence of radiant matter. I have projected upon the screen the image 

 of a gold-leaf electroscope. There is a curved celluloid scale just beyond 

 the range of the leaf, but in the same plane, so that its divisions and the 

 image of the leaf are alike clearly defined upon the screen. There is in the 

 base of the electroscope a small opening. It is now closed by a slip of glass 

 about one millimetre thick. We notice first that the leaf is practically 

 stationary. It retains its charge so perfectly that even with the help of the 

 scale we cannot see any movement. I now place just beneath the slip of 

 glass covering the aperture a speck of a salt of radium. Observing the 

 leaf carefully, we perceive a slow movement indicating a gradual discharge. 



The loss observed under these conditions is due to rays of two kinds 

 which are given out by the radioactive substances present : rays known as 

 j3 and J rays. They pass with facility through the glass, and confer upon 

 the air in the electroscope the properties of a conductor of electricity. We 

 cannot here fully discuss the nature of these rays. It is sufBcient to recall 

 that they are very penetrating — more especially the y rays ; that the latter 

 are probably of the nature of the X rays, and represent the transmission 

 of a pulse or shock in the ether; and that the former are of the nature of the 

 cathode rays which have been shown by Sir J. J. Thomson to consist of 

 negatively electrified particles moving at a very great velocity, and possessing 

 a mass about the thousandth part of that of an atom of hydrogen. These 

 particles are very certainly subordinate parts of the atom, and are expelled 



1 A Lecture delivered before tlie Eoyal Dublin Society on February 3rd, 1911. 



SCIENT. PROC. K.D.S., VOL. XUI., NO. VI. N 



