192 RADIUM. 



trometer and surrounded 1)y paraffin, i i i /, inclosed in the metallic 

 envelope E E E E, which is connected to earth. Since the a rays are 

 but feebly penetrating the}' can not escape, but the fi rays traverse 

 the paraffin and carry off negative electricity, so that the trough A A 

 becomes positiveh' charged, 



A sealed glass test tube containing radium salt becomes spontane- 

 ously charged with electricity, as if it were a Leyden jar. If, after a 

 sufficient time, a line is traced by a glass cutter on the wall of the test 

 tube, a spark may pass at the point where the w^all is thinned by the 

 scratch, and at the same time the operator receives a feeble shock in 

 his lingers l)y the passage of the discharge. 



The group of ft rays is made up of a variety of rays differing in 

 their penetrating power. Some ft rays are absorbed by a thickness of 

 one one-hundredth millimeter of aluminum, while others are able to 

 traverse, before complete absorption, a layer of lead several milli- 

 meters in thickness. Another method of distinguishing the varieties 

 of ft rays is by the curvature of their path in a magnetic field. In the 

 experiment represented in fig. 2 the ft raj's deviated b}^ the magnetic 

 field would darken a photographic plate all the wa}' from B to C. 

 The least deviated rays would be distinguished at C and those most 

 deviated at B. Thus there would appear the photograph of a sort of 

 spectrum produced by the influence of the magnetic Held on the ft 

 rays. B}' interposing a thin sheet of metal in the path of the ra3^s, it 

 may be shown that the rays most deviated are suppressed, so that it 

 appears that the most penetrating rays are least deviated.^' 



According to the ballistic theory, it may be assumed that the ft ra3's 

 are composed of electrons projected with different velocities. The most 

 penetrating ra3's have the highest velocity. Kaufmann's researches, 

 interpreted in the light of the theor}' of electrons as given bj^ M. 

 Abraham, lead to very important general conclusions. Certain ver}^ 

 penetrating ft raj'S may consist of electrons impressed with a velocit}^ 

 nine-tenths of that of light. The propertv of mass in electrons, and 

 perhaps in all bodies, may be a consequence of electro-magnetic reac- 

 tions. The energ}^ required to impress higher and higher velocities 

 upon an electricallv charged body approaches infinity when the veloc- 

 ity of the body approaches the velocity of light. 



The y ra^'S, which are not deviable in a magnetic field, and which 

 are analogous to X-rays, foi'm but a small part of the total radiation. 

 Certain / ra3\s are extremely penetrating, and are able to traverse a 

 thickness of several centimeters of lead. 



Becquerel ra3's ma3' be utilized to make radiographs without special 

 apparatus. A small glass test tul)e containing some hundredths of a 

 gram of radium salt replaces the Crookes tube. Both ft and y rays 

 are emplo3^ed, but such radiographs lack sharpness on account of the 



"Becquerel, C. R., Vol. CXXX, pp. 206, 372, 810. 



