392 .Scientific Intelligence. 



merely to the quantity of matter through which a beam of 

 Rontgen radiation of definite intensity passes, being independent 

 of the kind of matter. 



These results, and the agreement between the energy experi- 

 mentally determined and that calculated, led to the conclusion 

 that this radiation is due to what may be called a scattering of 

 primary X-rays by the corpuscles or electrons constituting the 

 molecules of the substance. 



On the hypothesis that Rontgen rays consist of a succession of 

 electro-magnetic pulses in the ether, each electron in the medium 

 through which these pulses pass has its motion accelerated by 

 the intense electric tields in these pulses, and consequently is the 

 origin of a secondary radiation, which is most intense in the 

 direction perpendicular to that of acceleration of the electron, 

 and vanishes in the direction of that acceleration. The direc- 

 tion of electric intensity at a point in a secondary pulse is per- 

 pendicular to the line joining this point and the origin of the 

 pulse, and is in the plane passing through the direction of accel- 

 eration of the electron. 



On this theory, a secondary beam whose direction of propaga- 

 tion is perpendicular to that of the primary, will be plane polar- 

 ized, the direction of electric intensity being parallel to the pulse- 

 front in the primary beam. If the primary beam be plane 

 polarized, the secondary radiation from the charged corpuscles or 

 electrons has a maximum intensity in a direction perpendicular to 

 that of electric displacement in the primary beam, and zero 

 intensity in the direction of electric displacement. 



The secondary radiation from light substances was too feeble 

 to allow accurate measurement of the intensity of the tertiary 

 radiation. 



A consideration of the method of production of primary Ront- 

 gen rays in an X-ray tube, however, leads one to expect partial 

 polarization of the primary beam proceeding from the anti- 

 cathode in a direction perpendicular to that of propagation of the 

 impinging cathode rays, for there is probably at the anti-cathode 

 a greater acceleration along the line of propagation of the cathode 

 rays than in a direction at right angles ; consequently in a beam 

 of X-rays proceeding in a direction perpendicular to that of the 

 cathode stream there should be greater electric intensity parallel 

 to the stream than in a direction at right angles. 



Such a beam was therefore used as the primary radiation, and 

 the intensity of secondary radiation proceeding in a direction 

 perpendicular to that of propagation of the primary beam from a 

 radiator placed in that beam, was studied by means of electro- 

 scopes. 



In the final form of apparatus the intensity of secondary radia- 

 tion was measured in two directions perpendicular to that of 

 propagation of the primary radiation and to each other, while 

 the intensity of the primary beam was measured by a third elec- 

 troscope. 



