e 

 m 



782 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1908. 



proximately found, sliowing whether the emanation should have a 

 sensible electric deviation. Becquerel made the calculations and pre- 

 pared the experiment at the same time that the Curies demonstrated 

 directly that the deviable rays of radium carried negative charges. 

 On March 26, 1900, at the Academie des Sciences, he published the 

 confirming results. Dorn independently published the same results, 

 depending on the calculations of Becquerel. 



Knowing the radius of curvature for a cathode ray in a known 



magnetic field and its electrostatic deviation, we may calculate 



and 0. AVhen his discovery was well assured Becquerel published 

 figures obtained from the absorption in black paper, giving 



'y=2.37XlO" and -- = 1.32X10% very close to the last given by 



in 



Kauifmann. 



Wliile Becquerel struggled against his insufficient means for con- 

 structing the necessary in vacuo apparatus, Kauffmann completed ex- 



periments with sufficient accuracy to conclude that — varies with the 



velocity — that is to say, that mass, the constant which has seemed so 

 well established since the time of Newton, has no absolute existence 

 and that we can consider its coefficient as constant only with veloci- 

 ties infinitely small compared with the velocity of light. We will say 

 nothing further on this aspect of radio-activity. It now passes out 

 of Becquerel's domain. Indeed before the flood of foreign investiga- 

 tions which furthered his results and before the new results secured 

 every day, he had to leave to others the experiments for which he bad 

 neither the material nor the means. 



After the a and the /3 rays had been clearly distinguished by the 

 experiments already stated, it w^as questioned wdiether the former 

 are only slightly deviable or not deviable at all. Rutherford per- 

 formed an experiment from which lie concluded that they are slightly 

 deviable but his conclusion was too involved to carry conviction. 

 Becquerel took up the question, using accurate measures made upon 

 his photographic plates, and Avas able to establish a weak deviation 

 undoubtedly, the a rays forming a pencil clearly defined and not 

 showing any sensible magnetic dispersion. These rays are analogous 

 to the canal rays of Goldstein. The curvature of the a rays seemed to 

 augment with the length of path in the air. Although the great 

 absorption of the rays by the air made difficult the simultaneous study 

 of the magnetic and electric deviation, the problem was solved by 

 Des Coudres. The experiments of Becquerel and of Rutherford 

 proved that the change of curvature in traversing a thin sheet of 

 aluminum is due to a noticeable retardation of the charged corpuscles. 



