WORK OF HENRI BECQUEKEL- — BROCA. 771 



HENRI BECQUEREL BEFORE RADIO-ACTIVITY. 



The problems which preoccupied Becquerel during his entire life 

 related to the constitution of matter and the manner in which this 

 reacts u^Don the magnetic and optical properties of bodies. He 

 approached the problem through rotary magnetic polarization and 

 his theories led him to laws of primordial importance. He was 

 the first to admit that in molecular phenomena there must be a par- 

 tial carrying along of the ether by matter, and from this hypothesis 

 he deduced the formula — 



R 



. .= constant, 



w2 (n^-l) 



where R is the rotation of the plane of polarization and n the index 

 of refraction. Experiment showed this true for bodies, group by 

 group, and while not wholly verifying the theory yet it indicated that 

 he was on the right path and pointed the way for further progress. 



The next step was the study of rotary magnetic dispersion. Verdet 

 had shown that the rotation is nearly proportional to the square of 

 the wave length and that the product of the rotation by the square 

 of the wave length slowly increases from the less to the more re- 

 frangible radiations. Becquerel divided these results by the factor 

 n^ {n-—l), and the result became very nearly constant, indicating 

 how closely his theory as to the connection of ether and matter was 

 connected with these phenomena. 



Verdet noted that in magnetic media the rotation of the plane of 

 polarization is inverse to that in diamagnetic bodies, and that con- 

 sequently there is a difference between magnetism and diamagnetism. 

 For Edmond Becquerel it did not seem so; he believed, rather, that 

 diamagnetic bodies were less magnetic than the vacuum; magnetic 

 ones more so. Henri Becquerel tried to show that the phenomena sup- 

 ported his father's views. He verified the observations of Verdet, 

 but he showed further that magnetic and diamagnetic solutions 

 behave very differently. In the latter case, the action of the diamag- 

 netic molecules is so weak that the rotation is proportional to the 

 concentration. With the former, however, the magnetic action is so 

 strong that the reaction of the molecules upon each other is notice- 

 able. For instance, with the perchloride of iron the rotation in- 

 creases faster than the concentration when the latter becomes great 

 enough. Becquerel verified again the experiment that with mixtures 

 of iron filings and an inert powder the magnetic field increases more 

 rapidly than the number of iron filings. 



Becquerel now asked whether a gas should not have a measurable 

 magnetic rotary power. A\\ the earlier attempts to show this had 

 been unsuccessful. Before making the apparatus adapted to show it 



