Physics. 319 



accumulated towards the basic end. By treating a solution of 

 very active uranium nitrate with ammonium carbonate in excess, 

 a small flocculent precipitate was obtained which showed great 

 radio-activity ; it was found, however, that the active body was 

 not wholly insoluble in ammonium carbonate. The precipitate 

 just mentioned gave in five minutes as strong an action upon the 

 sensitive plate as is given in 24 hours by ordinary ui'anium 

 nitrate. The author calls the active substance provisionally 

 "UrX." Thus far he has not observed any special spectrum for 

 the substance. He decides that UrX is certainly distinct from 

 " polonium," because the rays emanating from it penetrate glass 

 while polonium rays do not. It is not so easy to settle whether 

 UrX is distinct from radium, although many arguments point to 

 its not being radium. 



Experiments have been commenced by the author, which tend 

 to show that thorium may be separated into an active and inactive 

 body. 



It is the author's opinion that in the present state of our 

 knowledge of radio-active bodies it is safest to retain an open, or 

 even a slightly sceptical mind. He calls attention to the fact 

 that we recognize them mainly by photographic and electrical 

 tests — reactions which give strong results even when the active 

 body is present in too small a quantity to be detected by the 

 spectrum — one of the most delicate of tests. He remarks that 

 the radiographic test is cumulative. If no action is apparent at 

 the end of an hour, one may be shown after twenty-four hours. 

 If a day's exposure will show nothing, try a week's. The article 

 concludes with the following sentence : " Considering my most 

 active UrX does not contain sufficient of the real material to 

 show in the spectrograph, yet is powerful enough to give a good 

 impression on a photographic plate in five minutes, what must be 

 its dilution in compounds which require an hour, a day, or a week 

 to give an action?" — Chem. JVeios, lxxxi, 253, 265. h. l. w. 



2. Electrical conductivity of Gases traversed by Cathode 

 Rays. — Starting from the results reached by J. J. Thomson and 

 Rutherford in regard to the conductivity of gases traversed by 

 Rontgen or uranium rays, owing to the production of positive 

 and negative ions within them, J. C. McLennan shows that 

 cathode rays impress a similar condition upon a gas. The con- 

 ductivity produced by the cathode rays is explained as due to 

 the motion of the ions, positive and negative, produced in the 

 gas by the radiation. The ionization by cathode rays was found 

 to be about 300 times that due to intense Rontgen radiation. 

 On experimenting with different gases, the result was established 

 that to determine the relative ionization produced in two gases 

 by cathode rays of the same intensity it is sufficient to deter- 

 mine the. absorbing power of the two gases for the same rays. 

 It is also probably true that the ionizations produced by rays of 

 constant intensity traversing different gases at the same pressure 

 are proportional to the densities of the gases. The calculated 



