384 UNSUSPECTED RADIATIONS. 



organic bodies (printing ink, varnishes) will act on a photographic 

 plate b}' their "emanations." exactly as if the plate had been acted 

 upon l»y light, the ])c)ile(l oil of the printing ink and the turpentine in 

 varnish being the active substances. Remarkably clear photographs 

 of a printed page and a lithographic print were thus o])tained without 

 the aid of liglit. iSIany organic su])stances act in the same wa^', and a 

 piece of old div ])f)ard gives its likeness simply after having been hiid 

 for some time over a photographic lilm, while a plate of polish(>d zinc, 

 separated from the him l)y a sheet of paper, will send its radiations 

 through the paper and give a photographic reproduction of its water- 

 marks.' 



In what relation these "emanations'* stand to the Becqucrel rayw 

 can not yet be deteniiined. But it becomes more and more certain 

 that, like the kathode rays, the Becciuercd radiations also consist of 

 material particles projected from the radio-active bodies and carrying 

 electricity with them. They may possibl}^ be accompanied b}?^ vibra- 

 tions of ethei" of the nature of light, but the fact of a real transport 

 of particles of matter is rendered more and more apparent by the 

 researches of Bec<iuerel, the Curies, Elster and Geitel,^ and Ruther- 

 ford.^ The " emanations"' from thorium comjiounds are even affected 

 by drafts in the room. But these emanations are neither dust nor 

 vapors. They must be atoms, or ions, of the radiating bod}^ and 

 they comnumicate radio-activity, and, consequently, the power of dis- 

 charging electricity to the surfaces of the bodies with which they (;ome 

 in contact. From glass that " acquired " activity may be washed away, 

 while to other bodies it clings like a sprinkling of the "jack-frost" 

 powder, and ]M. Curie is described in Nature as being unable for a time 

 to make electrostatic experiments on account of this "acquired" radio- 

 activity.* Moreover, the Becquerel radiations exercise a chemical 

 action; they ozonify air, as they " ionize" it, and a glass bottle which 

 contains salts of radium takes a violet color, thus showing that chem- 

 ical processes are provoked by the radiations.^ 



' Proceedings of the Royal Society, Vol. LXI, p. 424. Bakerian lecture, delivered 

 on the 24th of March, 1898; Nature, the 28th of April, Vol. LVII, p. 607. 



^Verhandlungen der deutschen physischen Gesellschaft, 1900, p. 5; summed up in 

 Naturwisi^enschaftliche Rundschau, Vol. XV, p. 10.3. 



=* Philosophical Magazine, 1899, Vol. XLVII, p. 109; 1900, Vol. XLIX, pp. 1, 161. 



*See E. Rutherford's paper in Philosophical Magazine, 1900, Vol. XLIX, p. 161; 

 also Nature. 



^ A salt of uranium may be submitted to absolutely any chemical transformations, 

 but when you return to the salt from which you started in your work, you find in it 

 the very same electrical radio-activity which it had at the start. Impurities do not 

 affect it. The radiation seems thus to belong to the molecule of uranium, and hardly 

 to be influenced by external causes. (Sklodowska-Curie, in Revue Gen^rale, 1899, 

 X, p. 47.) 



