December 18, 1903.] 



SCIENCE. 



771 



intricacies of the radiations of these radio- 

 active bodies, without doubt the last named 

 has given us the clearest conception of their 

 nature. Professor Rutherford, as a result 

 of his investigations, resolved them into 

 three classes, which for convenience are 

 designated a. fi.ajid y rays. They possess 

 the following characteristics: 



I. "The a-rays are very slightly pene- 

 trating, and appear to constitute the prin- 

 cipal part of the radiation. These rays 

 are characterized by the laws by which 

 they are absorbed by matter. The mag- 

 netic field acts very slightly upon them, 

 and they were formerly thought to be quite 

 unaffected by the action of this field. How- 

 ever, in a strong magnetic field, the a-rays 

 are slightly deflected; the deflection is 

 caused in the same manner as with cathode 

 rays, but the direction of the deflection is 

 reversed; it is the same as for the canal 

 rays of the Crookes tubes. 



II. "The (J-rays are less absorbable as a 

 whole than the preceding ones. They ai-e 

 deflected by a magnetic field in the same 

 manner and direction as cathode rays. 



III. "The ;--rays are penetrating rays, 

 unaffected by the magnetic field, and com- 

 parable to Roentgen rays." 



From the experiments given above it ap- 

 pears that the ?--rays alone suffice to in- 

 tensify the fluorescent properties of the 

 bluish-white tiffanyite diamond. 



While it is quite beyond the scope of this 

 paper either to contribute much that is 

 novel as to the real nature of radium or 

 even to speculate thereon, some refei'ence to 

 a few of the numerous recent researches is 

 essential for a clear understanding of a 

 part of that which follows. 



Professors Rutherford, Soddy and Dewar, 

 and Sirs "William Ramsay, AVilliam Crookes 

 and William Iluggins, with Lady Hug- 

 gins, have obtained helium from radium 

 preparations which are luminous in the 

 dark. Professors Soddy and Ramsay have 



obtained helium from thorium oxide, which 

 is also radio-active, as first observed inde- 

 pendently by G. C. Schmidt and Madame 

 Curie. Indications are that the luminosity 

 of radium has some relation with this 

 stellar and telluric element and it has been 

 intimated that its propulsion constitutes 

 the a-rays. Professor C. Vernon Boys 

 has even suggested that the tails of comets 

 may be accounted for, perhaps, by the 

 evolving of this form of radio-activity. W. 

 E. Wilson and Joly have made the 'sugges- 

 tion that the presence of radium in the sun 

 might enter as an important factor in con- 

 tributing to solar radiations.' 



Radium preparations are to be had on 

 the market from French and German 

 sources which are iton-linninous. We are 

 not informed as to efforts to secure helium 

 from this variety. AVe do know, however, 

 that certain minerals, as willemite and 

 kunzite, become strongly fluorescent and 

 phosphorescent under the influence of 

 luminous radium compounds. Further, as 

 the result of experiment of one of us, we 

 know that pulverized willemite Immediately 

 glows in the dark when in contact with non- 

 luminous radium barium carbonate of 100 

 activity, as do also certain diamonds, and 

 the minerals mentioned above. 



Thorium dioxide does not become lumin- 

 ous in contact with the radi^im prepara- 

 tions we have been able to obtain, although 

 Elster and Geitel state that a thorium 

 oxide screen shows scintillating fluorescence 

 even after positive electrification, similar 

 to the zinc blende. 



Why certain rays either alone or through 

 their influence upon the surrounding media 

 present the order of magnitude of visible 

 light waves, we shall not undertake to say. 

 It is quite evident, however, that particular 

 substances, like the diamond, willemite, 

 kunzite, etc., possess the power of 'stepping 

 up or down,' as it were, the ethereal stresses 

 propagated by the radium, so that visible 



