INTRA-ATOMIC ENERGY. 265 



and may also be deflected by a niaonet, but in the opposite direction 

 from that taken by the a radiations. They are the ones that produce 

 the photographic effects. They must be very piMietrating." Their 

 velocity, according- to Kaufmann, must be nearly that of light. 



The y radiations are not deflected b}^ a magnetic field and are proba- 

 bly similar to X raj's and, like them, very penetrating. Their 

 velocity, according to Blondlot, must be exactly that of light; that is 

 to say, 300,000 kilometers per second. 



Besides these various kinds of radiations which have, as wc shall 

 see in a future paragraph, none of the properties of jnatter, radio- 

 active bodies emit, in an infinitely small quantit}^, an emanation hav- 

 ing the character of a gas, which can be condensed by means of liquid 

 air at a temperature of —150"^ and is made up, according to Ramsay, of 

 helium. It gives to bodies with which it comes in contact a tempo- 

 rary radio-activity. The product of the condensation, whose proper- 

 ties are shown by the action of the electrometer, is invisible and 

 imponderable, but it can be dissolved in certain acids, and on e\apo- 

 rating the solution the radio-activity is obtained, unchanged, in the 

 residue. 



The effluvia of radio-active bodies have very active physiological 

 properties that have already l)een studied by many observers. Con- 

 centrated radium, even when incased l)y a metallic envelope, l)urns 

 the skin. It paralyzes bacteria. 



Induced radio-activity, discovered by Rutherford, is that phe- 

 nomenon l)y virtue of which radio-active bodies, especially in solution, 

 communicate for some time their radio-activity to surrounding bodies, 

 either insulating or conducting. It seems quite evident that in this 

 case we are dealing with material substances, since induced radio- 

 activity is not effected through glass and mica, and may be carried to 

 a distance from radio-active bodies. On blow^ing the disengaged par- 

 ticles through a coiled tube and projecting them upon any body what- 

 ever, the latter soon acquires a temporary radio-activity. 



It is by induced radio-activity that is produced the phosphorescence 

 of sulphide of zinc inclosed in a glass receiver communicating by a 

 large tube with another receiver containing a solution of radium. Bis- 

 muth plunged for some daj^s in a solution of nitrate of radium finallj'-, 

 for the same reason, becomes phosphorescent. All radio-active bodies 

 are more active in solution than in a solid state, but then they lose their 

 phosphorescence and can only induce it b\" their emanations. 



«In this, as Rutherford says, tliey do not resemble the cathodic rays, since the 

 latter, as Lenard has slinwn, will lianlly traverse metallic layers no thicker than 

 one one-hundredth of a millinictci-. It is probable, rather, that the penetration of 

 metals is due tu the X rays that always accompany these radiations or that are at 

 least always entienderefl 1)v thcni. 



