Long-range Particles from Thorium C. 573 



the deflexion of particles of range 8*6 cm. was ^hus 1*08 times 

 that for the particles of 11*3 cm. range. 



If the particles of range 11*3 cm. are ordinary a particles, 

 the relative deflexion of a. particles of range S'6 and 11'3 cm. 



to be expected is a / __^ = 1'10, since the velocity of the 



ct particles varies as the cube root of the range. The observed 

 values by the two methods are 1'10 and 1'08, or a mean 

 of 1"09. By making a number of experiments, no doubt the 

 relative bending could be determined with more precision; 

 but this was not thought necessary, as the agreement is suffi- 

 ciently close to indicate that the long-range particles from 

 thorium C are ordinary a pai tides of mass 4. It is of interest 

 to note that if these long-range particles were atoms of 

 mass 3 carrying two charges such as are observed to be 

 released as a consequence of the collision of a particles with 

 N and C atoms, the deflexion of the a particles of 8'G cm. 

 range should be '90 of that of the particles of 11'3 cm. range 

 instead of the observed value of 1*09. The data on which 

 this calculation is based have been given in the Bakerian 

 Lecture (loc. cit.). 



The experiments recorded in this paper thus negative the 

 idea that particles of mass 3 are ejected from thorium C. It 

 should be pointed out that the agreement of the atomic 

 weights of radium, uranium-lead, and thorium-lead with the 

 values calculated from the emission of « particles show that 

 no particles of mass 3 are expelled in the main series of 

 radioactive changes of uranium and thorium. Similarly, no 

 certain evidence has been obtained of the emission of H atoms. 

 From numerous experiments I have made, I am inclined to 

 believe that most of the H atoms observed from a source of 

 radium C under normal experimental conditions must be 

 ascribed to occluded hydrogen. 



It has been generally considered that the expulsion of two 

 distinct sets of a rays from thorium C is a proof that this 

 product suffers a dual transformation. From analogy with 

 the dual disintegration of radium C, it is supposed that 

 35 per cent, of the atoms of thorium break up with the 

 emission of a particles of range 5'0 cm., giving rise to 

 thorium D, which breaks up with the expulsion of a /3 particle. 

 The reverse process is considered to take place in the other 

 branch, 65 per cent, of the atoms of thorium C first emitting 

 /3 particles and giving rise to thorium C. which is very 

 rapidly transformed with the emission of the swift a particles 



