344 Mr. C. A. Sadler on 



general to be small compared with that of (a), but later ex- 

 periments showed that this was not universally true. In fact, 

 in some cases the correction due to it became of grave 

 importance. Details of these results will be given later. 



Preliminary experiments showed that in no case did the 

 corpuscular radiation penetrate to a greater distance than a 

 few millimetres in air at atmospheric pressure, so that no 

 ionization due to the corpuscular radiation could be detected 

 at a distance of 1 cm. from the radiating surface. 



If the inner sliding tube was so adjusted that the distance 

 between the aluminium window and the radiator R 3 was 1 mm. 

 and the ionization measured, then the inner tube withdrawn 

 a small distance at a time until the surfaces were about two 

 centimetres apart, the ionization being measured at each stage, 

 it was found that the values of the total ionization increased 

 rapidly at first, and finally at a slower and uniform rate. 

 These readings were corrected in each case for the effect due 

 to the change of electrical capacity of the system involved 

 in the various relative positions of the two surfaces. If the 

 distances apart of the plates be taken as abscissse and the 

 total ionization produced in the ionization-chamber as ordi- 

 nates we obtain the curves shown in PI. V. fig. 5, which 

 represent the total ionization curves with iron as tertiary 

 radiator, Fe, Sr, Mo, and Ag acting respectively as sources 

 of secondary homogeneous radiation. The final straight 

 portion of the curve corresponds to the region in which no 

 corpuscular ionization is produced. It is readily seen from 

 the figure that the corpuscular radiation from iron excited by 

 the homogeneous radiation from silver is of a more penetrating 

 type than that excited by strontium. In practice, a constant 

 deflexion of the gold-leaf in the electroscope E 3 was used, and 

 the corresponding deflexion upon the electroscope E 2 observed. 

 The ratio of the readings of E 3 to that of E 2 , corrected for 

 changes of capacity, gave a measure of the relative ioniza- 

 tions. But the difference in the values of the total ionization 

 when the bounding surfaces were 2 cm. and 1 cm. apart 

 respectively, corresponded to the ionization produced in 1 cm. 

 of air by the effects (c), (d), and (<?). If a proportional 

 amount of this ionization be subtracted from each of the 

 series of readings previously obtained, we get a measure in 

 each case of the ionization due to the corpuscular radiation 

 from sources (a) and (b). 



Plotting the ionizations due to the corpuscular radiation 

 as ordinates against the distance apart of the bounding 

 surfaces as abscissae, we obtain the curves shown in PI. V. 



