346 Mr. C. G. Barkla on Energy of 

TABLE I. 
Ratio of 
Duration | Deflexion of | Deflexion of | Secondary 
_ Conditions of Exp. | “Gy ny Primary Secondary | Deflexion to 
| | s | Electroscope. | Electroscope.| Primary 
Defiexion. 




Without absorbing) minutes. 
Paes alin ha boca | 24 31°05 10°6 34:1 to 100 
| 2 sheets of ‘Ol cm. 
Al before each 
ee 
) 



electroscope ...... 28 31 10°45 33°7 to 100 
Without absorbing 
DIAS Pte meee 26 30°4 10°5 34°5 to 100 


Without absorbing 
Plabes ier. scadcrate 21 3475 10°3 29°6 to 100 
Sheet of -04 cm. Al 
before each elec- 


TROBCO PO wa cccdeapees 50 30°4 8:15 26'8 to 100 
Without absorbing 
plates’! sre y%1 Goats 30 34°6 9:7 28 to 100 
ee | ee 
Without absorbing 
plates. ih. cacasnsses 29 29:05 113 38°9 to 100 
Sheet of ‘04 em. Al 
before each elec- 

BEOSCOPE 6c. ont. 40 19°5 75 38:4 to 100 
Without absorbing 
WLC. Vda ee ne 30 23°75 9°5 40 to 100 


Without absorbing, 
VOU ESTE Scone bpeaene: 25 26°7 116 43°4 to 100 
Sheet of ‘04 em. Al; 
before each elec- 
| 
i | 
| 
| 

i 
46 20:1 8:45. >| 424 to am 





LEOSCOPE sc, «ance | 
Without absorbing | 
)DIERUS Sah ts IonpLE ANGE | 20 21-2 | 9:2 | 43:4 to 100 

In order to test this equality in penetrative power for rays 
differing enormously in character from those previously dealt 
with, experiments were made with secondary radiation from 
metals to get a secondary beam of sufficient intensity to use 
as a primary in experiments similar to those described. The 
radiation from copper was found to be sufficiently intense to 
use as a primary beam, as its great lonizing power in some 
degree compensated for the weakness of the radiation. It 
was, however, impossible to adopt the method employed with 
the more intense primary beams, as the ionization produced 
by what was in this case a tertiary radiation in electroscope 
M, in the position shown in the figure, was only a small 
fraction of the normal ionization when the electroscope was 
not in the path of any known radiation. Instead of placing 
the electroscope M so far away from the primary beam in 

a 
i 
4 
‘ 
