different Metals by Rontgen Mays. 297 









Table 



VIII. 















•001 



•002 



•003 



•004 



•008 



•012 



I 



3-4 



6-8 



1-8 



2-6 



3-8 



4-8 



5-2 



II 



3'8 



7-8 



2-0 



2-8 



3-4 



5-0 



5-4 



III 



4-0 



7-6 



2-0 



3-2 



4-4 



5-8 



6-6 



Average 



3-73 



7-40 



1-93 



2-86 



3-86 



5-2 



5-7 



Ratio 



1-00 



0-50 



0-29 



0-19 



0-14 



0-11 



o-io 



Table 8 has been inserted to give an idea of the actual obser- 

 vations as taken. It is for tin for a hardness of the primary 

 rays of 095. The numbers in the top row give the thickness 

 of aluminium in millimeters. The next three rows give the three 

 sets of observations of the time in seconds for the gold leaf to fall 

 over a constant number of scale divisions ; these values being 

 inversely proportional to the intensity of ionization. The gold 

 leaf moved so rapidly for the unabsorbed rays and so slowly 

 after the rays had been partially absorbed that the same num- 

 ber of scale divisions could not be used for all thicknesses of 

 aluminium. The times in the first two columns are for a fall 

 of forty scale divisions, while in the remaining five columns 

 the times are for a fall of five scale divisions from the same 

 zero point. A separate observation showed that for a constant 

 intensity of ionization the fall for forty divisions was to the 

 fall for five in the ratio of 6*7 to 1. The last row gives the 

 ratio of intenshvy of ionization to the initial intensity after 

 reducing the times of fall to the same number of scale divi- 

 sions. It was found that owing to asymmetry of. the appa- 

 ratus a very small change of hardness in the primary rays 

 would disturb the balance enough to account for a large part 

 of the errors, though great care was taken to see that the ioni- 

 zation due to the primary rays was properly balanced out before 

 each separate observation. To show the magnitude of this error, 

 suppose that the time observed for the secondary rays to pro- 

 duce a fall of five scale divisions was five seconds, it was some- 

 times found that after an observation the balance had been 

 disturbed sufficiently for the primary rays alone to produce a 

 fall one way or the other of five divisions in eighty seconds, 

 which would tend to make the fall observed for the secondary 

 rays too large or two small by about 6 per cent. 



After this investigation of the character of the secondary 

 rays coming off from different metals, the way was open to 

 obtain some idea of the relative number of corpuscles produced 

 in different metals for equal absorptions of the primary Ront- 

 gen rays. The method of procedure was nearly the same as 

 that already described. The absorption curves showed that 

 essentially all the corpuscles were stopped in the first -003 mm 

 to -004 rDm of aluminium, while practically all the secondary 



