540 Dr. L. B. Loeb on the Recoil of 



through 105°. In column 4 is given the increase in the 

 number of particles for the deeper layers, caused by the loss 

 of velocity of the alpha particles in reaching those layers. 

 In column 5 are given the actual numbers to be expected 

 taking into account the figures in columns 2, 3, and 4. Not 

 much stress can be laid on the absolute values on account of 

 the uncertainty with regard to several of the factors involved. 



Table I. 



1. 2. 3. 4. 5. 6. 7. 8. 



Number Depth of Correction Ratio of A idal 



Substance P ei ' cm ; of penetration for depth Theoretical Observed obs> distance 



' deflecting (cm. air of number. number. -=- • in-lo 



material, equivalent), penetration. theory 1U cm. 



Carbon ... (M48 0-54 TOG 025 3*38 



Al 139 1-42 1-19 2-35 144 -613 6-96 



S 1-89 1-58 1-23 3-68 1*83 '497 8-43 



Cu 4-44 2-05 1-31 11 -9 5 -67 '476 14 6 



Ag 11-7 2-30 1-36 36-6 17*7 -484 26-5 



Au 1.8-8 2-47 1-43 666 31-6 '475 38"4 



Pb 19-6 2-47 1-43 69"3 323 -466 39-8 



Iii column 7 are given the ratios o£ the numbers observed 

 to those calculated, while in column 8 the closest distances 

 calculated on Darwin's theory between the centres of alpha 

 particles and atom (apsidal distance) for deflexions through 

 105°, after passing the mica window, are given. It is to be 

 observed that aluminium is the only element in which the 

 ratio above is abnormally high. Whether this lies within 

 the limits of experimental variation is not certain, but it 

 seems unlikely when one regards the variations of the ratio 

 for other elements. It is also significant that in aluminium 

 we have an element where the apsidal distance under experi- 

 mental conditions is about the value of the apsidal distances 

 found to give abnormal results by Prof. Rutherford. How- 

 ever, the counts for aluminium under these conditions are so 

 low that one cannot place too much confidence in so slight a 

 deviation. It seems likely that work at 170° would give 

 more satisfactory results. 



An experiment v^ as made to determine the range of these 

 alpha particles deflected by Al. The control gave 4*3 scin- 

 tillations per minute, using an absorbing sheet of 2'30 cm. 

 air equivalent of aluminium foil between the position of the 

 target and screen, and 36 mg. RaO. On putting in the 

 target the number per minute became 4'4. On removing 

 the alumimum absorbers with target in place the count rose 

 to 10*3 per minute. The 1'66 particles per 10 mg. deflected 

 by the aluminium were completely absorbed by the 2*3 cm. 

 of aluminium plus the 1*2 cm. absorption of the mica and 



