Deflexion of a Particles through Large Angles. 

 Table VI. 



619 



Variation of Scattering with Atomic Weight. (Collected 

 results using Radium emanation.) 



I. 



Substance. 



II. 



Air equiva- 

 lents of foils 

 vised. 



III. 



Total number 

 of scintilla- 

 tions counted 

 for each 

 substance. 



IV. 



dumber N of 

 scintillations 

 at same angle 

 and for same 

 air equivalent. 



V. 

 A 32 ' 



YI. 



NXA 2 '' 3 



Gold 



Platinum 



Tin 



Silver 



Copper 



•52, -68 

 •54, -625 

 •51, 1-15 



•38, -435 

 •495, -61 

 •45, -52, 1-06 

 •55, "57 



1200 

 1000 

 1400 



600 

 1300 

 1600 



400 



2400 



2900 



1290 



1060 



570 



151 



57 



2770 

 2730 

 1300 

 1120 



507 



144 

 41-6 



•85 

 1-05 

 •99 

 •95 

 1-12 

 1-05 

 1-37 



Aluminium ... 



Note 2. — Introducing the new data for the mass per unit area of foils; 

 of the same air equivalent, as in note 1, the following- are the values 

 for the ratio of the scattering per atom divided by A 2 : — Au 3*1, Pt 3*4 r 

 Sn 3-4, Ag 3-4, Cu 3-95, Al 3-4. 



It will be seen from the table that, although the experi- 

 mental conditions were very different from those in the 

 previous experiments, the results are similar, and indicate 

 the essential correctness of the assumption that the scattering 

 per atom is proportional to the square of the atomic weight. 

 The deviations from constancy of the ratio (see notes 1 and 2) 

 are nearly within the experimental error. 



The measurements have not so far been extended to sub- 

 stances of lower atomic weight than carbon. When the 

 atomic weight is small and comparable with the mass of the 

 a particle, the laws of scattering will require some modification 

 to take into account the relative motion of the atom itself 

 when a collision occurs. 



Variation of Scattering with Velocity. 



In order to determine the variation of scattering with 

 velocity the apparatus was somewhat modified. A conical 

 glass tube coated with active deposit was again used as source 

 of radiation. This source was placed about 1 mm. from the 

 mica window (E, fig. 3), so that it was possible to insert 

 additional sheets of mica between the source and the window 

 to reduce the velocity of the a particles. Mica sheets were 

 used for this purpose on account of their uniformity of 



