464 An Experiment relating to Atomic Orientation. 



effect has been found, but even a negative result may be of 

 some interest, since it would appear to show that one or both 

 of the assumptions are incorrect. The experiments need only 

 be very briefly described. It is in the first place necessary 

 to choose a substance whose disintegration products would not 

 contribute appreciably to the radioactivity under the par- 

 ticular conditions o£ measurement which are adopted, as it 

 is obviously unreasonable to expect that an atom should 

 remain unaltered as regards its orientation after a cataclysm 

 which has changed it into a new substance to which the 

 arrangement of the neighbouring atoms in the crystal is no 

 longer a natural one. After a number of trials with sub- 

 stances and by methods which were for various reasons 

 unsuitable, the experiment was tried with some large crystals 

 of uranium nitrate which were specially grown for the 

 purpose. The « ray activity was measured by means of an 

 electroscope essentially similar to the well-known instrument 

 designed by Sir Ernest Rutherford for the measurement of 

 Aveak a. ray activities. Holes were drilled through the top 

 of the electroscope, these holes being smaller than the 

 smallest face of the crystals, and comparison was made of 

 the rate of leak of the electroscope without the crystals, and 

 with the three different faces of the crystals respectively 

 placed over the holes. The crystals were removed from the 

 solution in which they were growing and dried immediately 

 before each experiment, with a view to avoiding as far as 

 possible changes in the surface through exposure to the 

 atmosphere. The radioactivity of the c^stals measured in 

 this way was found to be independent of the face from which 

 the a. rays Avere emitted, the accuracy of agreement being 

 about 3 per cent. This was within the limit of experimental 

 error, and the differences in the readings w T ere not in any 

 way systematic. 



0}'sta]s of uranium nitrate appear to offer a very 

 favourable material for the experiment from the radio- 

 active characteristics of the uranium atom, and also pro- 

 bably from a crystallographic point of ah*tw; they contain of 

 course the two isotopic uraniums, but the ft rays from the 

 disintegration products are negligible in so far as the u ray 

 activitv measured in this way is concerned. The expe- 

 riment might be worth repeating under conditions in which 

 the j3 rays from different faces are compared. A probable 

 explanation of the failure to obtain a positiA r e result is that 

 the a ravs are shot out from the nucleus without regard to 

 the orientation of the atomic axis. 



Balliol College, 

 Oxford. 



