and the Gravitational Field. 061 



This thermodynamic relation between the energy of radio- 

 active disintegration and the gravitational potential does not, 

 however, exclude the possibility of a connexion of an 

 intimate character between, for example, the intensity of 

 the gravitational field and the rate of radioactive disintegra- 

 tion. It is the latter type of relation which the present 

 experiments have been designed to detect. 



According to Einstein's generalized theory of relativity, a 

 gravitational accelerational field is essentially the same as a 

 field of centrifugal acceleration. We have therefore tested 

 the effect due to a change in the gravitational field by 

 subjecting the radioactive material to a strong centrifugal 

 acceleration. It was obvious that the maximum centrifugal 

 acceleration which could be attained at the edge of a rotating 

 wheel would fall far short of the mean acceleration to which 

 the atomic nucleus is subject due to the thermal agitation of 

 the atoms. There was a chance, however, that a com- 

 paratively steady acceleration might have an effect different 

 from that of the rapidly varying molecular accelerations. 



The Experiments. — A small tube of radium emanation was 

 placed, in a hole near the circumference of a brass disk of 

 10 cm. radius. The gamma radiation from the emanation 

 was measured when the disk was rotating slowlv and when 

 turning at approximately 250 revolutions per second. The 

 acceleration was thus varied from about 1*5 to about 20,000 

 times the acceleration of gravity. 



The gamma radiation was measured by a balance method. 

 The ionization due to the gamma rays traversing a large 

 ionization chamber was balanced against an adjustable current 

 passing through a high resistance, a highly sensitive electro- 

 meter being used to detect any difference between the two 

 currents. For the high resistance a Bronson resistance was 

 at first employed. This was later discarded in favour of a 

 resistance consisting of lampblack on sulphur. The latter 

 resistance, though more subject to variations over long 

 periods, has the advantage that it introduces no short period 

 probability variations such as those due to the ionization by 

 discrete alpha particles when the Bronson resistance is used. 

 The probability variations in the ionization current due to 

 the gamma rays, such as have been observed by Meyer *, 

 Labyf and others, were very noticeable in these measure- 

 ments, and were the cause of practically the whole of the 

 <lifferences between successive measurements. 



Altogether four extended series of measurements were 



* Merer, Phys. Zeitschr. xi. p. 1022 (1910). 

 t Laby, ' Nature/ lxxxvii. p. 144 (1911). 



