On the Conditions of Elicitation of Certain Eating Reflexes

The absorption coefficient of various substances for y-rays from ThC filtered through 6.8 cm. of lead is given in table B. The lead absorber is of 0.682 cm. thick, and the thickness of other absorbers is approximately equivalent to this. From the above table, it is seen that the value ue obtained by dividing the absorption coefficient . by the number of external electrons per cc., increases with the atomic number, while according to the theoretical formulae it should be constant. This might be explained by the following alternatives. (1) A part of the scattering may be due to electrons inside the nucleus as suggested by Professor Millikan in a report made to the National Academy in Nov., 1929, in which cosmic rays were shown to exhibit this same effect in still greater degree. (2) The scattering of a tightly bound electron of the atoms of high atomic numbers may be greater than that of a loosely bound electron. (3) There may still be some true absorption due to the photo-electric effect. At present, an investigation of the process of scattering is being carried on which might possibly throw some light on these questions. I should like to express my gratitude to Professor R. A. Millikan and Professor I. S. Bowen for the suggestion of this experiment and their help in carrying it through, and also to Dr. H. N. McCoy who helped with the preparation of the Radio-Thorium. * Research fellow of The China Foundation for the Promotion of Education and Culture.