ADAMS. — TRANSMISSION OF IlUNTGEN RAYS. G03 



the plienomena observed with dilFerent thicknesses of one metal are 

 concerned. 



Another explanation of the phenomena of transmission has recently 

 been proposed by Walter. ^^ His theory assumes that the effect of 

 transmission through any substance upon a beam of rays, which may be 

 supposed homogeneous, is essentially a transformation of the character 

 of the beam, — a transformation which in some way renders the rays 

 more penetrating toward all substances. In particular, transmission 

 through a piece of silver, cadmium, or tin is assumed to render the rays 

 especially penetrating toward another piece of either of those metals, 

 and the more so as the atomic weights of the two metals concerned 

 are more nearly equal. These assumptions are a necessary consequence 

 of his experimental results, which are briefly as follows : The pene- 

 trating power of the rays direct from the tube was compared with the 

 penetrating power of the rays after transmission through a sheet of silver. 

 The comparison was made by the use of the Benoist- Walter scale of 

 hardness ^^ and a photographic plate. It appeared that the rays were 

 rendered less penetrating by transmission through the silver. Trans- 

 mission through cadmium and through tin showed the same effect to 

 a less extent. The effect of transmission through each of the three 

 metals was also examined by means of scales of hardness in which the 

 central disk of silver was replaced by one of cadmium or by one of 

 tin ; in every case it was found that the greatest reduction of pene- 

 trating power occurred when the central disk of the scale was of the 

 same metal as the interposed sheet, and that this reduction of 

 penetrating power diminished as the atomic weight of the metal of 

 the disk departed from that of the metal of the interposed sheet. 

 Transmission through sheets of metals other than silver, cadmium, or 

 tin appeared in all cases to increase the penetrating power of the 

 rays as measured by either of the three scales of hardness. A dif- 

 ferent series of experiments with the fluoroscope indicated that the 

 anomalous reduction of penetrating power by transmission through 

 silver, cadmium, or tin was apparent rather than real, and that in 

 every case the effect of transmission through one metal was to in- 

 crease the penetrating power of the rays for every metal. This result, 

 if correct, makes untenable an hypothesis of relative selectivity in the 

 absorption of the rays by different metals, which otherwise might 

 explain the experiments with the scales of hardness, and renders 

 necessary some such theory as the one which Walter proposes. 



" B. Walter. Ann. d. Pliys., 17, 5G1 (1905). 

 " B. Wiiltor, loc. cit. 



