Rollins — Cathode Stream, and X- Light. 391 



enough difference to account for aluminum being forty times 

 as transparent as platinum. As we do not find enough differ- 

 ence in the amount of interatomic ether to account for the 

 difference in transparency, we must give up the solid atom 

 theory, for it fails here as it does in attempting to explain the 

 cathode stream. Both phenomena require a compound atom. 

 But the cathode stream theory, that the particles into which 

 the atoms are broken are the ultimate units, cannot be true, for 

 they have a familiar spectrum. A theory of the atom must 

 meet these difficulties. The following is suggested. The atom 

 is made of sub-atoms. The sub-atoms are the cathode stream 

 particles. There are as many kinds of sub-atoms as there are 

 elements. We should expect the cathode stream particles, 

 therefore, to have familiar spectra. The sub-atoms are com- 

 pounds. They are made of the ultimate units of which the 

 elements are composed. These ultimate units have the same 

 size and weight. As the atoms have the same size and dif- 

 ferent weights, light atoms must contain fewer ultimate units 

 than heavy ones. There would be more space filled with ether 

 in a light than in a heavy atom. When an electromagnetic 

 phenomenon passes through an atom of a conductor, it can 

 only travel in the contained ether, for this is the only trans- 

 parent part. The atom with the most ether would be most 

 transparent. Aluminum having more ether and fewer opaque 

 particles, would be more transparent than platinum. Apply 

 this theory to the following experiment, intended to show that 

 the transparency of aluminum is not the only reason why 

 aluminum is less efficient for a target in an X-light tube than 

 platinum. I made a tube with the usual platinum target, cov- 

 ered with a thin veneer of aluminum on the surface struck by 

 the cathode stream. Had the transparency theory been the 

 true explanation, such a target should have acted toward 

 X-light about as a glass mirror, silvered on the back, would 

 have to ordinary light. As the X-light passing through the 

 aluminum struck the platinum, only a little more could have 

 been lost than with a target entirely of platinum. I never made 

 an efficient X-light tube in this way. The following expla- 

 nation was given. When a cathode stream particle strikes an 

 aluminum target it is not so abruptly stopped as by a heavier 

 metal. The heat of impact is not so high, the energy con- 

 version extending over a longer time. The particles must be 

 less efficient sources of X-light, if this is due to a high tem- 

 perature. But why should a heavy metal target stop a flying 

 particle more abruptly than a lighter one ? I made this 

 answer. Aluminum on the compound atom theory given is a 

 more open structure than platinum : on this account it would 

 stop a flying particle less abruptly. 

 September 28th. 



Am. Jour. Sci. — Fourth Series. Vol. X, No. 59. — November, 1900. 

 26 



