204 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1924 



metals. Referring again to our bee analogy, let a fast flying swarm 

 strike bells so hard that they make them ring. From the sound or 

 musical notes we guess roughly the sizes of the bells. We could thus 

 place them in their musical series. The sound corresponds to the 

 X rays produced when the bees are electrons of cathode rays and 

 sound waves are ether waves. The mass of the bell is disclosed by 

 the tone or frequency; the mass of the atom, by the same sign, is 

 disclosed by the ether wave frequency. Wlien a certain mineral was 

 used as a surface for the electrons to hit, a new musical note in the 

 ether was found. It was recorded photographically. Its place in 

 the scale of elements had been predicted as accurately as middle C 

 on the piano might have been predicted if it had never been heard. 

 With higher voltages the velocity of the cathode rays (or elec- 

 trons) always increases. In the X rays thus far produced, however, 

 the penetration or transparency is practically limited to about a 

 quarter of an inch of lead. It is interesting to note that the similar 

 rays from radium, the so-called gamma rays, can penetrate nearly 

 a foot of lead. This corresponds to an exceedingly high electro- 

 motive force. Thus radium rays (gamma rays) might be made in 

 vacuum X-ray tubes if millions of volts were applied. 



ATOM LAYERS 



The apparatus shown in Plate 4, Figure 2 (devised by Doctor 

 Hull) is essentially a two-electrode vacuum tube, the tungsten fila- 

 ment having a little thorium in it. At a certain very high tempera- 

 ture this thorium rapidly diffuses to the filament surface. This 

 thorium surface then has the peculiar power of emitting electrons a 

 hundred thousand times as rapidly as pure tungsten at the same 

 temperature. An ordinary lamp may be lighted in this experiment 

 by letting this thorium electron-emission current flow through the 

 lamp filament. The vacuum tube containing the thorium-coated 

 tungsten also contains a little gas. When the lighted lamp is short 

 circuited for an instant by a switch, the potential on the vacuum tube 

 is thereby greatly increased, and this causes positive ion bombard- 

 ment of the filament and thus tears the thorium all off the tungsten 

 surface, so that very few electrons are being emitted, that is, those 

 characteristic of pure tungsten at that temperature. Then the load 

 (the lamp) can no longer be carried by the electron current. To 

 repeat, the heavy positively charged gas ions under the impulse of 

 the raised electrical potential act like a powerful sand blast and 

 effectively clean the thorium from the tungsten, thus greatly re- 

 ducing the emission current. By highly reheating the filament for 

 a few seconds only, a fresh layer of thoriiun may be diffused to the 

 surface of the filament from within the tungsten, so that then at the 



