THE VACUUM THERE 's SOMETHING IN IT WHITNEY 197 



quality of its vacuum determine the death or limit the performance 

 of a lamp. But while formerly the incandescent lamp represented 

 the very highest skill then reached in vacuum production, there are 

 now other commercial vacua which are necessarily quite superior. 

 This is true of good thermos bottles, X-ray tubes, and radio tubes. 



We should first, therefore, give brief consideration to the incan- 

 descent lamp and note a few characteristics. Its Ioav vacuum early 

 disclosed electric cross currents which would not have been found in 

 much higher vacua. Study of these currents has led not only to the 

 vacuum tubes used in radio, but also to such remote disclosures as 

 that distillation or evaporation of solids in vacuum proceeds in 

 straight lines. The electrical currents in poor vacua are best known 

 in luminous Geissler tubes, Moore tubes, and Claude tubes, as seen 

 on the streets of Paris, for example. They are themselves a large 

 subject, but consideration will be given (later on) only to one his- 

 torically important experiment with them, the Hittorf experiment. 



HIGH VACUA 



Electric currents through vacua, where gas is so completely re- 

 moved that it has no appreciable action, are most strictly a part of 

 this article. After the work by which the individual and indivisible 

 negative electrical charge or electron was defined, it seemed quite 

 fitting, though unexpected, to learn that these negative charges were 

 exuded by hot bodies. The result of this disclosure formed the basis 

 for most of the modern electrical phenomena in vacua. The activi- 

 ties of electrons are apparently the cause of most electrical and chem- 

 ical processes. Their motion constitutes electric currents, and the 

 currents are determined and controlled by voltage or potential dif- 

 ference. 



Bees might illustrate electronics, though it's admittedly bad policy 

 to push bees too hard. II bees represent electrons, then matter in 

 general becomes the hives. When the hives are cold or in the dark 

 the bees stay inside. Under the effect of heat or light the bees are 

 induced to come out. Similarly highly heated matter, such as tung- 

 sten, exudes electrons; and at ordinary temperatures light induces 

 electrons out of metallic potassium, for example. 



What are the bees or electrons going to do after they are out of 

 the hive (or the metal) ? That depends on imj)ulse or pressure. 

 They will fly in that special direction which tends to relieve that 

 particular pressure. They proceed down the gradient. The electrons 

 coming out of the metal (because of heat or light) will also fly in 

 that special direction which will tend to relieve the particular elec- 

 trical pressure. They also proceed down the gradient. But if there 



