Nikola Tesla - Free-Energy Devices

man FEEQUENCT AND HIGH POTENTIAL CUERENTS. 271should be larger,else it would be apt to get too hot, and thephosphorescence would cease. In this arrangement usually onlythe small bulb shows phosphorescence, as there is practically nobombardment against the outer globe. In some of these bulbsconstructed as illustrated in Fig. 157, the small tube was coatedwith phosphorescent paint, and beautiful effects were obtained.Instead of making the inside bulb large,in order to avoid undueheating, it answers the purpose to make the electrode m larger.In this case the bombardment is weakened by reason of thesmaller electric density.Many bulbs were constructed on the plan illustrated in Fig.158. Here a small bulb Z>, containing the refractory button >//,upon being exhausted to a very high degree Avas sealed in a largeglobe L, which w T as then moderately exhausted and sealed off.The principal advantage of this construction was that it allowedof reaching extremely high vacua, and, at the same time of using alarge bulb. It was found, in the course of experiments withbulbs such as illustrated in Fig. 158, that it was well to makethe stem *,near the seal at would be impaired in a comparatively short time.The chief idea in the two last described constructions was toconfine the heat to the central portion of the globe by preventingthe exchange of An air. advantage is secured, but owing to theheating of the inside bulb and slow evaporation of the glass, thevacuum is hard to maintain, even if the construction illustratedin Fig. 157 be chosen, in which both bulbs communicate.