December 13, 1912] 



SCIENCE 



837 



two. These are lighted constantly. Another 

 four-candle lamp is connected with the regu- 

 lator. These are placed in an ashestos-lined 

 box beneath the bath. The whole apparatus 

 surrounded with non-conducting material is 

 packed in a box with a hinged cover. The 

 only surface exposed when the box is opened 

 is the top of the bath. Thick pads cover the 

 moat, as it is lower than the top of the bath. 

 This makes it possible to heat eight cups of 

 paraiEn, using at the same time less current 

 than would be used by a single sixteen-candle 

 incandescent lamp. Taking out from or put- 

 ting into the regulator a small drop of mer- 

 cury makes it possible to either raise or lower 

 the temperature of the bath. Old lamps can 

 be taken out and new ones put in through 

 holes in the bottom of the box. 



Such a bath has been in use more than a 

 month, maintaining a temperature constant 

 (54° C.) to within a fraction of a degree. 

 Webster Chester 



CoLBT College, 

 Waterville, Me. 



A SIMPLE discharge TUBE FOR DEMONSTRATION 

 PURPOSES 



At the present time when so much interest 

 is centered on electric discharge phenomena 

 in evacuated tubes it may not be out of place 

 to describe one of the discharge tubes that the 

 writer used recently for class-room demonstra- 

 tion. The experiment is purely qualitative, 

 and in principle contains nothing new. Its 

 aim is to present with simple and easily con- 

 structed apparatus some of the phenomena 

 that are usually given with more elaborate and 

 expensive outfits. It does, however, require 

 that the experimenter have access to, and be 

 familiar with, the operation of an ordinary 

 Geissler mercury pump and an induction coil. 

 Aside from these the things needed are found 

 in almost any laboratory and require no more 

 skill to make than the blowing of a glass Tee. 



The discharge tube in question is shown in 

 the figure. The bulb may well be a two- or 

 three-liter florence flask. The part to be 

 blown is MN. It supports the aluminum rod 

 carrying at its upper end the spherical or 



oblong cathode, C, of the same metal. The 

 anode, A, is a cylinder of not too light weight 



aluminum foil placed in the neck of the flask 

 as shown. Connection to this is made by a 

 fine copper wire led out through the wax joint, 

 BW, at the mouth of the fl.ask. The exhaust 

 tube should contain a glass valve and ter- 

 minate in a sort of ball and socket joint (to be 

 sealed with wax) so that the apparatus may 

 be readily disconnected from the pump. The 

 charcoal bulb, CB, may be dispensed with 

 where liquid air is not available. Liquid air 

 is not a necessity; its use, as is well known, is 

 to hasten the exhaustion. The three joints, 

 RW, may be closed sufficiently air-tight by a 

 good grade of red sealing wax. 



The various steps, as the exhaustion pro- 

 ceeds, may be vividly shown — ^the stringy dis- 

 charge, the Geissler stage, the formation of 

 strise, the Faraday dark space followed by 



