4 Sir Oliver Lodge on the Mode of Conduction in Gases 



the projectiles radiate divergently so that they become places 

 o£ minimum bombardment ; while the interior hollow space 

 is filled with light, — the carriers there delivering up their 

 charges, or remaining long enough to have it bombarded out 

 of them by the electrons. 



A " valve " is a contrivance which permits the passage of 

 electricity in one direction only, or at least very much more 

 readily in one direction than the opposite. The special 

 feature or desideratum of anything which is to act as a valve, 

 therefore, is to have one terminal situated so that it can fire 

 down a constricted space and stop any procession coming along 

 it, while the other terminal should be in a roomy chamber ; 

 moreover this latter terminal should have points or edges 

 whence the bombardment will be diffuse. It may likewise 

 have interstices or hollow spaces wherein the bombardment, 

 apart from the presence of positive carriers, would be either 

 weak or non-existent. It should have no part of its surface 

 arranged so as to fire down the tnbe leading to the other 

 terminal, but free and open means of access should be pro- 

 vided in every direction. In other words, one terminal 

 should be near the centre of a large bulb, while the other 

 terminal is in a narrow tube. 



"With such an arrangement the constricted terminal can 

 easily act as anode and supply the current to the other one; 

 but if it is made to act as cathode, its cannonading activity 

 stops the advancing carriers and checks the current almost 

 entirely. It will also heat and crack the glass unless suitable 

 precautions are taken. . 



Although it is thus easy to understand the principle upon 

 which valves are based, it is not at all easy to construct them 

 so that they shall work well and permanently; many things 

 may go wrong, and a good deal of experience is needed for 

 their manufacture and right exhaustion. Every valve ought 

 to be tested and adjusted, if it is to be satisfactory. At 

 present they are made forme by Mr. Cossor in London and 

 tested in my laboratory. 



Illustrative Experiment. 



Selected out of a great number of experiments, the following 

 sample may serve compactly to illustrate the principles here 

 laid down : — 



A tube was made in accordance with the drawing, a 

 supplemental path being provided with a tap, the terminals 

 being A and B ; and with it the following tests were 

 made — 



