42 Professor J. A. Fleming [Feb. 14, 



conclude that the material of which the plate is made is without 

 influence on the result, and this is found to be the case. Many of 

 the foregoing facts were established by Mr. Preece as far back as 

 1885, and I have myself abundantly confirmed his results. 



We should expect also to find that the larger we make our plate, 

 and the nearer we bring it to the negative leg of the carbon, the 

 greater will be the current 23roduced in a circuit connecting this plate 

 to the positive terminal of the lamp. I have before me a lamp with 

 a large plate placed very near the negative leg of the carbon of a 

 lamp, and we find that we can collect enough current from these 

 molecular charges to work a telegraph relay and ring an electric bell. 

 The current which is now working this relay is made up of the 

 charges collected by the plate from the negatively-charged carbon 

 molecules which are projected against it from the negative leg, across 

 the highly perfect vacuum. I have tried experiments with lamps in 

 which the collecting plate is placed in all kinds of positions, and has 

 various forms, some of which are here, and are represented in the 

 diagrams before you ; but the result may all be summed up by saying 

 that the greatest effects are produced when the collecting plate is as 

 near as possible to the base of the negative end of the loops, and, as 

 far as possible, encloses, without touching, the carbon conductor. 

 Time will not permit me to make more than a passing reference to 

 the fact that the magnitude of the current flowing through the 

 galvanometer when connected between the middle plate and the 

 positive terminal of the lamp often "jumps" from a low to a high 

 value, or vice versa, in a remarkable manner, and that this sudden 

 change in the current can be produced by bringing strong magnets 

 near the outside of the bulb. 



Let us now follow out into some other consequences this hypothesis 

 that the interior of the bulb of a glow-lamp when in action is pojju- 

 lated by flying crowds of carbon atoms all carrying a negative charge 

 of electricity. Suppose we connect our middle collecting plate with 

 some external reservoir of electric energy, such as a Leyden jar, or 

 with a condenser equivalent in capacity to many hundreds of Leyden 

 jars, and let the side of the condenser which is charged positively be 

 first placed in connection through a galvanometer with the middle 

 plate (see Fig. 10), whilst the negative side is placed in connection 

 with the earth. Here is a condenser of two microfarads capacity so 

 charged and connected. Note what happens when I complete the 

 circuit and illuminate the lamp by passing the current through its 

 filament. The condenser is at once discharged. If, however, we 

 repeat the same experiment with the sole difference that the nega- 

 tively charged side of the condenser is in connection with the middle 

 plate then there is no discharge. The experimental results may be 

 regarded from anotlier point of view. In order that the condenser 

 may be discharged as in the first case, it is essential that the 

 negatively charged side of the condenser shall be in connection with 

 some part of the circuit of the incandescent carbon loop. This ex- 



