198 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1924 



is no particular impulse or gradient, both bees and electrons hang 

 around the source. 



A lot of electrons, like bees, flying in a common direction, becomes 

 a current or cathode ray. We might let them fly from the hot or 

 lighted spot into a cold or dark one, and until we heated or lighted 

 the latter they would not come out. This unidirectional current cor- 

 responds to what takes place in rectifiers and kenotrons, where we 

 have impulses in two opposite directions between one hot and one 

 cold electrode in vacuum. If the hives (or the electrodes) are equal 

 in temperature or illumination, no differential in current is possible, 

 and with alternating impulses alternating instead of pulsating direct 

 current passes. Thus bees illustrate two-electrode vacuum devices. 



In the three-electrode vacuum tubes the third electrode is a sort 

 of grid, or open fence, located between the hot and cold electrodes. 

 This grid lets electrons pass freely, except when it is negatively 

 charged. Thus also the bees would pass through a wire fence when 

 they might be stopped if their impulse to proceed could be suddenly 

 removed there. The negative charge is used in the three-element 

 tube to alter the intention of the migrating bees or electrons as often 

 as desired, and this with the rapidity of light. 



In the case of radio, it is the impulse from the antenna or loop, 

 changing with every delicate change of voice-current or code-cur- 

 rent, which, when led to the grid, charges it and thus controls the 

 currents within the receiving tube. These controlled currents do 

 the work in the telephone. 



Everybody knows that radio tubes are very sensitive. One cat- 

 power of electricity used in New York actually puts the impulses 

 into a receiving outfit in San Francisco, and at the same time it also 

 puts the identical impulses into millions of other receivers. But 

 some appreciable energy must be used by each receiver to direct the 

 local battery which operates the head sets. This minute quantity 

 of energy may be made significant as follows : 



If a house fly climbs up a window pane 1 inch, he does a definite 

 amount of work in lifting his body that much. If this work con- 

 stituted the supply fed into the receiving tube from space, it would 

 suffice to actuate the outfit continuously for a quarter of a century. 

 This might interest a future student of telepathy, if the time comes 

 to determine how far the energy of one thought may influence 

 thought in a distant brain. It has not been possible thus far to 

 determine the quantity of energy which is expended in thought. 

 Just keeping alive transfers so much energy into heat that the addi- 

 tional energy transferred when we think has been too small to detect. 

 But it need not be small compared to the power sensitivity of a 

 radio set. 



