192 RAY STANNARD BAKER 



the passage of the positive half of the alternating wave when 

 the current has started and maintained in that direction, and 

 of suppressing the other half; in other words, of changing an 

 alternating current into a direct current. In this process 

 there was a loss, the same for currents of all potentials, of only 

 14 volts. I have already spoken of the very great importance 

 of this invention. 



Following close upon the announcement of the new con- 

 verter, Mr. Hewitt found that his mercury tube could be also 

 transformed into a nearly perfect electrical interrupter. As 

 I have already shown, the mercury vapor opposes a high re- 

 sistance to the passage of electricity until the current reaches 

 a certain high potential, when it gives way suddenly, allowing 

 a current of low potential to pass through. This property 

 can be applied in breaking a high potential current such as is 

 used in wireless telegraphy, so that the waves set up are ex- 

 actly the proper lengths, always accurate, always the same, 

 for sending messages through space. By the present method 

 an ordinary arc or spark gap — that is, a spark passing between 

 two brass balls — is employed in sending messages across the 

 Atlantic. Marconi uses a spark as large as a man's wrist, 

 and the noise of its passage is so deafening that the operators 

 are compelled to wear cotton in their ears, and often they 

 must shield their eyes from the blinding brilliancy of the dis- 

 charges. Moreover, this open air arc is subject to variations, 

 to great losses of current, the brass balls become eroded, and 

 the accuracy of the transmission is much impaired. All this 

 is obviated by the cheap, simple, noiseless, sparkless, mer- 

 cury bulb. 



"What I have done," said Mr. Hewitt, "is to perfect a 

 device by means of which messages can be sent rapidly and 

 without the loss of current occasioned by the spark gap. In 

 wireless telegraphy the trouble has been that it was difficult 

 to keep the sending and the receiving instruments attuned. 

 By the use of my interrupter this can be accomplished." 



And the possibilities of the mercury tube, indeed of in- 

 candescent gas tubes in general, have by no means been ex- 

 hausted. A new door has been opened to investigators, and 

 no one knows what science will find in the treasure house — ■ 



