344 SCIENCE OF HOME AND COMMUNITY 



tain it, as it requires fewer employees and there is not so 

 much outfit to keep in repair. There would be fewer break- 

 downs, as there would be no wires to be exposed to storms, 

 and the breakdowns that did occur could be more easily 

 found and repaired. And furthermore, it transmits speech 

 more distinctly and perfectly. 



Disadvantage of wireless. The wireless telephone has one 

 great disadvantage, however. It is found that the efficiency 

 of its working varies from day to day, owing to natural elec- 

 trical disturbances. This does not matter so much for short 

 distances ; but for long distances it is a serious matter, 

 since unfavorable conditions may prevent the telephone 

 from working at all. It is not possible now to use the wire- 

 less in cities where there are many telephones in close prox- 

 imity. It does not seem probable that wireless will take 

 the place of wire telephone for local use. 



Construction and operation of wireless telephone. We may 

 next inquire regarding the construction and method of 

 operation of this wonderful instrument that can send the 

 human voice across the ocean. There are three essential 

 parts to a wireless telephone : first, a machine to start waves 

 in the ether ; second, a device by means of which the voice 

 can control these waves ; and third, a receiver for detecting 

 the waves and changing them into sound. 



There is the same difference between the wireless tele- 

 phone and telegraph that there is between the ordinary 

 telephone and ordinary telegraph. In both telegraphs the 

 circuit is interrupted by means of a key. In both telephones 

 there is a continuous current, and connected with this is a 

 telephone transmitter. 



. A number of different devices have been used, but we will 

 undertake to understand only the general principle. The 

 human voice, by means of the air waves, sets the diaphragm 

 of the telephone into vibration. As this disk vibrates, it 

 causes a change in the current. This varying current is 



