68 nature's 



great practical value of energy in this form is 

 that it can be distributed through a conductor 

 economically for many miles. We can trans- 

 mit mechanical power by means of a rope or 

 cable for a limited distance, but at tremendous 

 loss through friction. We can transmit power 

 through pipes by compressed air or steam, but 

 there is a great loss, especially in the case of 

 nteam, by condensation from cold. None of 

 Ihese methods are available for long distances. 

 Another advantage electricity has over other 

 forms of energy is the speed with which it 

 can be transmitted from one place to another. 

 In this respect it has no rival except light. 

 But we have not been able to harness light and 

 make it available to carry either freight or 

 news, except in the latter case for a short dis- 

 tance by flashing it in agreed signals. 



The heliostat can be used when the sun 

 shines to transmit news by flashes of sunlight 

 chopped up into the Morse code and thrown 

 from point to point by a moving mirror. But 

 this is limited as to distance; besides, the sun 

 does not always shine. It has the disadvantage 

 in thatrespect that the old semaphore-telegraph 

 did that was in use in Wellington's day. These 

 semaphores were constructed in various ways, 

 but a common form was that of moving arms 

 that could be seen from hill to hill or point to 

 point. By a code of moving signals news was 

 repeated from point to point and it can be 



