SCIENCE AND PRACTICE. 423 



regard to the value obtained for the speed of speaking through 

 the new Atlantic cable =1-15 words per minute, this might 

 seem a direct contradiction to the assertion of Professor 

 William Thomson and Mr. Yarley, that they can telegraph 

 through the whole line at a rate of 8 words per minute. 

 The reason of this very augmented rate of working, is due 

 to the employment of a new transmitting apparatus, invented 

 by these two celebrated electricians. This apparatus consists 

 in a key so arranged as to send for each signal a series of 

 five separate waves of different lengths into the cable. The 

 first wave is positive, and lasts long enough to reach the 

 other end of the cable and move the receiving instrument, 

 immediately upon this succeeds a wave of shorter duration 

 from the negative pole, which wipes out the positive charge 

 and leaves it negative ; this wave is not intended to reach 

 the other end or give a signal. The third wave is again posi- 

 tive, it is cut off still shorter, and " wipes out " the negative 

 charge, and leaves the cable, towards the home end, positive. 

 The fourth wave is still shorter, negative, and so on. By 

 this means, by the time the complete signal or five decreasing 

 waves are given, each of which, except the first, is absorbed 

 in the next succeeding it, the cable is left in its normal 

 condition, and without the necessity of adopting any of 

 the contrivances explained in the first part, the corre- 

 spondence can be regularly proceeded with. 



