534 Mr. Sidney George Brown . [March 12. 



sensitiveness of an ordinary metal balance that with S grrammes in 

 each pan mnst turn accurately with one inilligramme. 



I now illustrate the duplex with a mechanical model. 



It is now found necessary to maintain still more perfect balances 

 for our new method of " high-speed working of cables." — in fact, a 

 balance that must be maintained to within the proportion of 72,000 

 to 1. 



To do this the very greatest care has to be directed to questions 

 of insulation and temperature correction, and special appliances are 

 supplied to obtain this high degree of accuracy. In fact, the future 

 of " high-speed working of cabfes " is locked up very much with this 

 question of more delicate and accurate balances ; and if still more 

 perfect balances could be obtained, still higher working speeds of 

 cables would immediately be possible. 



I now come to the instruments employed to work the cables, 

 starting with the sending end. 



As "before pointed out, the various letters of the cable alphabet 

 are composed of combinations of + and - electrical impulses, or of the 

 records that these impulses produce. The letter e is a + impulse, t a 

 - one, a is composed of two impulses, a + and - and so on for all the 

 other letters. The operator has, therefore, first to translate the 

 message to be sent into the cable code, and then to tap on the sending- 

 key the order of the impulses that make up the code message. 



A sending-key consists of two levers : the depression by the finger 

 of either one or the other determines which end of the battery, the 

 + or - end, is joined to the cable. 



Sending messages by hand is open to two objections : one the 

 want of speed, the other the want of accurate spacing of the letters. 



A good trained clerk can send at the rate of about 140 letters per 

 minute ; but as most cables are capable of being worked at greater 

 speeds, automatic or machine transmission has now become universal. 



An automatic transmitter is an instrument that does the work of 

 the clerk in sending ; the two levers of the hand key are now operated 

 upon by mechanism driven by a motor, through the agency of a per- 

 forated ribbon. 



Everyone who is acquainted with the Pianola or Automatic Piano 

 Player knows that the music to be played is punched as holes in a 

 broad paper strip ; this strip is run through the machine and deter- 

 mines which levers are to press upon the keys of the piano. 



The operation of the automatic transmitter is precisely like this, 

 only instead of the extended keyboard there are two keys, a + and - , 

 and the paper strip is a narrow ribbon with only two rows of holes to 

 work the levers. 



To send a message, the clerk first of all by means of a hand per- 

 forator, punches the message as combinations of holes in the paper 

 ribbon : this ribbon, after being perforated, is fed through the auto- 

 matic transmitter. 



