1880.] on the Tclegra^liic Achievements of Wheatstone. 299 



that a double-needlo instrument was capable of meeting all require- 

 ments, and here before you are instruments of the original design on 

 the double-needle principle. This one of an elegant architectural . 

 design was made for use in the New House of Parliament about 1850. 

 Before you are the first two double-needle instruments that were ever 

 used, and they are greatly prized for their historical value. This 

 kind of instrument met the same fate as its predecessors, and was 

 superseded by a single-needle instrument which gave out its signals 

 quite as efficiently as its earlier brethren possessing a greater number 

 of needles. This form has remained in use to the present day, and 

 may be seen at any railway station in the country. It is used to a 

 greater extent than any other kind of tclegraj)h instrument, there 

 being at the present moment at least 10,000 employed by railway 

 companies, and 3500 by the Post Office. It is an instrument of 

 simple construction, but I will not detain you by explaining details. 

 You can easily see that when I press down a pedal the needle is 

 deflected ; if it be the right-hand pedal then the needle goes to the 

 right, and if the left-hand pedal it goes to the left, and one deflection 

 to the left and one to the right represents the letter A, one to the 

 right and three to the left B, four beats, viz. one right, one left, one 

 right and one left C, and so on through the alphabet. 



Wheatstone saw the necessity of doing away with the trouble of 

 acquiring familiarity with this kind of instrument, and set to work to 

 introduce one which could be understood by anyone in a moment's 

 acquaintance. This, of course, meant representing the ordinary 

 letters of the alphabet without requiring translation from signals. 

 He produced an instrument which printed the ordinary letters, but 

 the mechanical complexity of its arrangement compelled him to 

 abandon it. He then thought of a permanent alphabet on a dial 

 which revolved in front of an open window or around which the 

 indicating needle could revolve and point out the exact letters sent. 

 This proved more practicable, and the result was the alphabetical 

 instrument, such as I now show you. The indicating portion works 

 in a very similar manner to the second hand of an ordinary clock. 

 In a clock the hand makes a slight pause at each point representing 

 a second on its dial, and proceeds by jerks round and round the dial, 

 being stopped at each second by the cogs of a wheel. The hand or 

 indicator of an alphabetical instrument works round the dial con- 

 taining the alphabet just in the same way, but is controlled by a 

 piece of mechanism which only answers to the current being sent. 

 Each current moves the mechanism to which is attached the indicating 

 needle, and each movement jerks forward the needle one step as it 

 were. To cause the needle to make one revolution round its dial we 

 will suppose requires fifty-two steps (really it is many more). Then 

 if it is made to wait or rest at every second step, and opposite that 

 step a letter is placed, it is easy to see that in one revolution all the 

 letters may be successively indicated. The indicator is caused to 

 rest or wait by the depression of small keys placed round the dial of 



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