112 Mr. Mitchell on the Electric Telegraph. 



three. All the different methods were classed under three varieties, namely 

 the needle, the printing, and the step-by-step telegraphs. The signals by 

 the first method are produced by the deflection of one or more needles ; the 

 second prints as well as transmits messages ; and the third employs a 

 revolving pointer to indicate letters or signs upon a dial. The telegraph 

 commonly in use is the double-needled one, invented and patented by Cook 

 & Wheatstone. The construction of this instrument having been described, 

 and its operation illustrated by the transmission of messages betwixt two 

 machines in different parts of the hall, Mr. Mitchell pointed out the 

 principal defects of this method, as consisting in the expense caused by 

 the necessity for having three wires, and in the liability of the wires to 

 come into contact with each other. This is a contingency of such frequent 

 occurrence as to require the constant employment of several men to 

 separate the wires when the contact takes place. Another inconvenience 

 arises from the difficulty of attaining perfect insulation of the wires. 

 In wet weather it often happens that all the wires become connected 

 electrically at the posts, by the -water passing from one wire to another. 

 What is still required, then, is an instrument combining cheapness with 

 accuracy and rapidity. When this has been attained, the use of the electric 

 telegraph will be brought within the reach of all classes of the community. 

 At present the high charge for transmitting intelligence limits its useful- 

 ness for the purposes of trade and commerce. In America the telegraph 

 is much more accessible. A message which would there be sent for several 

 hundred miles, at the charge of half a dollar, would, in this country, cost 

 nearly four dollars, or eight times more. In the United States there are 

 about 9000 mUes of telegraph ; in England between 2000 and 3000 ; in 

 Scotland only about l(jO miles. In America, the expense of fitting up a 

 mile of telegraph is about £30, and being generally single wires, the 

 expense of maintaining them is inconsiderable. In this country the price 

 per mile is about £150, and the expense of maintenance proportionably 

 high. 



The plan invented by Mr. Mitchell, and which was illustrated by a 

 machine in working order, consists of only one wire. Instead of the 

 arbitrary and conventional symbols of the ordinary method, which are 

 deficient in precision, and liable to misapprehension, Mr. IMitchell employs 

 the ordinary Roman Alphabet and numerals, along with the common 

 figures. The letters are painted upon a segment in front of the operator, 

 and corresponding letters are inscribed on four- and- twenty ivory keys, 

 placed exactly as in the piano-forte, and touched in the same manner. 

 The letters are so distinct that a child could scarcely err either in com- 

 municating or receiving a message by the instrument. When one of the 

 keys is pressed down, a needle instantly points to the corresponding letter 

 on the segment ; and when a series of instruments are established at the 

 different stations along a line of railway, by the simple act of pressing 

 down the keys, one after another, the duplicate letters will be shown upon 

 all the instruments in the same circuit. From 80 to 100 letters can be 



