278 Proceedings of the British Association^ SfX. 



6. On a Copying Electric Telegraph; by Mr, F. C. Bakewell. 



In the method adopted for transmitting copies of writing, the letters 

 to be transmitted are written on tin-foil with varnish, so as to present a 

 conducting and a non-conducting surface. The foil is placed on the 

 cylinder of the transmitting instrument, and a metal style in connection 

 with a vohaic battery presses on the surface of the cylinder as it re- 

 volves. By this means the electric current is continually broken when 

 the style is resting on the varnish, and as the style is made to traverse 

 by an endless screw from one end of the cylinder to the other, it puvsses 

 necessarily over all the lines of the writing, and about eight times over 

 each line. 



The receiving instrument is similar to the transmitting one, and on 

 the cylinder of that instrument, paper moistened with a solution of | 



prussiate of potash in diluted muriatic acid is placed ; the metal style 

 on that instrument being a piece of steel wire. VVhen the electric cur- 

 rent from the positive pole of the voltaic battery passes through the 

 steel point to the paper, a blue mark is made by the production of 

 Prussian blue, — and when the cylinder is in motion, the effect is to 

 draw a series of spiral lines on the paper; but as the lines are broken 

 whenever the varnish writing on the transmitting cylinder interposes, 

 the forms of the letters are transferred from one instrument to the 

 other, — the writing appearing of a pale color on a ground of blue lines 

 drawn closely together. To produce this effect, it is requisite that 

 both instruments should rotate exactly together, and this synchronous 

 movement is attained by means of an electro-magnet, — one instrument 

 being made to regulate the other by retarding Its motion at regular 

 intervals. 



The regulation of the instrument is also facilitated by a guide-line, 

 consisting of a strip of paper placed at right angles to the writing, by 

 which means the person in charge of the receiving instrument can as- 

 certain how much the speeds of the two instruments differ, and by the 

 addition or subtraction of weight can bring the gaps formed by the 

 strip of paper to fall exactly under each other, — which indicates that 

 the two cylinders are revolving at the same rate. It was staled, in "^ 



answer to questions by members present, that two hundred letters per 

 minute might be copied by the Instruments exhibited, and that five hun- 

 dred in a minute arc attainable. To illustrate the facility which this 

 means of telegraphic communication affords for transmitting secret 

 messages, an apparently blank piece of paper was produced, on which 

 a message had been impressed invisibly before the meeting of the Sec- 

 tion, and by brushing it over with a solution of prussiate of potash the 

 writing became instantly legible. 



{To be continued.) 



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