March 10, 1882.] 



♦ KNO\VLEDGE 



401 



THE CRYSTAL PALACE ELECTRICAL 

 EXHIBITION. 



Fifth Notice. 



THE Exhibition may now be considered practically com- 

 plete. Marvellous progress has been made during 

 the last few days, and the Palace is crowded with visitors. 

 ^ van's exhibit is niagnilicent, but as it is our purpose to 



nsider next the various systems of incandescent lighting, 

 ..c refrain from making any further reference to it this 

 week. 



Telegraphy is well represented, the lead being naturally 



I ken by the British Postal Telegraph department. It is 



!iiewhat remarkable that this is the only branch of 

 .^'i'lied electricity in which any serious eflbrt is made to 

 exhibit a chain-like series of historic relics. The display, 

 however, lacks many interesting objects, in consequence of 

 the foreign Administrations not having loaned any of their 

 apparatus. 



The Post-office exhibits may be divided into two classes 

 — historic and modern. In the modern collection, interest 

 is chiefly centred in the Wheatstone Automatic Instru- 

 ment, by which messages may be transmitted at the rate 

 of 200 to 250 words per minute. It is used on circuits 

 which are required to carry a large amount of work, but 

 it is being gi-adually superseded on ordinarj- commercial 

 wires by duplex and quadruplex apparatus. Its applica- 

 bility to news work, that is, the transmission of long 

 messages for newspapers, is unequalled by any other form 

 of apparatus, and as this kind of work frequently amounts 

 to about 500,000 words forwarded from the Central Tele- 

 graph office during a single night, there is little prospect 

 of its Vicing relegated to the " historic " collection. 



Various other forms of telegraph apparatus are exhibited, 

 including duplex apparatus, by which messages may be trans- 

 mitted simultaneously in opposite directions ; but the quad- 

 ruple apparatus, by which four messages may be sent at a 

 time (two each way), is not exhibited by the Post-office. 

 The familiar single-needle instrument is shown, as well as 

 more the complicated fast-repeater apparatus, for both single 

 and duplex working. These latter sets are used where it is 

 drsired to increase the working capacity of long lines. 

 Practically, the repeater halves the length of the line. For 

 instance, suppose we have a wire from London to Glasgow, 

 and find that through certain causes, due to our uncertain 

 climate, we can only work at the rate of, say, sixty 

 words per minute. A station about mid-way, such as 

 Leeds, is asked to insert his repeater apparatus in the wire. 

 He does so, and, by an automatic arrangement, the current 

 which leaves, say, London, only goes to Leeds, where, by 

 moWngthe soft-iron armature of an electro-magnet, another 

 circuit is completed, and a current from the Leeds battery 

 goes on to Glasgow. 



The historic collection is very interesting, even to the 

 least curious of ^■isitors. It includes the oldest kno'mi 

 piece of telegraph apparatus, viz., Ronald's electric tele- 

 graph, which was laid as an experiment in Sir Francis 

 Ronald's garden at Hammersmith, in 1816. There are 

 also specimens of the Morse type, cast in 1832, when it 

 ■was supposed to be impossible for human fingers to mani- 

 pulate the apparatus in such a way as to be able to 

 distinguish between long and short signals. 



One of the most interesting objects is the " Fossil " 

 underground telegraph (1837). Fig. 1 is a diagram re- 

 presenting a section of this line ; it consisted of a kind of 

 triangular wooden rod, with five grooves, into each of 

 which a copper wire, covered with cotton and pitch 

 (tor insulating purposes), was laid. The grooves were 



then filled up by strips of wood. When thus finished, 

 it was laid underground. Such a line contrasts most 

 remai-kably with modem wires. It, however, serves 

 its purpose here, and takes the mind back really 

 a few years,'; but, apparently, many a century. The 



Fig. 1. 



line was laid in connection with Cooke and "Wheatstone's 

 five-needle telegraph, which was used at Paddington and 

 West Drayton in 1838. Fig. 2 represents the dial, or 

 reading portion, of the apparatus. There were five magnetic 

 needles, under the influence of as many coils of wire, each 

 coil being in a separate circuit, including one of the ■wires 

 represented in Fig. 1. The sending portion of the apparatus 



allowed of the current being sent from the galvanic battery 

 in either direction, so that each needle could be deflected 

 to the right or left. The letters of the alphabet (omitting 

 those which were deemed of least importance or necessity) 

 were marked on the dial as shoT\'n in the diagram. When 

 it was required to telegraph a letter, two needles were 

 deflected in such a way as to make both point to that 

 particular letter. In the diagram the letter " B " is thus 

 pointed out or telegraphed. 



In 1810 the five needles were reduced to four, but two 

 years later a most important change was effected. The 

 instrument only had two needles, and instead of their being 

 made to point out the letter, a code was arranged by which 

 movements of either or both needles to the right or left a 

 given number of times indicated the letter desired. 



Another interesting and important relic is Bain's 

 Chemical Telegraph (1850), in which the ordinary green 

 ribbon used in the Morse inker is replaced by wliite paper, 



