270 



UNDULATORY FORCES. ELECTRO-MAGNETISM. [DIA-XAONKTUH. 



each port The following are the storm signals wlontoc 

 by the Board of Trade. 



Fit . a. 



i 



No. 1. 



No. 5. 



No. . 



No. 4. 



NO.S. 



No, I. nmnnroni wind probably t rt from the wothwird. No. J 

 I>n B rruu wind prohibit- at flrt from the northward. No. 3. Dan- 

 frroiu win<! may be expccttd from nearly opposite quarttri uc- 

 ewlTelT. No. 4. Gait probably from the aoalhward. No. 5. Gait 

 probably from the northward. 



Wo will suppose, for instance, that the daily reports 

 from all parts of the kingdom have been received at the 

 usual hour of 9 A.M. A consultation is then hold as to the 

 chances of danger, and the probable direction of a storm 

 if one be likely to occur. Instructions are immediately 

 telegraphed to those ports nearly adjacent to the probable 

 locality of the expected tempest, to hang out the proper 

 signals, so as to warn vessels within sight of their im- 

 pending danger. In this way, at least, all that human 

 foresight and intelligence can do has been attended to ; 

 and the rest can only bo left to the discretion of the 

 captains, who have thus been forewarned. 



KLKTTKIO TIITK-BA.I.LS. Another valuable application 

 of telegraphs, has been that of indicating tho exact 

 moment when the sun has passed tho meridian of any 

 place ; or, what answers the same purpose, any exact 

 interval of time which has elapsed. It is usual to hoist 

 a large ball on the top of tho Observatory of Greenwich, 

 a little before one o'clock daily ; and at tho instant that 

 tho sun has passed one hour over the meridian (i.e., one 

 o'clock), tho time-ball is lowered. Tho captains of the 

 vessels in the Thames can thus daily check the rate of the 

 chronometers they have on board, and so gain the moat 

 valuable information ; because, on a correct knowledge 

 of time, depends their discovery of the longitude during 

 A long voyage. Within the last few years the system has 

 boon widely extended ; and by an arrangement of tele- 

 graphic signals between Greenwich, London (Charing- 

 cross), Liverpool, Glasgow, and other shipping ports, 

 the time-balls at each of those places are lowered syn- 

 chronously with that of Greenwich, and correct time is thus 

 indicated. The telegraph has also been employed for 

 ascertaining some interesting facts in connection with 

 astronomical science such as the longitude of two dif- 

 ferent places, etc. 



Modifications of telegraphic apparatus have been em- 

 ployed for domestic purposes; amongst which we may 

 notice the fire-alarum and house-bell. If wires bo con- 

 nected with the doors and windows of a house, and 

 arrangements be made so that, on any of these being 

 opened, contact shall be 'made between the wire pro- 

 ceeding from a small battery and an electro-magnetic bell, 

 inch may be readily applied for tho purpose of warning 

 the inhabitants of the ingress of persons ; and as a pro- 

 tection against thieves. By means of a most ingenious 

 arrangement of a thermometer and eloctro-magnot, a 

 fire-alarum has been constructed. Tho thermometer is 

 of peculiar construction; and tho nvrcury it contains, 

 is, in ordinary circumstances, at some distance from a 

 little arm, which can connect an electro-magnet with an 

 alarum-bell. If, however, the temperature of the room 

 rapidly and greatly increase, then the expansion of the 

 mercury in the thermometer raises tho arm, and com- 

 pletes the connection between tho battery and tho olec- 

 tro-magnet of the alarum ; and on this taking place, a 

 detent is removed, and the bell at once commence! to 

 sound, and so give* the alarm to tho inmates. 



With this, we must now draw our observation! and 

 experiments, in connection with electro-telegraphy, to a 

 conclusion. We have attempted to put our readers in 

 posMmion of the leading fact* of the subject; but 



have been compelled to omit many interesting particulars. 

 It is impossible to regard the discovery of this mode of 

 communication otherwise than as tho greatest that has 

 been made in this century, if all point* are viewed. 

 It has but one rival photography; but that rivalry is 

 more in the nature, rather than in tho extent and value, 

 of its applications. We may, for * moment, take a 

 hasty glance at the advantages which accrue to residents 

 in large towns ; and, for example, we shall confine our 

 attention to London, and its telegraphic connections. 

 For a few pence, we can communicate our wishes to any 

 part of tho metropolis, and receive an instantaneous 

 reply ; the amenities of friendship, and the necessities of 

 the household, can be simultaneously attended to, and 

 communicated, over our housetops ; and a conversation 

 can easily be held between two friends, at any distance 

 from each other, whilst both may be within their houses, 

 if advantage bo taken of the arrangements made by one 

 of the telegraphic companies. The professional man can 

 be called to the sick chamber at a moment's notice, or the 

 relations and family friends suddenly summoned from all 

 parts of the metropolis, to take a last farewell of a beloved 

 one. Tho man of business has scarcely to conceive a 

 new scheme, than all the arrangements necessary for its 

 success can, in a few minutes, be made by communicating 

 through the telegraph, to his agents in any part of Europe. 

 Does he desire to receive even an amount of money, this 

 the telegraph will send him. If he be anxious to change 

 the intended destination of a vessel, to take advantage 

 in a change of markets, this the telegraph can effect for 

 him. A man can now as readily converse with his re- 

 presentatives in St. Petersburg, Vienna, Constantinople, 

 Berlin, Madrid, and Paris, as he can with his neighbour 

 in the next house to him. The politician can summon 

 his adherents simultaneously from all parts of the king- 

 dom and the continent, in cases of important divisions 

 in the Houses of Parliament. The diplomatist may con- 

 verso with his antagonist, and, at the same moment, 

 receive instructions from his government, hundreds of 

 miles away. Armies and navies, at the most distant 

 places, can be commanded by the home authorities with 

 as much readiness as by their commander on the spot ; 

 and, as we have lately seen, the two potentates of tho 

 two greatest nations on the earth her Majesty the 

 Queen, and the President of the United States were 

 enabled, by means of a slender wire stretched under 

 3,000 miles of the stormy ocean, to speak words of peace 

 and good-will, as the representatives of two nations, 

 using the same language, having brotherly ties, ami 

 divided, not in sentiment, but by position only. \\V 

 may almost imagine that the triumphs of science can 

 proceed no further. But we cannot forget that tho 

 realm of nature is boundless ; and, despite all <>ur 

 successes and achievements, we have but entered tho 

 threshold of that storehouse in which are yet buried, but 

 only to bo discovered, wonders and truths, which, when 

 brought to light, shall eclipse all our past discoveries. 



DIA-MAGNETISM. 



WE shall now make a fow remarks on an interesting 

 jranch of physical science, for which we are indebted to 

 ;ho researches of Dr. Faraday. In tho early port of 

 liis work, we called frequent attention to tho fact, that 



each of the undulatory forces had a distinct relation and 

 :onncction with the rest ; and tho last link in this sin- 

 gular chain, is supplied by tho facts of dia-magnctic phe- 

 loinena. We shall And that oven a ray of light may bo 

 lubjocted to magnetic influence ; and thus our ideas of 

 Magnetism, and the objects to which it has affinity, will 

 '< much enlarged. 



We have already explained, that a ray of polarised 

 ight lias properties highly different to those found in 



common light. It will not obey the same laws ; and 

 > resents, under certain circumstances, some very peculiar 

 ihenomona.* 

 If a ray of polarised light be sent through a mass of 



heavy glass which, for this purpose, is made of borate 

 See ante, p. 80. 



