162 



THE POPULAR EDUCATOR, 



covered when the jug is full of carbonic acid ; and as this gas is 

 half as heavy again as common air, it may be poured from the 

 jug into the deep ale-glass in which the pill-box and gun-cotton 

 have already been placed : by this simple arrangement the trouble 

 of perforating a cork, and fitting it with a bent tube to a bottle 

 containing the materials for generating carbonic acid, is saved. 



The current of burnt gas and heated air that escapes from 

 the top of an argand burner is usually very hot, but does 

 not evolve light, as it is estimated that a current of gaseous 

 matter may have a temperature of 2,000, and yet not become 

 luminous. 



If, however, a spiral of fine iron or platinum wire, or a bit 

 of asbestos, is held in the hottest part of the current of air, 

 ignition of the solid thus employed takes place, and light is 

 evolved. The increase of heat in the solid is seen better 

 when the glass chimney of the argand burner is covered with 

 tin-foil to within two or three inches of the top, as the glare 

 from the lamp frequently overpowers the light from the in- 

 candescent wire. 



In all cases where artificial light is obtained, the ignition or 

 incandescence of some kind of solid matter takes place ; with 

 gas or oil it is the carbon. The oxy-hydrogen or lime light is 

 a remarkable illustration of the same fact, the mixed gases, 

 oxygen and hydrogen, hardly giving out any light when burnt 

 alone ; but if directed on to a piece of lime, the latter becomes 

 gradually so hot that it emits the most dazzling rays of light. 

 Even the electric light as first known to us, which may be con- 

 sidered the most intense and brilliant of all artificial lights, is 

 produced by the ignition of two points of charcoal, through 

 which the current of electricity from a powerful battery is passed. 

 The ignition of the carbon is wholly independent of the air ; no 

 combustion is necessary. A transfer of solid particles of charcoa 

 takes place from one pole to the other, which goes on quite as 

 well, if not better, in the vacuum of an air-pump. 



Directly after the ball of lime has been used for the produc- 

 tion of the oxy-hydrogen light it sometimes continues to emit 

 a very faint light. This is due to phosphorescence, another 

 and most curious source of light. Phosphorescence occurs 

 with certain living organisms ; there are luminous animalculao 

 in the ocean, luminous insects, such as the fire-fly, and a lumi- 

 nous worm, called the glow-worm, from which Matteucci ex- 

 tracted a yellowish phosphorescent substance. The decay of 

 organic matter is usually the result of an oxidising process, but 

 the phosphorescence of certain fish, such as whitings and her- 

 rings, does not appear to be due to oxidation, because the light 

 is not reduced when the fish is placed in nitrogen or hydrogen. 

 At the moment of crystallisation, flashes of faint light are some- 

 times seen, and especially when the saline substance, such as 

 sulphate of soda, has been fused at a red heat, cooled, dissolved 

 in water, and crystallised. Fusion or vitrefaction, followed by 

 subsequent solution in water, and crystallisation appears to be 

 accompanied most frequently with these appearances of light. 

 A brass button fitted on a cork, and rubbed violently against a 

 small piece of wood, soon affords enough heat to set fire to a 

 piece of phosphorus. The attrition of a flint against a hard 

 metal, such as steel, is said to " strike fire ; " and in this case 

 friction becomes a direct source of light. On the Underground 

 Eailway sparks of fire generally accompany the application of 

 the brake, as the train is brought to a standstill at the various 

 stations. The sparks from the wheels, or the flint and steel, are 

 derived from minute particles of metal which are rubbed off by 

 friction, and being very hot burn in the air. 



When electricity of high intensity lightning darts through 

 the air in the discharging of electrified clouds, the flash of light 

 is most overpowering, and in some cases has caused blindness. 

 The nearest imitation of Jove's lightnings is that obtainable 

 from a great inductorium coil and some Leyden jars : the noise 

 of the discharge, the intensity of the light, its peculiar colour, the 

 rapidity with which it comes and goes, remind one of Juliet's 

 pretty speech : 



" I have no joy of this contract to-night : 

 It is too rash, too unadvised, too sudden; 

 Too like the lightning, which doth cease to be, 

 Ere one can say ' It lightens.' " 



All terrestrial modes of obtaining light, such as friction, che- 

 mical action, ignition of solids, phosphorescence, crystallisation, 

 and electricity, sink into insignificance before the great natural 



source of light, the sun, the centre of our planetary system, and 

 the great source of heat and light to the world. 



Sir John Herschel has estimated that " the sun gives out as 

 much light as 146 lime-lights would do, if each ball of lime 

 were as large as the sun, and gave out light from all parts ot its 

 surface;" and that "the heat evolved from every square yard of 

 the sun's surface is as great as that which would be pfoduced by 

 burning six tons of coal on it each hour." 



The heat and the light of the sun come from an envelope, 

 called the photosphere, and this is supposed by eminent a.stro- 

 nomers to be neither solid or liquid, but cloud-like and gaseous ; 

 of this they are almost certain, although the actual source of 

 the heat and light of the sun is unknown. 



READINGS IN GREEK. III. 



DEMOSTHENES. 



OP all the brilliant array of orators that Greece produced, 

 Demosthenes has always enjoyed the highest reputation. Living 

 as ho did at a critical and eventually disastrous period of the 

 history of Athens, he took an active interest from a compara- 

 tively early age in political affairs, and throughout his life was 

 constant in his endeavours to stir up and keep alive the fire of 

 patriotism and courage which had well nigh become extinct in 

 the bosoms of his countrymen. The whole of Greece was 

 gradually falling under the sway of Philip of Macedon, whose 

 schemes of aggrandisement were afterwards carried out so 

 extensively by his son, Alexander the Great ; and it was chiefly 

 against the policy of the Macedonian king that the efforts of 

 Demosthenes were directed. But bribery and craft soon did 

 their work ; the Athenians offered but a half-hearted resistance 

 to the invader, and the year B.C. 338 witnessed the downfall of 

 the liberties of Greece at the disastrous battle of Chaeronea. 

 The news of the defeat filled the Athenians with the utmost 

 consternation, and at this terrible crisis, Demosthenes, in whom 

 the people placed unbounded confidence, exerted all his energies 

 for the defence of Athens. The crisis passed, owing in a great 

 measure to the prudent forbearance of Philip partly, also, no 

 doubt, to the energetic exertions of Demosthenes ; and some 

 seven months later an Athenian citizen named Ktesiphon got a 

 decree passed that a gold crown should be given to Demosthenes 

 in recognition of his services to the state. For this action Ktesi- 

 phon was impeached by the Macedonian party in Athens, and 

 the indictment was entrusted to J3schines, the rival and deter- 

 mined opponent of Demosthenes. Though directed nominally 

 against Ktesiphon, the prosecution was, in fact, an impeachment 

 of the whole political career of Demosthenes, and .ffischines 

 endeavoured to prove that his rival's policy was not only 

 undeserving of commendation, but even positively censurable. 

 The reply of Demosthenes is contained in the magnificent ora- 

 tion " De Corona " (On the Crown), in which the great orator 

 unflinchingly accepts the challenge held out to him, and shows 

 triumphantly that ^Eschines and his party were the real traitors 

 to their country and the abettors of her ruin. The first extract 

 is taken from an early portion of the speech : 



DEMOSTHENES. "Ds CORONA," 12,13. 

 Ta /j^v ovv KU.TrryopritJ.fva 1 tro\\d, Kal Trepl 5*< 2 ev'uav f*.tyd\as 

 Kal ras tffxdras ol v6p.oi SiSoaffi rt/j.u>plas- TOV tie irapovTOS aycavos 

 fi irpoaipeffis* avTrj- ex^pov fit? tirriptiav* x t Ka ^ v&P LV al \oi- 

 Sopiay teal jrpoirrjAaKJCTjubj' dpov Kal iravra TO. rotavra, riav /j.fvrot 

 KaTijyopicav Kal ro>y alriiav Ttav flprjfJLfvtai', ft irtp fyffav a\ridf'is, 

 OVK tvi & rfj TrJXet StKTjv aiaj/ Aa/Hel*/, ovS' eyyvs' ovyap f a<J>aipei'cr0at 

 Se? TO irpofft\6f'tv j -rip S^py Kal \6yov rvxtu', ov8' Iv iirf\pt(a.s 

 Tafej 8 Kal <t>06vov rovro Ttoifiv oij-re p.a rovs Ofous o>. leas fX" ^ Tf 

 iroKniKbv ofcf Si'/caioV ecrriv <t> avSpfs 'Aflrji/cuor a\\' ecp' oTs 

 aSiKovi/To. /j.f fiapa trjV ir6\iv, oZffl ye TTI\IKOVTOIS fa'iKa vvv trpa- 

 yfSft 9 Kal 8<ej7ei, rals <=/c ruiv v6fj.cav ri/j.(apiais trap' avra Ta5i/c^- 

 /iara 10 xP^ ff ^ a '> n e * M* y ficrayyf\ias 12 &|ia Trpdrrovrd /ue etiipa, 

 (laayyt\\ovTa Kal rovrov TOV rpovov els Kpicriv KaBiaravra. trap 

 vu'tv, (I Si ypdfpovra irapdi'O/j.a, irapav6fji(av ypa<po/j.(vov. 



NOTES. 



1. KaTFjT., the counts of iJie indictment ore many. Supply erfri. 



2. Kai irepi wv. A contracted form of expression for Toiaura or <='nei*. 

 pi iav. And of such a nature that far some rflUem. 



3. itpoaiptcrit means originally deliberate choice, and thus infanttonv 

 This is the intention o/ the present suit. 



