106 



THE POPULAR EDUCATOR. 



hydrogen, and combining with the oxygen to form an oxide of 

 zinc. The hydrogen, however, instead of rising as a gas, de- 

 composes the particle of water next to it, uniting with its 

 oxygen to re-form water. In the same way the hydrogen thus 

 set free unites with the next particle of water, and thus the 

 copper plate is at last reached, where the hydrogen rises in the 

 form of a gas. 



The oxide of zinc formed is at once dissolved by the acid, and 

 thus a clear surface of the zinc is left to bo immediately again 

 oxidised. The electricity is, however, produced by the decom- 

 position of the water, and not by the solution of the oxide of 

 zinc. This, then, is our simplest form of galvanic battery, and 

 by it a considerable quantity of electricity may be obtained, 

 though of very low intensity that is, it cannot pass along if 

 any great resistance be offered, and appears to have but little 

 power of penetrating any substance. 



If the plates have an area of ten or twelve square inches each, 

 and a piece of fine platinum wire about half an inch long be 

 placed between the ends of the wires connected to them, the 

 electricity will, in its passage, render it red-hot. 



In a battery of this kind, the quantity of fluid generated 

 depends upon the size of the plates. When, therefore, large 

 quantities are wanted with but little tension as, for example, 

 in exhibiting the heating effects of the current one with large 

 plates is employed. 



The largest ever made was one constructed under the direc- 

 tion of Mr. Pepys for the London Institution. It consisted of a 

 sheet of copper and one of zinc, each measuring fifty feet in 

 length by two feet in width. These were wound round in a 

 spiral form, horse-hair ropes being placed between them to 

 prevent their touching, and the whole could be lowered into a 

 large vessel which held about fifty gallons of dilute acid. The 

 quantity of electricity obtained from these was immensely 

 great, calorific and chemical effects being manifested in a most 

 marked way. 



By more recent modifications, however, batteries are con- 

 structed containing two liquids, which have more power than 

 large ones like that we have been speaking of. 



There is one point which it is very important for us clearly to 

 understand before proceeding further, and that is the direction 

 in which the current passes. In the battery we have been ex- 

 plaining (Fig. 5) the zinc is the positive metal, which we remem- 

 ber by thinking that it is the one which is positively acted on ; 

 the copper, therefore, is negative. As, however, the current 

 passes from the zinc to the copper in the liquid, it will be seen 

 that the pole or electrode attached to the copper plate is the 

 positive one, while that attached to the zinc is the negative. 

 In other words, the + electrode is attached to the - plate, 

 and the - electrode to the -f- plate. This is at first rather 

 confusing, but a little thought will make it clear ; and the 

 following aid to the memory may be of use in recollecting 

 which pole is -J- and which - ; the p in copper may be taken 

 for positive, and the n in zinc for negative. The direction may 

 be further fixed upon the mind by remembering that the current 

 passes from Z in the liquid to C, and Z in C forms the word 

 zinc. This may appear an unnecessary explanation, but the 

 advantage of having it well impressed upon the mind will be 

 evident to the practical student before he has proceeded far in 

 his study of the science. We must defer till our next lesson 

 the notice of the different kinds of battery in use. 



LESSONS IN GREEK. XXXVI. 



CONTRACTED PURE VEKBS (continued). 



CONTRACTED VEBBS WHICH, CONTRARY TO THE RULE, RETAIN 

 THE SHORT VOWEL. 



As in some uncontracted pure verbs, so in some contracted 

 pure verbs, the short characteristic vowel of the root remains 

 In the derived tenses. Most of these irregular verbs take cr in 

 the perfect middle or passive and in the first aorist passive, 

 as well as in the tenses thence formed. This fact is indicated by 

 the form " pass, with a-." They are the following : 



1. aco. 



FeAaci), J laugh, fut. yf\a.(rofj.ai, aor. fyt\affa ; pass, with a. 

 EAaco (commonly eXavpca), I drive, fut. (\affta (Attic e\u), aor. 



TjAdcra. 

 0Aaco, I squeeze, fut. 0Acurco, etc.; pass, with ff. 



KAcwo, I break, fut. K\a<ra>, etc. ; pass, with ff. 

 XaAioi, I relax, unbind, fut. x a ^ affca > e ^ c - > P a ss. with a: 

 AO./J.OW (commonly 5a/uao>), T tame (Lat. dome), aor. f$a/na.ffa.. 

 llepc.o>, I carry over, fut. ir^io.ffca, aor. eirepUffa ; but Trepan, I go 



over (intrans.), fut. irepaffta, aor. eirepaffa. 



2irau>, I draw asunder (spasm), fut. cnracrco, etc.; pass, with IT. 

 2x<<>, I loosen, open, fut. ffxaffta, etc. 



2. a>. 



Ai5eofj.ai, I reverence, fut. ouoWoyUcu, aor. 7j8e(T0r;p , perf . ySeffpcu. 

 AKtofnai, I heal, fut. a.Kfffo/j,ai, aor. mid. i\K.fffa.jj.Tjv, perf. Tj/cetrjuat. 

 AAeto, I grind, fut. a/\ecrai (seldom a\ta), perf. mid. or pass. aArj- 



\fff/J.at. 



ApKt<a, I suffice, fut. apKtffta, etc. ; pass, with tr. 



E/ueco, I vomit, fut. e/ueo-o), etc., perf. act. e/xr/^e/ca, perf. mid. or 



pass. e/xTj/uecrjucu. 



Zew, I seethe, boil (intrans.) ; pass, with a. 

 eifca, I scrape; pass, with ff. 

 TfAew, I end, fut. reAa> ; pass, with ff. 

 Tpeco, J tremble, fut. rptffia, etc. Verbal adj. Tpe-<r-Tos. 

 Xea>, I pour ; Attic x e&) > X e(S ' X 6 ' > aor - 1 6 X a > perf- Kex^Ka, 



perf. pass. Kexv/J-ai, aor. fx^drji' . 



3. oco. 



Apoca, I plough, fut. apoffw, aor. rjpocra, perf. mid. or pass, aprjpo* 

 fna,i, aor. pass. rjpoBijv. 



The following in some tenses have the long vowel, in others 

 the short one : 



Eiraipfco, I praise, fut. firaiveffo/j.ai, aor. eirr/j/etra, perf. eTrpvsKa., 

 aor. pass. tirriffBriv, but perf. mid. or pass. (Trjivr)/j.ai. 



i/jew, I take, aor. pass. ypfOrjv ; otherwise rj, aa oiprjcra), rjpr)i<a, 



Afu, I bind, Srjffcii, fS-rjffa, eSrjffa/j.rjv, but SeSfiea, SeSe/uat, fSeOyv ; 



fut. pass. Sedrjffo/j.ai, for which the third future, 5et>T)ffo/j.cu, 



ia commonly used. 



KaAf ta, I call, fut. /coAeo, aor. etcaXfffa, but perf. Ke/cArjKct, etc. 

 Tlodeca, I long for, TroBr/ffca, Troflr/ero/xai, firod-tjffa, and (iroOfffa, 



irtiroOrjKa, irfiroQ-qfuai, eTroflecrSijc. 

 riovtca (Lat. labaro), I labour, work, trovrjaw ; but iroveffta, I shall 



be in pain ; irfirov^Ka, in both meanings ; mid. iroveiffQat, to 



be fatigued, fut. irovriffofna.1., etc. 



MODELS. ACTIVE. 



Tenses. Characteristic a. Characteristic e. Cliaractaristic o. 



Pres. 2ir(aa>)A>, J draw Te\(e-a>)a>, I end. Ap(o-w)ia, 1 'plough. 



apart. 



Imperf. fffir(a-oy)cai/. eTf\(f-ov)ovv. T)p(o-ov)ovv. 



Fut. ffiraffcii. TeAai. uporrca. 



Aor. iffiraca. ere\f(ra. rjpoffa. 



Perf. fffiraica. TereAe/ca. op-Tjpo/ca. 



Plup. effiraKeiv. eTereAejceip. ap-ijpoKfiv. 



MIDDLE. 



Pres. ffTr(a-o)ca-fj.at. TA(e-o)ou-;ucu. ap(o-o)ov-fj.at. 



Imper. tffir(a.-vi)<a-^.Tiv. tTf\(e-o)ou-jji7]i>. tjp(o-o)ov-fj.riv . 



Fut. ffira.ffofj.iu. Te\ou/j.ai. apoffofj.a.1. 



Aor. ecr7ra-<ra-jU7jj'. ereAecra^^i'. i\poao.fi.i\v. 



Perf. efriro-a-juai. rfre\eff/j.ai. ap-rjponai. 



Plup. (ffira.-ff-ft.-nv. ereTf:\ffffj.r]v. ap-7]po/j.i]v. 



PASSIVE. 



Aor. fffiraffBrjv. Tf\fff6r]i>. ijpoOriv. 



Fut. <r7ratrflr/o"0juat. rf\fff6r)ffo^ai. a,po9r)ffO[iai. 



Verbal Adjectives : ffiraffreos. re\effTfos. aportos. 



The further flexions of tfftra.ffft.ai, etriraffyUTjj', Tfrektfffj.ai, ere- 

 Tf\ffffJLtjv, are like KfKt\<=v<Tfj.a.t, e/ce/ceAeixrjur/r, already spoken of. 



The following contracted verbs take ff in the passive, though 

 they lengthen the characteristic vowel in the tenses ; namely 

 Neoi, J spin, vfvrifffna.1 and vevrj/nai, but wrjOnv. 

 Na>, I heap up, vtvT}fff.ia.i and vfV7]fj.at, but wr\<rQ-r\v. 

 Tl\tca, I sail, ir\vcrou.ai, eirKtnffa, Trar\fvKa, ireir\fvfffj.ai, eTrAet/tr- 



*pea>, only in compounds, as eK(pptca, I cam/ out, 

 Xoco, J accumulate, x"><ni>- 

 Xpaw, I give an oracular response, xP'7 <ra / a7 /''- 

 Xp3.ofj.ai, I use, has in the perfect middle KfxPW' I have used,, 

 but in the aorist passive expriff6riy, I was used. 



On the contrary, eAaoj, aiceco, alpeco, Sea>, and apoca, do not take 

 the ff, though the characteristic vowel in the perfect middle or 

 passive and in the aorist passive remains short. 



