JJ3S 



THE POPULAR EDUCATOR. 



N is the separate condenser into which cold water is injected 

 from the cistern around, the amount being regulated by the 

 cock moved by the handle seen above it. This water and the 

 air it contains would, however, soon accumulate and stop the 

 action of the condenser ; a valve is therefore placed at the 

 bottom opening outwards, and a pump, moved by the rod E, 

 removes the water through this at each stroke. This water is, 

 of course, -warmed by the condensed steam, and is therefore 

 usually employed to feed the boiler. 



Another rod, F, on the end of the beam carries on it two small 

 tappets, a and b; these give motion to the valves which regulate 

 the steam. There are three of these m, n, and o, all of which 

 are placed on one vertical rod ; m and o open upwards, while n 

 opens downwards. The rod which carries them is attached to 

 one end of the bent lever k c d, the other end of which terminates 

 in an eye or fork, through which the tappet-rod marked F in 

 our illustration moves. 



To understand the action, let us suppose the steam to be 

 turned on, the valves being in the position shown. It will then 

 pass from the boiler through the steam-valve m, and thus press 

 on the upper surface of the piston. The space under this, being 

 in connection with the condenser through the eduction-valve 

 o, is a vacuum, and there is thus no resistance offered to the 

 downward movement of the piston. It accordingly sinks, and 

 in so doing raises the counterpoise, Q, and the pump-rods. 



The rod F falls at the same time, and just before P reaches 

 the bottom, the tappet b catches the bent lever, and lowers the 

 valve-rod ; m and n are thus at once closed, so that the cylinder 

 is shut off from the boiler and from the condenser too. The 

 equilibrium valve n is, however, opened at the same time, and 

 thus makes a communication between the upper and lower ends 

 of the cylinder, so that the pressure on each side of the piston 

 becomes the same. The counterpoise Q accordingly lowers its 

 end of the beam, and thus raises the piston to the top of the 

 cylinder. 



In doing this the lower tappet raises the lever again, so that 

 the equilibrium valve is closed. The lower end is then, as at 

 first, in communication with the condenser, and the steam in it 

 is condensed, while the pressure of the steam on the piston 

 again depresses it, and in this way the motion is continued. 



Another great improvement effected by Watt was that of 

 working the steam expansively. An example will make this 

 quite clear. Let the cylinder be 6 feet long, and have an area of 

 40 square inches, and let the steam press on it with a force of 

 25 Ibs. per square inch. The total pressure on the piston will 

 then manifestly be 1,000 Ibs. ; and to drive the piston along the 

 cylinder with this pressure will require a given amount of 

 steam. Now let us suppose the steam-valve closed when half 

 the stroke has been performed. Only half the amount of steam 

 will be used ; the piston will, however, still continue to be 

 forced down by the expansive power of the steam, but the 

 force gradually diminishes till, when the piston reaches the 

 bottom, the steam has expanded to twice its original bulk, and 

 therefore exerts only half the pressure viz., 12,^ Ibs. per square 

 inch, or 500 Ibs. in all. We can easily calculate the mean 

 pressure during the latter half of the stroke, and shall find it to 

 be a little over 700 Ibs. We have, therefore, the piston forced 

 through a space of 3 feet with the force of 700 Ibs. without any 

 further amount of steam. The amount of work accomplished by 

 the same expenditure of fuel is in this way increased 1*7 times. 

 Ey cutting off the steam at an earlier portion of the stroke, a 

 much greater increase of power is attained, and many engines 

 are now made which are worked with steam at a very high 

 pressure, the valves being closed at one-eighth or one-twelfth 

 of the stroke. This is easily effected by a suitable arrangement 

 of the tappets. 



LESSONS IN GREEK. LII. 



MOODS. 



THE moods represent the circumstances under which the subject 

 is united with the verb, or the manner in which the affirmation 

 of the verb is made. In simple propositions the indicative, the 

 subjunctive, and the optative moods are employed ; the im- 

 perative is a form by itself, since the imperative does not make 

 a simple statement. 



The office of the indicative mood is merely to indicate or 

 declare a reality. In Greek the use of the indicative generally 



resembles its use in other languages. Some peculiarities, how- 

 ever, have to be set forth. 



The indicative, in union with the particle av (ict, Kev), pre- 

 sents a condition whose realisation depends on circumstances, 

 to which reference is made by the conjunction. This form of 

 speech occurs partly in the historical tenses and partly in the 

 future. 



The indicative of the historical tenses, in connection with oi/, 

 denotes that a condition takes place as often as the requisite 

 circumstances occur, consequently neither always nor merely 

 once ; as, for example, on fj.a9otf^' fKaffrore, fire\av6avofj.riv av 

 v6vs, whatever on each occasion I learned, forthwith I commonly 

 forgot it. 



The force of the idiom may be illustrated by the use of our 

 conditional would, denoting repetition under certain alleged 

 circumstances : 



" These things to hear 

 Would Desdeuioua seriously incline." 



The indicative with av also signifies that a condition has not 

 taken place or cannot take place, since the requisite circum- 

 stances do not exist ; as, T(S ai> tfr/dri rav-ra ^-systrOcu ; who could 

 believe that these things happened ? 



Frequently are these forms used etSes av, you would have 

 seen ; r)yr)ff(a av, you would have thought ; eyvw av ris, one would 

 observe. 



Sometimes for the expression of this sense you find the indi- 

 cative without av, when the condition which under certain cir- 

 cumstances would have taken place is represented as actually 

 taking place ; as, jjicr^ui/o^uTjr yuerroi, ei viro TroAe.utot; t^iraTi]Qi\v, 

 I should be ashamed indeed if I were deceived by an enemy. 



So wishes which are not fulfilled and cannot be fulfilled, take 

 the indicative without uv; as, w^eAe Kvpos &)y, would Cyrus 

 were alive. 



The indicative of the future in union with av (in the poets /ce, 

 Kff) signifies that a future event is not absolutely certain, yet 

 is in a high degree probable ; and this construction is more fre- 

 quently found in Homer : for example, ey<a 5e KC TOI Sucrus, / 

 will give it thee, if I can. 



Suppositions are sometimes uttered as facts. This is done 

 by the employment, in the indicative, of an independent sen- 

 tence, instead of a foregoing hypothetical one. This form of 

 speech is used partly when a supposition is put in a general 

 and unconditional manner ; partly when the speaker intends to 

 take to himself an unfounded statement of another ; for which 

 we employ the preparatory words suppose that, granted that ; 

 as, aoiKei ris fKtav opyi) KO.I riwapta KT' avrov, some one ad- 

 visedly does wrong (i.e., we will suppose that, etc.) ; there arc 

 anger and punishment for him. 



The subjunctive and the optative moods denote that the 

 predicate is applied to the subject according to a conception ; 

 and the relation between the two is one of dependence, which 

 may exist exclusively in the mind, or it may exist in the mind 

 as represented by a verb or a conjunction. 



Homer, and the epic poets in general, put positive as well 

 as negative propositions sometimes in the subjunctive. By 

 this mode of expression it is intimated that the speaker has not 

 a certain but only a doubtful idea of the matter in question ; 

 and consequently the form serves to set forth an opinion, or an 

 undecided notion ; as, KO.I irore rts tiirri<nv, and once, I suppose, 

 some one said. 



The occurrence in a simple sentence of the subjunctive with 

 ov fji.7i and JUTJ ov is only apparently irregular, since the expres- 

 sions are elliptical, something being understood ; so that in the 

 full exhibition of the proposition the subjunctive would appear 

 as a subordinate sentence. The words <po/3os ttrrt (there is a 

 fear), Seos ttrri (it is a duty), are to be supplied with ov /IT?: for 

 example, the sentence ov /UTJ ae cnroAtTrai would read in full, ov 

 <f>o&os effTt jitTj tre awo\nro>, there is no fear that I should leave 

 thee. 



In sentences with /XTJ on we must understand or supply before 

 the (J.TJ 6pa, see, or <ntovti, consider. The phrase, therefore, 

 serves to express an undecided or doubtful denial ; as, aAAa /J.TJ 

 OVK fj ditianTov apery, but virtue can scarcely be taught. 



The optative, which represents a conception as lying to the 



speaker beyond the present, finds its propar application in the 



expression of a wish. Of the use of the optative in simple 



propositions there are two different forms, namely, the simple 



| optative and the optative with- av. The optative without av 



