66 



T3E POPULAR EDUCATOR. 



Fig. 71 represents the general construction of a bar magnet. 

 The ends of the wire are in this twisted together, and binding- 

 ecrews attached to them to join the battery wires to. 



Sometimes, instead of the wire being wound directly on the 

 core, a large reel is procured, the tube of which is made of paste- 

 board or thin wood, and the wire is coiled on this. The core 

 may then be inserted in the reel, and changed at pleasure ; the 

 distance to which it projects may also be altered if desired. 

 Bars of other metals may likewise be inserted in the reel, so as 

 to observe the effect, if any, produced on them by the passage 

 of the current. By the employment of a series of such reels, 

 wound with different lengths and sizes of wire, the various 

 effects thus produced may be investigated. 



Not only does a magnet attract pieces of iron held near its 

 poles, but it converts them into magnets, so that they in turn 

 will attract others, and thus a chain of pieces of iron may be 

 suspended, as shown in Fig. 72. In the figure, however, a 

 permanent, and not an electro magnet is represented, but the 

 same result is obtained whichever is employed. 



A beautiful illustration of this is seen by throwing a number 

 of nails on to the ends of the electro-magnet, and then scatter- 

 ing iron filings over them. Many of the nails will stand on 

 end like branches of trees, while the filings cluster round them 

 so as to resemble foliage. As soon as the contact with the 

 battery ceases, all at once drop, but spring up again on renew- 

 ing it. 



The magnetic power will penetrate many substances. Let a 

 plate, for instance, be placed over the magnet, and iron filings 

 sifted on it ; they will at once collect opposite to the poles of 

 the magnet, and shift their places as the plate is moved about. 

 The filings, too, will arrange themselves in curves, indicating 

 the lines of magnetic force. 



Advantage is sometimes taken of the attractive power of the 

 magnet to separate iron and brass filings. The poles are dipped 

 into the mixture, and the magnet is gently tapped, so as to 

 remove all particles of brass accidentally entangled with the 

 iron. It is then moved over a tray to receive the filings, and 

 contact with the battery broken, when they at once fall. 



The horse-shoe form is employed more frequently than the 

 straight bar. Fig. 73 shows the mode of making a magnet of 

 this kind. A piece of iron rod is bent in the middle so that the 

 sides may be parallel, and its ends are then filed true. The 

 wire is wound along one limb nearly to the bend, and then 

 carried across to the other. It may be wound round the curve, 

 but it is usually found more convenient to leave that bare. 

 The wire must, however, be wound in the same direction on 

 each limb, as will be seen in the figure, where, after leaving the 

 upper side of the left-hand limb, it passes to the under side of 

 the right-hand one. Only one layer is here shown ; in practice, 

 however, several are laid one over the other, or else reels are 

 placed on each limb. 



The keeper, A (Fig. 73), is a bar of iron made to fit evenly to 

 the poles, and a hook is usually fixed to it, that weights may be 

 suspended from it. 



To avoid the resistance caused when the current has to tra- 

 verse a great length of wire, three or four separate lengths are 

 sometimes wound on, the ends being united into bundles, and then 

 connected with the battery. Care must be taken in this case 

 that the current travels in the same direction round each coil, 

 as otherwise they will to a great extent neutralise one another. 



Magnets of this kind have been constructed of very great 

 power, capable of lifting from 10 to 20 cwt. when a powerful 

 battery is employed. For testing the weight that can thus be 

 sustained, the magnet is usually suspended from a strong stand 

 (Fig. 74), so arranged that the keeper may rest on two sup- 

 ports a little lower than the poles. A large pan or board is 

 then suspended from the hook of the keeper, and to this 

 weights are added till the attraction of the magnet is overcome. 

 Sometimes a second magnet is inverted under the first, and 

 so arranged that the same current may pass round the coils 

 of both ; the north pole of the one is then placed opposite to 

 the south pole of the other, and in this way a great increase of 

 power is gained. 



By means of a powerful electro-magnet, it is very easy to 

 make any number of permanent magnets. Take a bar of steel, 

 and placing its middle point on one pole, draw it slowly off it 

 two or three times ; now repeat the same process with the other 

 end of the bar on the other pole, taking great care always to 



draw it from the middle to the ends ; after repeating this a few 

 times the bar will be found to be converted into a powerful 

 permanent magnet. 



It is not even necessary for the steel to touch the magnet, as 

 a faint polarity may be imparted to it by being held near to it. 

 We had once an unpleasant illustration of this, when, after 

 trying various experiments with a powerful magnet, we found 

 that the balance-wheel of our watch had become so magnetised 

 that it had to be replaced by a new one. Since then, whenever 

 experimenting with magnets, watches have been carefully laid 

 aside, and we advise the student always to do the same. 



In a similar way, if a magnetic needle be held near a power- 

 ful magnet, its poles will frequently be reversed, and small steel 

 objects lying near, or which have happened to touch the poles, 

 will also become magnetised. 



When a current is made to pass round a reel, it will be found 

 to draw its core further into it. This property of the coil is 

 taken advantage of in the construction of various pieces of 

 apparatus. One example of this has already been given in 

 the construction of the electric light apparatus, explained in 

 Lesson VI. 



Another illustration of the same effect is obtained by taking 

 a bobbin (Fig. 75) with a large tube, and having connected it 

 with the battery, hold a bar of iron as, for instance, a poker 

 with the upper end just inside the bobbin, when, if the cur- 

 rent is sufficiently powerful, the poker will at once be drawn up 

 into it, and remain suspended in the middle without touching 

 the sides, thus realising the tale of Mahomet's coffin being sus- 

 pended in mid air. 



LESSONS IN ITALIAN. XXXV. 



IRREGULAR VERBS OP THE SECOND CONJUGATION. 

 I. VERBS ENDING IN ere LONG (continued). 



18. The irregular verb vedere, to see, is thus conjugated : 



INF. Simple Tenses. Pres. Veddre, to see. Pres. Gerund. Veddndo or 



veggdndo, seeing. Past Part. Veduto or visto, seen. Compound. 



Tenses. Past. Avdre veduto, to have seen. Past Gerund. Avdndo veduto, 

 having seen. 



IND. Pres. Vddo, vdggo, or vdggio ; vddi or ve' ; vdde. Vediaino or 

 veggiamo ; veddte ; vddono, vdggono, or vdggiono. Imp. Ved<5va or 

 vedda, veddvi, vedeva or vedda ; vedevamo, vedevate, veddvano. Ind. 

 Pret. Vidi, veddsti, vide ; vedemmo, veddste, videro. Put. Vedro, 

 vedrai, vedra; vedreino, vedrdte, vedranno. Cond. Pres. Vedrdi or 

 vedria, vedrdsti, vedrdbbe or vedria ; vedrdinmo, vedrdste, vedrdbbero- 

 or vedriano. 



IMP. Vddi or ve' ; vdda, vdgga, or vdggia. Vediaino or veggiamo; 

 veddte ; vddano, vdggano, or vdggiano. 



SUB. Pres. Che vdda, vdgga, or vdggia; die vdda, vdgga, vdggia, or 

 vdggi ; che vdda, vdgga, or vdggia. Che vediamo or veggiamo ; che 

 vediate or veggiate ; che vddano, vdggano, or vdggiano. Imp. Che 

 veddssi, che veddssi, che veddsse; che vedessimo, che veddste, che 

 veddssero. 



After this example conjugate the following irregular verbs : 



Antiveddre, to foresee. 

 Avveddrei, to perceive. 

 Disveddre, to neglect. 

 Diveddre, to show. 

 Malveddre, to h, \ 

 Preveddre, to foresee. 

 Provveddre, to provide. 



Ravveddrsi, to amend. 

 Riveddre, to see again.. 

 Sopravvedere, to observe 



attentively. 



Sprovvodere, to leave destitute. 

 Stravedere, to see much. 

 Travedere, to see double. 



19. The irregular verb volere, to be willing, is thus conju- 

 gated : 



INF. Simple Tenses. Pres. Voldre, to be witting. Pres. Gerund. Vol- 



dndo, being willing. Post Part. Voluto, been, willing. Compound 



Tenses. Past. Avdre voluto, to have lieen willing. Past Gerund. Avdndo 

 voluto, having been willing. 



IND. Pres. Voglio or vo' ; vudi, vuoli, or vuo" ; vuole. Vogliamo 

 voldte; vogliono. Imp. Voldva or volda ; volevi or voldi ; voldva, volda 

 or volia. Volevamo; volevate; volevano or voldano. Ind. Pret. Volli 

 volesti, voile ; voldmmo, voldste, vollero. Put. Vorrb, vorrai, vorra 

 vorrdnio, vorrdte, vorranno. Cond. Pres. Vorrdi or vorria ; vorresti 

 vorrdbbe of vorria. Vorrdmmo ; vorreste ; vorrdbbero, vorriano, or 

 vorrieno. 



(This verb, according to good Italian grammarians, has no Imperative.) 



SUB. Pres. Che voglia, che voglia, che voglia ; che vogliamo, che 

 vogliate, che vogliano. Imp. Che voldssi, che voldssi, che voldsse ; 

 die voldssirno, che voldste, che voldssero. 



After this example conjugate the following irregular verbs : 



Disvoldre, to refuse. 

 Rivolere, to wish again. 



Stravolere, to wish for too much. 

 Svoldre, to change one's mind. 



