2V4 



THE POPITLAE EDUCATOB. 



etrongly negative. A similar star appears at the end of a wire 

 inserted in the negative conductor, and thus the appearance 

 of a star or a brush enables us to discriminate between posi- 

 tive and negative electricity. So powerful is the influence 

 exerted by a point, that one, even at a distance of several feet, 

 will seriously diminish the power of the machine. 



Soon after the invention of the electrical machine, the idea 

 of storing up the electricity suggested itself ; and one of the 

 early electricians, finding that water was a conductor, filled a 

 bottle with it, and passed a wire through the cork, that by 

 means of it he might cause the electricity to enter. Having 

 held the end of this wire to his machine till he thought the 

 bottle was full, he attempted to remove the rod lest the elec- 

 tricity should escape by it ; but on doing so, to his intense alarm, 

 he received a shock so violent that he kept his bed for a 

 ehort time, and declared that nothing should ever induce him to 

 repeat the experiment. The news of it, however, spread, and 

 many others repeated it with various modifications ; and thus 

 the Leyden jar, so called from the place where the experiment 

 was first tried, was constructed. 



To make a Leyden jar (Fig. 11), take a wide-mouthed glass jar 

 (one of those used by confectioners for sweets will answer well), 

 and carefully coat it inside and outside with tinfoil to within about 

 two or two and a-half inches of the top. Cut a large bung, or, 

 better still, turn a cover of baked mahogany, to fit its mouth, 

 and through this fix a piece of brass wire carrying a ball on its 

 upper end. From the inner end of this wire let a short piece 

 of chain reach to- the bottom of the jar. In some jars the wire 

 at the top may be bent over like a hook, so that they can be 

 suspended from the conductor. 



If the jar be now held with its knob close to the conductor, 

 sparks will pass in for a little time till the jar becomes filled. 

 Now set it down, and, taking a piece of wire bent into a curve, 

 touch the outside of a jar with one end, and bring the other so 

 as to touch the knob. A bright spark, accompanied by a loud 

 crack, will at once be seen, showing that the jar has discharged 

 itself. 



For a small jar, one of the bottles that are used by chemists 

 ror holding quinine may be used, as they are usually made of 

 thin glass. The shock from one of these will be as powerful 

 as most people will care to take. With an ordinary narrow- 

 mouthed bottle there is a difficulty, arising from the impossibility 

 of coating it inside with tinfoil. To obviate this, it has been 

 suggested to pour some thick paste into the bottle, turning it 

 about so as to wet the interior, and then put in a number of 

 brass or iron filings. These will adhere and form a conducting 

 coating ; but though a considerable shock may be obtained from 

 a jar thus prepared, there is an objection to the plan, arising 

 from the fact that the particles are not in absolute contact, 

 nnd therefore, after the jar has been discharged, a second and 

 even a third shock may be obtained from it, each, of course, 

 much feebler than the first. 



To take the shock, one hand should bo placed against the 

 outer coating, and the other, or a wire held in it, brought near 

 the knob. Any number of persons can join hands, those at the 

 ends of the chain touching the outside and the knob respectively, 

 and the shock will be equally felt by all. Sometimes, when it is 

 desired to discharge a large jar, or to send a shock through any 

 substance, the jointed discharger represented in Fig. 12 will be 

 found very useful. The handles are of glass, and thus prevent 

 any portion of the shock being felt by the operator/ The 

 reason why, in discharging a jar with this, one knob should 

 be brought into contact with the outer surface before the other 

 touches the ball, is that if the spark passes against the side of 

 the jar it may break it. As electricity always chooses the best 

 conductors to pass along, it is not necessary for discharging a 

 jar to have glass handles ; a pioce of wire may be used and 

 held in the hand without any shock being felt. For many pur- 

 poses, however, the insulating handles are a great advantage, 

 and they can be made of gutta-percha instead of glass, if more 

 convenient. 



The Leyden jar is merely an illustration of the principle of 

 induction already referred to. The glass is di-electric, and the 

 metallic coatings serve to distribute the electricity over its sur- 

 face. As soon as the interior becomes positively charged, it 

 acts by induction on the exterior, driving off from it an 

 amount of positive electricity noarly equal to that which it has 

 received. Hence, if we suspend the jar from the conductor, 



or place it upon a common glass tumbler or other insulating 

 support, we shall be able to take sparks from its exterior. 

 If no means be provided for this electricity to escape, wo shall 

 be unable to charge the jar. 



In their normal state the coatings contain a definite amount 

 of electricity, and if there be an excess added to one side, the 

 other must lose a corresponding amount. The spark and the 

 shock are merely the effects by which the restoration of 

 equilibrium between the two sides is manifested. 



A striking illustration of thi? principle is seen if we place a 

 number of jars so that the knob of one is connected with the 

 outside of the next. This may be done by supporting them 

 on their sides on insulating stands, or by laying them on pieces 

 of glass. If now we connect the knob of the first with the 

 conductor, and the outside of the last with the ground, each 

 of the series will bo charged, the electricity given off from 

 one charging the next. The charge in the last will, however, 

 be rather weaker than that in the first, owing to the thickness 

 of the glass slightly interfering with the induction. This 

 mode is called "charging by cascade;" and if the jars are 

 afterwards placed together on an insulating substance, so that 

 their outsides may touch, and a wire be so arranged as to 

 connect all their knobs, a very powerful shock will be produced. 

 Great care must, however, be taken in doing this to guard 

 against the shock being accidentally taken, as it would certainly 

 be too strong to be pleasant. 



LESSONS IN LATIN. XLII. 



DEVIATIONS IN THE FOURTH CONJUGATION. 



1. Perfect in -ivi and-vi ; Supine in -TUM. 

 i. Sepelio, sepelire, sepelevi, sepultum, bury, inter (E. U. 

 sepulture). 



ii. Salio, salire, salui (no supine), to leap (E. R. salient). 

 Compounds : silio, silire, silui, sultum ; as, assilio, assilire, 

 assilui, assultum, (o spiking at. 



2. Perfect in -i ; Supine in -TUM. 



i. Comperio, comperire, comperi, compertum, to experience, to 

 find by experience. 



ii. Reperio, reperire, reperi, repertum, to find. Aperio has 

 aperui, aperire, apertum, to open (E. R. aperture). Operio and 

 co5perio, to cover, have -rui, -rtum. 



iii. Venio, venire, veni, ventum, to come. 



3. Perfect in -si ; Supine in -TUM. 



i. Amicio, amicire (amixi and amicui, both rare); amicturn. to 

 clothe. 



ii. Farcio, farcire, farsi, fartum, to stuff. Compounds in 

 f ercio, f ersi, f ertum, as refercire, to stuff quite fully. 



iii. Fulcio, f ulcire, f ulsi, fultum, to prop, to support. 



iv. Haurio, haurire, hausi, haustum, to draw up, drink. 



v. Sancio, sancire, sanxi, sancitum (more seldom sanctum ; 

 sanctus, -a, -um, as an adjective, holy), to consecrate, confirm. 



vi. Sarcio, sarcire, sarsi, sartum, to repair, make good, replace. 



vii. Sepio, sepire, sepsi, septum, to hedge in. 



viii. Vincio, vincire, vinxi, vinctum, to bind, put into chains. 



4. Perfect in -si ; Supine in -SUM. 



i. Sentio, sentire, sensi, sensum, to feel, to be of opinion. 

 VOCABULARY. 



EXERCISE 161. LATIN-ENGLISH 



1. Regis sepulchre lisec verba inscripta aunt, " Probe vixit, imprSbos 

 vinxit, hostes vicit." 2. Hostes victi et catenis vincti in servitutem 

 abducti sunt. 3. Imperium justis legVbus fultutn esse debet. 4. Rex, 

 pace composite, rempublicatn labefactam sua virtute fulsit. 5. Virtus 

 difficilis inventu est, rectorem ducemque desiderat. 6. Artea innu- 



