he time during which a condim scusative without a preposition Ρίπεο. απέχει ή Πλάτος Platea is seventy stad Σε μείνατε ταυτην την remain this day. EXERCISES G Ο Φωκικός πολεμος α πλευσεν. Σωκρατης, η η Ε αύην, περὶ παντων μαλλι - Ξ τελος άρκωσε παντας τους σε στα χρη μιμήσεις πονηρας και επτον ονομαζει πατης και τις δικαιος όντως ην. Ελλάδα δε τα μέγιστα τους Η Δανία έκαστην διελείν πελα και θεραπεύοντας αυτήν τη πηρα πει τι κακόν εργάζονται τα τα κακα είπεν ανθρωπους Ι και πολύ αγορεύει. Ταυτα, με τον φροντιστέον ὁ τι ερούσι ως TEE GAMES τα μη καλώς εχοπτ κουσιν οἱ τεχνῖται ὁ οἱ διδασκαλ να τους παϊδας παιδευονται τ αληθίζεσθαι Αναμνησα να ετεριας κινδύνους. Ότι σε κου της των φίλων τύχας. τοῖσι, πολλοι δε ἱμάτια. Ταγαρτ -την ανδεια των συναντων επίμα ATTENT BUT THPT - I might live at thou mightst that he might live mo, that we might ste, that you might live éssero, that they might LVC anish are such as do not conform of conjugation to the model verbs ...e deviations of each irregular verb slight, yet important to be known, as verbs are in general use. ne of the different irregular verbs: seven on, seventeen of the second, and fifteen of of these differ but very slightly from each rregular verbs are conjugated like some one Line forms. Four of these, haber, ser, estar, and cady been conjugated. bs which undergo slight changes in the verb-roots ings of certain tenses or persons of tenses, are not account deemed irregular, since these changes take Jely to preserve regularity and uniformity of sound, would be dissimilar in some cases if these changes did ake place. Thus, as before mentioned, buscar, pronounced kar, would, in the present tense of the subjunctive mood, it no change of letters should occur, be busce, pronounced Loos'-thay (c before e and i being sounded like th in thin), and to preserve the hard sound of c, this latter is changed into qu; thus, busque, pronounced boós'-kay. Both regular and irregular verbs undergo such changes when required by the rules of pronunciation. Remark. In the following conjugations of the irregular verbs, those persons of the moods and tenses only which deviate from the regular conjugation are given. Thus, in the first verb, andar, no tense of the indicative mood except the perfect definite is given, because this verb is conjugated regularly in the other tenses of this mood. In the second verb, contar, the first and second persons plural of the present indicative are not given, because these persons are regular. The student is therefore to remember that all moods, tenses, and persons not included in the conjugation are regular. We have, however, in all cases given the participle and gerund, whether formed regularly or not. CONJUGATIONS OF IRREGULAR VERBS. 1st Conjugation. Andar, to walk. ON PHYSICS, OR NATURAL PHILOSOPHY. No. LXX. (Continued from page 668.) DYNAMICAL ELECTRICITY. PHENOMENA OF INDUCTION. Effects of Tension produced by Currents of Induction.-M. Ruhmkorff has lately constructed some very powerful bobbins, by means of which not only violent shocks may be produced by currents of induction, but also luminous effects very strongly resembling those of electrical machines of strong tension. This apparatus consists of a strong bobbin B (fig. 465), placed vertically upon a thick plate of glass, which isolates it. The bobbin, which is about six inches high, is formed of two wires-one thick, about one-twelfth of an inch in diameter, and making three hundred turns; the other fine, being only about-an eightieth of an inch in diameter, and rolled round the former ten thousand times. These wires are not only covered with silk, but each coil is isolated from the next by a layer of gum-lac varnish. It is the thick wire which is the inductor. The current which passes through it is simply that of a Bunsen battery. The positive pole of the battery being in connexion with the wire PH, the current passes through the conductor c to a cylinder G; thence it descends by a metallic part g, and reaches a copper plate F, which conducts Fig. 465. duced in the thin wire. Now this latter being completely isolated, the induced current acquires so great a tension that it is capable of producing very intense luminous effects. For this purpose, the two ends of the fine wire, qy and px, which come out from beneath the glass plate, are connected with the two rods attached to a globe M, such as has been already described under the title of the electrical egg, and is employed to observe the luminous effects of an electrical machine in a vacuum. Having produced a vacuum in the globe, a beautiful luminous trail is produced from one end to the other, apparently unbroken, and of the same intensity as is obtained with a powerful electrical machine, the plate of which is turned rapidly. It is the positive pole of the induced current which exhibits most brightness. Its light is red, while that of the negative pole is feeble and of a violet colour, and extends throughout the whole length of the negative rod, a phenomenon which does not take place at the positive pole. Messrs. Masson and Breguet made the first experiment to show that a bobbin of induction is capable of producing the physiological effects of the Leyden jar; but it was M. Ruhmkorff who first, having completely isolated the induced current by means of the above bobbin, was enabled to obtain from it electricity of any tension, and to produce effects of light such as have just been described. Stratification of Electric Light.-In studying the electric light obtained from M. Ruhmkorff's bobbin of induction, M. Quet has lately observed, that if we do not produce a Fig. 466. it to one of the extremities v of the thick wire of the bobbin. The other end of the wire terminating at i, in one of the copper supports of the glass plate, the current, on leaving the bobbin, proceeds to a second plate c, whence it ascends in an iron column A. There the current reaches an oscillating hammer a (fig. 466), which is sometimes in contact with a conductor n, and sometimes separated from it. When contact takes place, the current proceeds along the conductors n and E (fig. 465), as shown by the arrows, ascends into the cylinder G, and thence returns to the battery along the conductor d and the wire a. With regard to the motion of the hammer a backwards and forwards, that is produced by a soft iron cylinder ro, placed in the axis of the bobbin. When the current of the battery passes along the thick wire of the bobbin, this iron is magnetised, and draws up the hammer a-which is also ironfrom below. The current then being interrupted, since it connot pass through the part n, the cylinder or loses its magnetic properties, and the hammer a falls down again. At this moment the current recommences, the hammer a is again raised, and so on continually. As the current of the battery passes thus interruptedly along the thick wire of the bobbin, at each interruption a current of induction, successively direct and inverse, is pro VOL. V. vacuum in the globe м (fig. 466), till after having introduced into it essence of turpentine, spirits of wine, etc., the appearance of the light is completely altered. It then appears under the form of a series of zones, alternately bright and dark, forming a sort of pile of electric light between the two poles (fig. 467). In this experiment, it follows, from the discontinuity of the current of induction, that the light is not continuous, but consists of a series of discharges nearer to each other, in proportion as the hammer a (fig. 466) oscillates more rapidly. The luminous zones then appear affected with a rapid doublerevolving and undulatory motion. M. Quet considers this motion as an optical illusion, because, if the hammer be made to oscillate slowly with the hand, the zones appear very distinct and fixed; but the phenomenon is then too instantaneous to allow the undulations to be perceived, if there are any. The light of the positive pole is, as we have said, generally red, and that of the negative pole violet; but the colour varies with the vapour or gas which is in the globe. M. Despretz has lately observed that the phenomena established by Messrs. Ruhmkorff and Quet with a discontinuous current may be produced with an ordinary continuous current, but with this important difference, that the continuous current requires a great number of Bunsen couples, while the 148 discontinuous current of M. Ruhmkorff's bobbin requires only one. It is a remarkable fact, established by experiment, that the intensity of the effects of this bobbin increases very little when the number of Bunsen couples is increased. Fig. 467. The theory of the phenomena of the stratification of electric light in vapours, and the colouring of the poles, is not yet ascertained satisfactorily. Characters of Currents of Induction. From the various experiments upon currents of induction to which we have called the reader's attention, we see that, in spite of their instantaneous duration, they possess all the properties of ordinary voltaic currents. Like them, they produce violent physiological, luminous, calorific, and chemical effects, and themselves give rise to fresh induced currents. Lastly, they deflect the needle of galvanometers and magnetise steel bars, when they are passed along a copper wire wound round these bars in the form of a helix (fig. 452). The shock of induced currents is much more intense than that of hydro-electric currents. The latter, indeed, do not give any shock except with a large number of couples, while a single Bunsen couple, with the bobbin, above described (figs. 456 and 461), produces induced currents, the shock of which is insupportable and even dangerous when prolonged. The shock is entirely owing to the direct current, that is to say, to that which is produced when the current in the inducing wire is interrupted. The intensity of the shock of induced currents renders their effects like that of electricity in a state of tension. However, as they always act upon the galvanometer, it is probable that in the wires subjected to induction, there is electricity both in a state of tension and in a dynamical state. The direct and inverse induced currents have been compared together in three points of view: the violence of the shock, the magnitude of the deflection in the galvanometer, and the magnetising action upon steel bars. Thus examined, these currents exhibit very different results. They appear nearly equal in respect of the deflection of the galvanometer, while the shock of the direct current being very violent, that of the inverse current is almost imperceptible. There is the same difference with regard to the magnetising power. The direct current magnetises powerfully, but the inverse current does not magnetise at all." PRACTICAL APPLICATIONS OF THE GALVANIC BATTERY. Electric Telegraphs.-We now come to a subject in which all are interested, and with which all are in some degree familiar, though comparatively few understand it thoroughly. Of all the scientific marvels wrought in this remarkable century, there is none more astounding than the electric telegraph, which enables us to convey communications to persons hundreds of miles off with all the rapidity of the lightning flash, whether they be in the same country or separated from us by miles of ocean waves. This achievement eclipses all the wonders accomplished by the application of steam, and is in itself sufficient to render the present century for ever memorable in the annals of our race. Electric telegraphs, we need scarcely say, are apparatus which serve for the transmission of messages to great distances, by means of voltaic currents along metallic wires. Even last century, philosophers had entertained the idea of correspond. ing at great distances by means of the effects produced by the electricity of electrical machines, and propagated along con ducting wires. In 1814, Sommering invented a telegraph based upon the decomposition of water by the battery, which he employed a means of indicating signals. In 1820, at a time when the electro-magnet was not known, Ampère, guided by Ersted's experiment, proposed to correspond by means of magnetised needles, above which a current was directed, employing many needles and as many wires as there are letters in the alphabet. In 1837, M. Steinheil, at Munich, and Professor Wheatstone, in London, constructed telegraphs with severa wires, each acting upon a magnetised needle, the source of the current being a Clarke's electro-magnetic apparatus, or hydro-electrical battery. But the telegraph could not be made simple enough, till Professor Wheatstone, in 1840, introduced the use of electro-magnets. Without altering the principle of the electric telegraph, its form has been much changed; but all the forms may referred to three classes-the dial telegraph, the signai tele graph, and the writing telegraph. We proceed to give so account of each of these varieties. Fig. 468. The Dial Telegraph.-There are several sorts of dial tele graphs. That which is represented in figs. 468 and 469 was constructed by M. Froment, and our drawings were made in June, 1850. M. Froment's telegraph is the same in principle as those employed on railways. Like them, it consists of two distinct apparatus, one called the manipulator, for transmitting signals, and the other the receiver, for receiving signals. The former is connected with a carbon pile or battery a, and the two apparatus are connected together by means of two metallic wires, either iron or copper, the former of which goes from The following is the course of the current in the two apparatus and the effects which it produces. From the battery it proceeds along a copper wire A (fig. 468) to a piece of brass N in contact with a metallic wheel R, passes into a second piece M, and then into the wire o, which joins the other station. There the current goes into the bobbin of an electro-magnet b, concealed in fig. 469, but represented in profile in fig. 470, Fig. 470. F mits it to a ratchet-wheel a, the axis of which carries the indicating needle or pointer. The teeth of the wheel are so bent that it is always moved in the same direction by the fork, which is indispensable to the usefulness of the apparatus. To understand the intermissions of the electro-magnet, we have recourse to fig. 468. The wheel R has twenty-six teeth, twenty-five of which correspond to letters of the alphabet, and the last to the interval reserved between the letters A and Z. When, by holding the button P in the hard, you turn the wheel R, the end of the piece N is, by its curvature, always in contact with the teeth. The piece м, on the contrary, has a cog at the end, cut in such a way that there is contact and interruption of contact in succession. Consequently, the communications with the battery being established, if you move forward the needle r four letters, for example, the current passes four times from м to N, and is interrupted four times. The electro-magnet of the distant station will therefore become attractive four times, and will cease to be so four times. Consequently, at last the wheel & will have turned four teeth, and as each tooth corresponds to a letter, the needle of the distant station will have gone over exactly the same number of letters as that at the station of departure. With regard to the part s, represented in both figures, it is a piece of copper moveable upon a hinge, and serving to interrupt the current or close it at will. From what has been stated, it is easy to understand how correspondence is carried on from one place to another at a distance. Suppose, for example, the first apparatus (fig. 468) to be in London, and the second (fig. 469) at Birmingham, and the communication between the two stations being established by means of wires, we wish to transmit from London to Birmingham the word signal. The needles of the two apparatus being both at the interval between A and Z, the person who sends the despatch moves forward the needle P to the letter S, where it stops for a very short time; the needle of the apparatus at Birmingham, faithfully following the movements of the needle in London, stops at the same letter, and then the person who receives the despatch marks this letter. He who is in London, continuing to turn the needle always in the same direction, stops the needle at the letter I, and the other needle instantly stops at the same letter. Proceeding in the same manner for the letters G NA L, the whole word is soon transmitted to Birmingham. To call the attention of the person to whom we are about to make a communication, a bell is fitted up at the distant station, and is connected with the current whenever the correspondence is suspended. A trigger, moved by the electromagnet, rings this bell directly the current passes, and thus gives a signal that a message is about to be communicated. Further, each station ought to be provided with the two apparatus above described (figs. 468 and 469), otherwise it will be impossible to return an answer. We have supposed that the current which goes from London to Birmingham returns in the same way from Birmingham to London. But this second wire is useless. Experience has shown that, if the positive pole in London is connected with the apparatus, and the negative pole with the earth, it is sufficient for the conducting wire which goes to Birmingham to be there connected with the earth. It is generaly believed that the circuit is then closed by the earth through which the current returns from Birmingham to London. This hypothesis has been severely criticised by some philosophers, particularly by the Abbé Moigno, in his treatise on the electric telegraph. And indeed it is difficult to conceive that, on its arrival at Birmingham, the current, which by its nature tends to disperse in all directions, should choose precisely that which takes it back to the battery whence it started. M. Moigno absorbs at the two ends of the wires the electricity which the considers that the earth, acting in this case as a reservoir, battery transmits, and the consequence is, that there is the same continuous current in the wire as if the two ends touched each other. which shows the hinder part of the apparatus. This electromagnet is fixed horizontally at one of its extremities, and by the other it attracts a soft iron armature a, which forms part of a bent lever moveable about its point of support o, while a coiled spring tends to move the lever in the contrary direction. When the current passes, the electro-magnet attracts the lever a c, which, by means of a rod i, acts upon a second lever d fixed to a horizontal axis, which is itself attached to a fork F. When the current is interrupted, the spring r draws back the L'objet de la science est de connaître la vérité; son occupation, de lever a c, and with it all the parts of the apparatus depending la rechercher; son caractère, de l'aimer: les moyens de l'acquérir sont upon it. The result of this is a motion backwards and de renoncer aux passions, de fuir la dissipation et l'oisiveté.-J.J forwards, which is communicated to the fork F, which trans-Rousseau. |