The infinitive mood generally has at least three syllables, with the exception-I. of dá-re, to give; fa-re, to do (from the Latin facere); stá-re, to stand; di-re, to say (from the Latin dicere); gi-re and i-re, to go. II. of some contractions: bé-re, to drink (from bé-ve-re); cor-re, to gather (from có-glie-re); pór-re, to put (from pó-ne-re); scér-re, to select (from scé-glie-re); scior-re, to loose (from scio-glie-re); tor-re, to take (from lo-glie-re); trúr re, to draw (from `trá-e-re). The meanings of sentire are various to feel, hear, smell, taste; to per ceive, be sensible of; to be affected by; to esteem, judge, think; to kuow thoroughly, to dive into, etc. This conjugation comprehends, strictly speaking, three classes, of which only the first coincides in all the details with sentire. They will be explained later. This participle is formed by adding to the third person singular of the present tense the termination nte, e. g. ama, he loves:-amante teme, he fears :-temente sente, he feels-sentente. It is more used in poetry than in prose, where, in most cases, the gerund is a more efficient substitute. Many verbs have not even any present participle, because it is never used, and where it occurs it frequently partakes more of the nature of an adjective than of that of a verb, e. g. il giór-no se-guen-te, the following day; l'á-cqua bol-lén-te, the boiling water; un ca-va-lie-re er-run-te, a knight-errant; du-rán-te la guer-ra, during the war; vi-ven-le mi-o pá-dre, in the lifetime of my father; un fan-ciul-lo dor-men-te, a sleeping child; la not-te ve gnen-te, the coming night; -na ve-dú-ta ri-den-te, a pleasant, i. e. laughing prospect; car-bó-ni ar-đển-ti, live, i. e. glowing coals; for-ro ro-ven-te, red-hot iron; and some other phrases, the number of which is very limited. The present participle, like all adjectives ending in e, is of both genders, and in the plural terminates in i, e. g. un occhio lan-guén-te, ú na vó-ce lan-guén-te, a dull eye, a faint voice, pl. gli de-chi lan-guén-ti, le vó-ci lan-guén-ti. Several verbs of the third conjugation form the present participle with the termination iente, while not a few of them have no present participle at all, and many only the regular termination ente. Good writers will be the best guide. To and so are the two terminations of past participles. A regular past participle can only end in to, while the termination so is always irregular. With the exception of fa-re, to do, which doubles the t in fat-to, done, all the verbs of the first conjugation, regular and irregular, have the termination ato in the past participle. Several past participles of the verbs in are are contracted by taking away at before the last vowel o. The most frequently used of these contractions are: a-dát-to for a-dat-tá-to, adapted; a-dór-no for a-dor-ná-to, adorned; cá-ri-co for ca-ri-cá-to, loaded; chí-no, in-chi-no for chi-ná-to, in-chi-ná-to, bent; cón-cio for con-ciá-to, set off, neat; scón-cio for scon-ciá-to, spoilt, disordered; dé-sto for de-stá-to, awaked; di-mén-ti-co for di-men-ti-cá-to, forgotten, forgetful; di-mó-stro for di-mo-strá-to, demonstrated; gón-fio for gon fiá-lo, swelled; guá-sto for gua-stá-lo, spoiled; lá-ce-ro for la-ce-rá-to, lacerated; 16-go-ro for lo-go-rá-lo, worn out; pri vo for pri-rá-to, deprived; sú-zio for sa-ziá-to, satiated: scé-mo for sce-má-to, diminished; scém-pio for scem-piá-to, simple; scé-re-ro or scé-vro for sce-ve-rá-to or sce vrá to, severed; schi-fo for schi-fá-to, loathed, loathsome; sgóm-be-ro or sgóm-bro for sgom-be-rá-to or sgom-brá-to, disencumbered; spór-co for spor-cá-to. dirty; stán co for slan cá-to, weary; strác-co for strac cá-to, weary; tóc co for toc-ca-to, touched; ri-tóc-co for ri-toc-cá-to, retouched; trón-co for troncá-lo, cut off. Some of these, like adorno, desto, dimentico, lacero, sgombro, tocco, ritocco, etc. are of less frequent use in prose, others are generally La chaîne si jolie des montagnes du Taunus, qui s'étend d'un côté jusqu'au Rhin, et vient s'abaissera de l'autre2 au milieu des jardins si pittoresques de Hesse-Hombourg, offrait alors un aspect triste et désolé. Les forêts, qui partout montent et descendent avec les hauteurs et les vallons de cette contrée, ne présentaient plus à l'œil que l'éclat éblouissant du givre ou la sombre verdure des sapins. entendait le croassement du corbeau, qui laissait, en frissonnant, tomber ses plumes noires sur la neige blanche; les cerfs, bramaient, en perdant la riche parure de leur tête; les loups jetaient leurs hurlements à la portée des habitations des hommes. On Cependant, un homme enveloppé par dessus sa veste d'une redingote faite avec des peaux d'animaux tués à la chasse, s'avançait, un bâton noueux à la main, par un chemin difficile et au milieu des bois, vers un des villages situés dans les escarpements de la montagne; tout à coup, il s'arrête,10 regarde autour de lui, écoute, car des gémissements venaient de frapper11 son oreille: Peut-être, se ditil,12 est-ce la voix d'un malheureux transi de froid. Il écarte les branches du taillis 13 voisin avec son bâton, et, sur un amas de feuilles mortes, il aperçoit un vieux 14 soldat, qui, d'une voix déchirante, le prie de lui donner, pour l'amour de Dieu,15 un morceau de sa redingote pour cacher les trous de son vêtement. Ayez pitié! s'écrie l'infortuné, d'un pauvre estropié 16 qui a reçu trois blessures dans les dernières Oh! ayez guerres. pitié de moi! J'allais atteindre le prochain village," quand le froid m'a contrainte de me jeter sur ce tas de feuilles. Puisse' ma prière faire descendre sur vous et sur votre famille la bénédiction du Ciel! Ayez pitié de moi pour l'amour de Dieu! Le passant regarda un moment le vieux soldat d'un air compatissant: puis, il mit la main1s dans la poche de sa veste, en tira une pièce de trois kreutzers-c'était tout ce larmes, au pauvre homme qui tendait la main.-Dieu vous qu'il possédait lui-même-et la donna, les yeux humides de assiste! dit-il,19 car Dieu sait que je n'ai à vous donner que used in conversation. For the most part these participles by contraction lose their peculiarity as verbs, and become real adjectives, some of which, as e. g. sconcio have a great many various meanings. There is no doubt some difference between la to-vá-glia è spór-ca, the table-cloth is dirty, and la to-vá-glia è spor-cá-ta, the table-cloth is dirtied; or between só no stán co, I am weary, or tired, and só-no stan-cá-to, I am wearied. In connection, however, with the active auxiliary avere these contracted participles do not lose the peculiarities of a verb, e. g. l'ho di-mén-ti-co (for di-men-ti-cá-to), I have forgotten it (while é-gli è mol-to di-mén-ti-co means-he is very forgetful, dimentico in this instance being a real adjective); -o t' hồ di-mỗ-stro (for di-mo-strá-to), I have proved to thee; sá-zio m'a-vreb-be ciò che m'è pro pó-sto, it would have satisfied me what has been proposed to me; tóc-co (for toc cá-to) da di-vi-na i-spi-ra zió ne, moved by divine inspiration; mi só-no av-réz-zo (for av-vez-zá-to), a fár-lo, I have accustomed myself to do it, etc. But these latter cases are not frequent. Gerunds are liable to no irregularities and are indeclinable. See note to the gerund of essere. cette pauvre pièce de monnaie, avec laquelle j'allais 20 ache-enfants eux-mêmes commençaient à imiter leur mère. Après ter du pain pour le souper de ma famille; je ne possède avoir attendu plus d'une heure la fin de tous ces reproches d'autre vêtement que celui que porte. Adieu done! et que le patient mari commanda le silence, et dit alors d'une le Ciel vous aide; quant à moi, en vérité, je ne le1 puis voix ferme et énergique: Avez vous entendu' ces paroles de davantage. notre divin Sauveur ? 15-Le bien que vous avez fait au plus petit d'entre vos frères, je le regarderai comme fait à moimême, et je vous le rendrai au centuple. Eh bien! si vous avez entendu ces paroles, nourrissez-en vos cœurs et consolez-vous de ce que j'ai fait. Sur ce, le brave homme sortit,17 pour aller porter un peu de vin à son ami malade, la femme garda la maison, et les enfants allèrent cueillir 18 du bois sec aux environs. Alors cet homme poursuivit son chemin, mais d'un pas lent:21 car son cœur, ouvert à la compassion, battait avec violence; en effet, bien qu'il s'éloignât, les gémissements du vieillard continuaient de retentir à son oreille. A peine avait-il fait trente pas, qu'il s'arrêta tout à coup,22 puis rebroussa chemin, se disant en lui-même; Eh bien! soit pour l'amour de celui qui a accompli le grand sacrifice de la croix, je me résignerai aux privations les plus dures. Il y avait une heure à peine que cela s'était passé ; le Se rapprochant alors du vieillard, il se dépouilla 23 de sa re- brave homme rentrait chez lui, et ses enfants traînaient le dingote: Tenez, dit-il, enveloppez-vous de ceci; Dieu bois sec qu'ils avaient été cueillir, quand deux jeunes solm'aidera peut-être à en avoir une autre, et quand même....dats, sur le bras d'un desquels se soutenait un vieux serviSans achever sa pensée 25 il reprit son chemin. Dans la première1 chaumière du village qu'habitait le digne homme de qui avait parlé le chambellan du prince, perçait à travers le volet, la lueur2 vacillante d'une lampe. Là une mère, avec son petit garçon et sa petite fille, attendait en silence et avec inquiétude le retour du père de famille. Celui-ci avait descendu la montagne pour aller consoler un ami tombé subitement malade. Déjà la mère, tourmentée, sortait de la cabane pour prier un voisin d'envoyer son domestique au devant de son mari, lorsque le mari lui-même entra sans redingote. teur du pays, vinrent présenter des billets de logement et demander le gîte.-Ces billets ne font point mention 20 du pauvre vieux que vous voyez avec nous, dit un des soldats; car nous l'avons rencontré à peu de distance" d'ici, sur la route; il ne pouvait plus marcher pour aller regagner la jeté notre manteau sur les épaules, en lui disant de venir 22 Bavière, son pays. Il était transi de froid; nous lui avons avec nous, que nous trouverions bien quelques braves gens dans le village voisin pour lui donner l'abri et la couchée, ne fut-ce que sur un tas de paille.-Entrez, répondit le brave homme; 23 je complèterai de mon mieux votre charité; je n'ai qu'un lit :24 il sera pour le vieux; n'est-ce pas juste ? Quant à vous, mes dignes jeunes gens, vous ferez comme ma femme et moi, vous voudrez bien vous contenter de passer la nuit sur la paille. Je regrette beaucoup de n'être 25 pas plus riche, pour mieux traiter d'aussi braves soldats. SECTION IV. NOTES AND REFERENCES.-a. aller au devant, to go and meet. L'épouse voyant cela, se prit' à chuchotter et à dire: Où |—6. se prit, commenced; from prendre ; L. part ii., p. 100.— mon maris a-t-il mis sa redingote? Pour lui, il raconta tout c. L. S. 41, R. 8.-d. vêtement de dessus, upper garment.—e. L. naïvement ce qui lui était arrivé, comment, ayant encore S. 45, R. 3.-f. L. S. 41, R. 8.-g. from faire; L. part ii., p. 92. une bonne veste, il avait donné son vêtement de dessus 10 à-h. ne fut-ce que, were it only.-i. from vouloir; L. part ii., un pauvre soldat estropié, plus à plaindre que lui. p. 110. Est-il possible! s'écria la femme," donner une redingote qui t'a coûté, à toi, tant de chasses, et à moi tant de peine à coudre? Toujours, toujours donner! mais tu finiras par réduire à la mendicité, toi, ta femme et tes enfants! Etre bon, c'est bien, ajouta-t-elle; moi aussi, je veux être bonne mais une bonté sans bornes 12 n'est plus de la bonté, c'est de la faiblesse. Ce fut pourtant celle du Sauveur,13 se contenta d'abord de répondre le brave homme. 14 Cependant l'épouse continuait à se lamenter, et les petits Les deux soldats et le vieux troupier1 entrèrent dans la cabane. Le mari parla bas à sa femme, qui haussa les épaules et prit une figure de mécontentement, car il l'engageait à céder son lit au pauvre vieux. Elle y consentit;3 mais ce ne fut pas sans hésitations et sans regrets. mari cacha de son mieux la mauvaise humeur de sa femme à ses hôtes, pour que le bienfait fût accepté comme il était Le donne par lui, de bon cœur. Il fit servir un repas frugal, tel que sa pauvreté le lui permettait, et il y présida luimême en relevant la misère du service par le plus de gaieté qu'il pouvait. 9 Mais, voilà que, comme il parlait, celui à qui il devait donner son lit retira son manteau, et laissa voirs d'abord une redingote de peau de daim, celle-là même que le brave homme avait donnée1 le matin, et qu'il reconnut sans peine. -Me voici!.... moi.... le pauvre estropié, qui ai reçu la redingote!.... Vous souvenez-vous ?-Oui, répondit avec étonnement le maître du logis, mais comment ses fait-il 10 que vous ayez eu besoin, en outre, du manteau de ces dignes jeunes gens ?-Comme j'ai eu besoin du vôtre,11 repartit le vieux soldat. Et en même temps il retira aussi la redingote de peau de daim, et il laissa voir aux regards éblouis,12 un riche vêtement brodé d'or.-Me reconnaissez-vous? Je suis le landgrave de Hesse-Hombourg; j'avais entendu 13 parler de votre charité, j'ai voulu la mettre moi-même à l'épreuve, pour vous en récompenser, si elle était telle qu'on me le disait. Ces braves soldats m'ont aidé1 en dernier lieu dans mon innocent stratagème. Je prends désormais, vous, votre femme et vos enfants sous ma protection spéciale. Je veux qu'à la place de cette pauvre chaumière, s'élève pour vous et pour eux une maison simple, 16 mais honorable, qui perpétuera le souvenir de la charité récompensée. J'y viendrai plus d'une fois visiter mes protégés. Je garde la redingote de peau de daim que j'ai reçue; mais, dès demain, ma femme enverra,18 à la place, de bons habits pour toute la famille. En attendant que Dieu vous donne aussi ses récompenses dans le ciel, continuez à le servir 19 par celle de toutes les vertus qu'il aime le mieux, la charité. En achevant ces mots, le prince déposa 29 un rouleau de pièces d'or sur la table, et sortit avec les deux soldats, laissant la famille dans une grande stupéfaction. Maintenant, ma femme, et vous mes enfants,22 s'écria le brave homme en pleurant de joie, êtes-vous satisfaits ? La femme n'osait répondre, tant la honte et la joie paralysaient à la fois ses facultés. Le mari sourit; puis il ajouta Cet or ne nous a pas été donné pour nous seuls; réjouissons nous de l'avoir, autant pour le faire partager aux malheureux, que pour nous en servir nous-mêmes; et songeons que notre devoir 23 est de faire bénir partout le nom de notre bienfaiteur. LE CHENE ET LE TOURNESOL. AUPRES d'un jeune chêne, espoir d'un beau jardin,' Mais dont la tige frêle et le rare feuillage Sur quelques palmes de terrain Traçaient à peine leur ombrage, Un tournesol tranchait de l'important;3 Et fier de sa prompte croissance Etalait avec arrogance De ses soleils dorés le panache éclatant. -Vois, disait-il au jeune chêne, L'été qui m'a fait naître est encore radieux,5 Et ma tête s'élève au-dessus de la tienne; Quatre saisons de plus, et j'atteindrai les cieux. Mais toi, race d'arbuste, à ramper condamnée, Le plus hardi joûteur n'oserait t'opposer Au râteau du manant qui me vient arroser; Et cependant trois fois tu vis naître l'année.d 1. Comment Viennet appellet-il le chêne ? 2. Que dit-il de la tige et du feuillage? 3. Que faisait le tournesol ? 4. Qu'étalait-il avec arrogance? 5. Que disait-il au jeune chêne? 6. Que dit-il à l'égard de sa tête ? 7. Que dit-il de quatre saisons? 8. A quoi, selon lui, le plus hardi joûteur n'oserait-il ople chêne? poser 9. Que dit-il de l'âge du chêne? 10. Quel fut le commencement de la réponse du chêne? 11. Que dit-il de sa durée ? VIENNET. NOTES AND REFERENCES.-a. L. S. 30, R. 8.-6. tranchant de l', played the.-c. this line presents a poetical inversion; the prose construction is: le panache éclatant de ses soleils dorés.d. naître l'année, the year renewed.e. from aller; L. part ii., p. 76.-f. L. part ii., § 39, R. (5).-g. soleils, flowers.-h. grandis, extolled; literally, grown.-i. traiter, call.j. from vivre; L part ii., p. 110. ON PHYSICS, OR NATURAL PHILOSOPHY. No. XLVI. (Continued from page 289.) OPTICS. REFLECTION OF LIGHT. Laws of Reflection.-When a luminous ray meets a polished surface, it is reflected, that is, bent backwards, in accordance with the following laws, which are, mutatis mutandis, the same as the laws of the reflection of caloric. 1st. The angle of reflection is equal to the angle of incidence. 2nd. The incident and reflected rays are in the same plane, which is perpendicular to the reflecting surface. The words incident ray, reflected ray, angle of incidence and angle of reflection are here to be taken in the same sense as they were employed in the Lessons on Caloric, see p. 66. The two laws just enumerated are proved by means of the apparatus represented in fig. 253. Fig. 253. This is a graduated circle, of which the plane is vertical, mounted on a stand. Two copper rules moveable round the centre are fitted with screens, the one of ground glass P, and the other opaque c, but having a small aperture in the middle of it. At the extremity of the rule at c is placed a mirror i, which can be adjusted at any angle to the rule, but is always perpendicular to the plane of the graduated circle. At the centre of the circle is placed a small plane mirror м, which is also exactly perpendicular to the plane of the circle. In making an experiment, a pencil of solar light s is received on the mirror 1, which is inclined at such an angle that the reflected light passes through the screen c and falls on the centre of the mirror м. Here, the luminous pencil undergoes a second reflection and takes a direction м P, which is ascertained by moving the screen P until the image of the aperture o is formed in the centre of it. Reading off then from the limb or edge of the circle the number of degrees comprised in the arcs AC and AP, we find that these numbers are equal, which proves that the angle of reflection AMP is equal to the angle of incidence AMC. The second is proved by the actual arrangement of the apparatus, since the plane of the rays CM and MP is parallel to that of the graduated circle, and consequently perpendicular to the plane of the mirror м. REFLECTION FROM PLANE SURFACES. Mirrors and Images.-Bodies having polished surfaces, such as metal or glass, from which objects presented to them can be seen by reflection, are called mirrors. The place where these objects appear is called their image. According to their form, mirrors are distinguished into plane, concave, convex, spherical, parabolic, conical, etc. mirrors. The images formed by these mirrors are twofold, virtual and real. Plane Mirrors.-The determination of the position and magnitude of the images of objects, depends on that of the 'images of a series of points in them. Let it first be required VOL. V. mirror м N, and produce the ray oв behind the mirror till it meet the perpendicular AN produced in the point a, the two triangles ABN and B Na will be equal. For the angles A B N and N Ba are equal, each being equal to the angle o в M, and the angles ANB and B Na are equal, each being a right angle; and the side BN is common to both triangles. Therefore a N is equal to AN; that is, a luminous ray A B takes, after reflection, a direction such that its production behind the mirror cuts the perpendicular Aa in a point a situated exactly at the same distance from the mirror as the point A itself. This property belonging to every luminous ray, is applicable also to the ray AC proceeding from the same point A. From this illustration, we deduce the important principle that all the rays emitted from the point A, and reflected from the mirror, follow, after reflection, the same direction as if they proceeded from the point a. This is the reason why the eye is deceived, and perceives the point A at a as if it were really placed at that point. Therefore, in plane mirrors, the image of a point is situated behind the mirror at a distance from it equal to that of the given point, and on the perpendicular drawn from this point to the mirror. In the same way the place of an image of any object may be determined by finding, according to this rule, the image of each of its points, or at least of those which are sufficient to determine its position and form. Fig. 255 shows the construction that must be adopted in order to obtain the image ab of any object A B. From this construction we at once conclude that in plane mirrors the image is of the same size as the object; for if we turn over the trapezoid ABCD upon the ¡trapezoid a b c D, it is plain that they will coincide with each other, and that the object A B will coincide with its image a b. It follows also from the same construction that, in plane mirrors, the image is symmetrical with the object, and not inverted; and here the word symmetrical has the same meaning as in geometry, when we say that two points are symmetrical with relation to a plane when they are situated on the same perpendicular to the plane and at equal distances from it, the one being on the one side of the plane, and the other on the other side of it; and these conditions are successively satisfied by all the points of the object A B, and of its image ab. Real and Virtual Images.-In the reflection of luminous rays 124 from plane mirrors, two cases arise according as the reflected rays are divergent or convergent. In the former case the reflected rays never meet; but if we conceive them to be produced on the other side of the mirror, their produced parts, or prolongations, will meet in the same point as shown in the two preceding diagrams. The eye then considering these rays as if they proceeded from this point, sees the image there. But the latter has no real existence, since the luminous rays do not pass to the other side of the mirror; this is, therefore, only an optical illusion, and therefore the name of virtual image only is given to the appearance, as being only such, and not a reality; and this is always the nature of the images given by plane mirrors. In the case where the reflected rays are convergent, an example of which we shall soon see in concave mirrors, these rays meet in a point situated in front of the mirror, and on the same side of it as the object. There they form an image called the real image, in order to express the fact that it really exists, for it can be received on a screen and made to act chemically on some substances. In short, it may be said that real images are those which are formed by the reflected rays themselves, and virtual images are those which are formed by their prolongations. Multiple Images. When an object is placed between two mirrors which form a right or acute angle with each other, it produces images whose number increases with the inclination of the mirrors. If they are placed first at a right angle, three images will be seen, as shown in fig. 256. Fig. 255. The rays oo and o D proceeding from the point, give, after one reflection, the images o' and o" respectively; and the ray OA, which undergoes two reflections at A and B, give the third image o"". When the angle between the mirrors is one of 60°, five images are formed; and when the angle is 45°, seven images are formed. The number of images continue thus to increase in proportion as the angle of the mirrors diminishes; and when it is zero, that is, when the mirrors are parallel, the number of images is theoretically infinite. This multiplicity of images arises from the fact that the luminous rays undergo successively from the one mirror to the other an increasing number of reflections. On this property of inclined mirrors is founded the construction of the kaleidoscope, an apparatus formed of a pasteboard tube, in which are placed two mirrors inclined at an angle of 45°. If some very irregularly formed objects, such as moss, tinsel, or lace, be placed at the one extremity between two plates of glass, of which the exterior is ground, and they be looked at through the other extremity of the instrument, these objects and their seven images will be seen symmetrically arranged, and presenting to the eye a very diversified and agreeable variety. Glass Mirrors.-Metallic mirrors having a single reflecting surface, produce a single image only; such, however, is not the case with glass mirrors. These produce several images, which may be easily seen, when we look at the image of a candle in a glass. We see the first image not very intense, then a second very distinctly, and behind these several others whose intensity successively diminishes until it become nothing. This phenomenon is explained by the operation of the two reflecting surfaces which are presented by glass mirrors. When the luminous rays meet the first surface, a part of them is reflected, and gives the first image a, fig 257, formed by the prolongation of the rays be reflected double the thickness of the glass, but it is more intense than it, because the metallic foil which covers the second face of the mirror reflects more than the glass. As to the remaining images, they are less and less intense, because the rays which produce them emerge after a series of reflections on the two interior faces of the mirror. As this multiplicity of images would injure the observations made by means of several optical instruments, metallic mirrors are usually employed. Irregular Reflection.-The reflection which takes place at the surface of polished bodies, according to the laws already laid down, is recognised by the name of regular or specular reflection; but the quantity of light thus reflected, does by no means represent the incident light. This light, when the reflecting body is opaque, is really divided into three parts, 1st, the part which is regularly reflected; 2nd, the part which is reflected irregularly, that is, in all directions; and 3rd, that part which is destroyed or absorbed by the reflecting body, in a manner similar to the caloric which becomes latent in the changes from one state to another. If the body which receives the incident rays be transparent, there is more than a fourth part of the light which passes through it. The light reflected irregularly is designated by the name of diffused light; it is this light which enables us to see bodies. In fact, the light regularly reflected does not give the image of the bodies which reflects it, but rather that of the body which emits it. For example, if we admit into a dark room a pencil of solar light on a well-polished mirror, the better that the light is regularly reflected from it, the less visible will be the different parts of the surrounding medium. The eye which then receives the reflected pencil does not see the mirror but only the image of the sun. If we weaken the reflecting power of the mirror by throwing some light powder upon it, the quantity of the diffused light increases, the solar image is diminished, and the mirror becomes visible from all parts of the room. Intensity of Reflected Light.-In bodies of the same kind, the intensity of the regularly reflected light increases with the degree of polish, and with the angle which the incident rays make with the normal (or perpendicular) to the reflecting surface. For example, if we look very obliquely at a leaf of white paper placed before a candle, we perceive, by reflection, an image of the flame; but this phenomenon does not take place when the eye receives from it rays that are less oblique In bodies of different kinds, polished with the same care, the angle of incidence being the same, the intensity varies with the substance; it varies also with the medium in which the reflecting body is placed. For example, polished glass immersed in water loses a part of its reflecting power. REFLECTION FROM CURVED SURFACES. Spherical Mirrors.-There are various kinds of curved mirrors; those which are the most frequently in use are spherical and parabolical mirrors. Those mirrors of which the curvature is that of a sphere, are called spherical mirrors. This surface may be considered as generated by the revolution of an arc MN, fig. 258, about the radius CA, which joins the middle of the arc and the centre of the circle of which it is an arc. According as the reflection takes place on the interior or the exterior face of the mirror, that is, on the same side of the arc M N as the centre, or on the opposite side of it, so |