of St. James, where he was accredited as Russian ambassador. She soon became as conspicuous in London as she had been in Berlin, her diplomatic manœuvres aiding not a little her husband, as they did also Pozzo di Borgo and Gentz, who came to London between 1812 and 1814 on a special mission from the Austrian government. In 1815 she was one of the most prominent of the many distinguished persons who attended the congress of Vienna, and many of her intrigues there were said not to have been exclusively of a political nature. The princess of Lieven, the princess Zanaide Volkonski, and the grand duchess of Oldenburg (sister of Alexander I.), were the great rivals for beauty and genius in Viennese society, and they were called "the three graces." From that time until 1834, when the prince was recalled to St. Petersburg, Mme. Lieven held a leading position in the highest political and social circles of London, where she competed eagerly for the honors of superior diplomatic skill with Talleyrand, then for a time French ambassador in England, and more particularly with his accomplished and crafty niece the duchess of Dino. Her saloon in London was a curious laboratory in which she endeavored to color and shape all political elements in accordance with the autocratic system of government, of which Russia was then the chief exponent. No sooner did a public question of English or European interest arise than the princess applied all the many resources of her cunning and plotting disposition, in order to derive from it some benefit for her imperial master, or to engraft upon it Russian political idiosyncrasies. During the agitation in England in regard to the Grecian struggle for independence, she was on the side of the Philhellenists, not from any sympathy with liberty, but with a view of strengthening Russia by weakening Turkey. She was active among those who conspired against the establishment of Belgium as an independent kingdom. Her talents and blandishments were duly appreciated in London society, but she was too fond of political intrigue and agitation to command the full confidence of English statesmen. Castlereagh, Canning, and many of the most eminent men of Great Britain, however, were among her intimate acquaintances. With a view of giving the tzesarevitch (the present emperor Alexander II.) the benefit of the instruction and the society of a lady of Mme. Lieven's vast experience, she and her husband were recalled to St. Petersburg in 1834. The prince was appointed governor of the young Alexander, but his office was almost nominal, and for some time his wife discharged his functions as tutor as efficiently as she had acquitted herself of his duties as ambassador. He however accompanied the tzesarevitch on his travels in southern Europe, while the princess, who had been previously appointed lady in waiting of the empress, remained attached to the Russian court. In 1835 she had the misfortune to lose two of her children, respectively aged 13 and 8. Afflicted VOL. X.-33

by this calamity and yearning for a change, and at the same time for a more independent social atmosphere, she established herself in Paris in 1837, where she took up her residence in the hôtel Talleyrand, the large and beautiful mansion inhabited formerly by that minister, from whom its name is derived. After the death of her husband, which occurred during his visit in Rome, Jan. 10, 1839, she continued to reside in Paris, where her house became a great social focus during the reign of Louis Philippe. She was on peculiar terms of intimacy with M.Guizot, with whom she bad become acquainted in London. She has been often called the Egeria of that statesman; but while the associations which mythological traditions establish between the nymph of that name and the Roman lawgiver Numa were believed to have been matrimonial as well as political, the relations between the adroit Russian princess and the austere French legislator were understood to be based solely upon mutual friendship and strong political sympathies; and the report circulated shortly before her death of their private marriage was not credited. The saloon of the princess of Lieven in Paris was for many years a favorite resort of the chief political, literary, artistic, and social celebrities of that metropolis, and the motley assembly of persons who congregated there included almost all phases of society, from the stately prime minister down to the sprightly comedian. Hence it became one of the fountain heads of the political and fashionable gossip of Paris. Thiers and Molé, the representative of Metternich's policy, Count Apponyi, and the constitutional Spanish statesman Martinez de la Rosa, Lord Granville and Gen. Cass, Lord Lyndhurst and Mr. Bowring, Mme. Thiers and Mme. de Flahaut (the British Baroness Keith), politicians, diplomatists, and ladies of all parties, met at the receptions of the princess; and the principal business of the Russian embassy was done in her boudoirs. With correspondents and acquaintances in every part of Europe, and with her great control over society, she obtained a mass of political and personal information which she forwarded to her friends in Russia. She was on terms of personal friendship with almost every eminent statesman of her time, excepting Lord Palmerston, who distrusted her influence, and of whom she became accordingly an unrelenting enemy. After the revolution of Feb. 24, 1848, she removed to London, but returned to Paris during the presidency of Louis Napoleon, and resumed her receptions in the hôtel Talleyrand, when, beside Guizot and the duke of Noailles and many of the other old attendants upon her reunions, Count Morny, Persigny, Fould, and other notabilities of the new régime, soon united there in social intercourse. Her saloon, however, possessed no longer the cosmopolitan prestige which distinguished it in former times, and was regarded as the headquarters of the Orleans party, although the princess herself professed to keep aloof from all political agitation. After the proclamation

of the empire, she was introduced at the court of Napoleon III., and for some time preceding the Crimean war her saloon became again of great political importance, the princess aiding the Russian ambassador Count Kisseleff in keeping the court of St. Petersburg informed of the progress of events. After the outbreak of the war, however, when Kisseleff and the principal Russian residents of Paris went to Brussels, the princess also spent some time in that city, and was visited there by her faithful friend M. Guizot. In Jan. 1855, she sought and received, under the plea of ill health, permission to return to Paris, where she lived in the utmost retirement until after the restoration of peace in 1856, when her hotel was again thrown open to her numerous friends. Early in Jan. 1857, her health began to fail; but she was in full possession of her mental powers to the last moment. She was a Protestant in faith, and previous to her decease had a long interview with M. Cuvier, a Protestant minister of Paris. Her deathbed was attended by her eldest son Prince Paul, by her nephew Count Benkendorff of Stuttgart, and by M. Guizot. She left a large fortune and a remarkable collection of valuable jewelry.— The princess of Lieven was one of the most active diplomatists of modern times. Her knowledge of history, literature, and languages was extensive; she wrote and spoke the French language with great elegance and facility. Her memoirs would undoubtedly throw light upon many of the diplomatic transactions of the last 50 years; but the announcement which appeared soon after her death, that she bad left them in a state of preparation for publication, seems to have been premature, although it is well known that a great mass of political correspondence and documents is contained among her papers. LIFE INSURANCE. See INSURANCE. LIFE PRESERVER, a contrivance brought into general use within the last 30 or 40 years as a means of preserving persons from drowning. It has been made by act of the U. S. government and of some of the states a necessary article of furniture of steamboats, each boat being required to keep at hand a certain number proportionate to her passenger capacity. Life preservers have been made of various forms and materials, the object in view being to furnish a very buoyant article that can be readily and securely attached to the upper part of the person, or seized and held by those in the water. Pieces of cork have answered this purpose, being conveniently shaped for fitting to the body and provided with cords for attaching them fast. Hollow vessels of wood or tinned iron, made air-tight, and shaped so as to serve on board the vessel as seats, have been much used. In one form the seat is made double, and opening on hinges forms a rectangular float in the centre of which is an aperture sufficient to admit the body of a man, his arms hanging over the sides. Bags of caoutchouc, so made as to be readily filled with air by blowing into them, and shaped for fitting round the neck

or body, have also been largely employed for life preservers; and in other forms they have been made into vests, shirts, and jackets, which, constantly worn on board the vessel, could when occasion required be distended with air, giving great buoyancy to the person wearing them.

LIGHT (Sax. liht, allied to Lat. luz, and Gr. Avky, a shining), a name given, first, to the yet unknown physical agent or cause of the illumination and visibility of bodies in nature; secondly, to the condition of bodies while acted on by such cause; and thirdly, to the sensation arising from the reception of its influence upon the sensitive portion of the eye. Important as is the part which light plays in the physical universe, and familiar as are its manifestations, we can as yet speak with certainty only of its phenomena and their laws. But these very facts have served in all ages to render the subject one of peculiar interest to philosophical minds; and many theories of the nature of light have accordingly been proposed, some of which will presently be named. All natural objects are obviously divisible into two classes: those which originally give forth or emit light, and those which do not. The former are self-luminous, or, as commonly termed, luminous, and are spoken of as sources of light; the latter are commonly said to be non-luminous. Most bodies on which light from a luminous source falls become for the time capable of impressing the retina in the same manner, though not in so intense a degree, as the original source; bodies in this state are said to be illuminated, and in truth they are rendered temporarily luminous. The great and incessant sources of light are the bodies which we now term suns-the centre of our planetary system, and the fixed stars. All solid substances, heat to about 977° F., begin to emit light, and are then said to be incandescent. The light, at first a dark red, becomes successively bright red, yellow, bluish, and white, its brilliancy at from 2000° to 3000° becoming quite insupportable to the eye. Liquids and gases require a higher temperature before incandescence begins. Simple flame is incandescent gas; but the bright flames of illuminating gases, coal, wood, &c., are rendered so by the presence in them of ignited solid particles, usually of carbon. The incandescent or ignited state is produced by heat only; but the cause of the heat may be chemical action, electricity, friction, or compression. Certain minerals, after exposure to the sun, emit light in the dark; wood and some animal substances, as the bodies of fish in certain states of decay, give out light unaccompanied with sensible heat; and many living bodies, as glowworms, similarly emit light; these cases will be treated in the article PHOSPHORESCENCE. A new source has lately been found in the conversion of dark radiations to light, for which see FLUORESCENCE. Thus the direct sources of light may be grouped in 4 classes-suns, incandescence, phosphorescence, and fluorescence; although the third of these includes cases which

are probably quite unlike, and may require a further analysis. The visibility of the sun and stars, and of remote objects on the earth, proves the great distance to which, and freedom with which, either the agent producing light or its effect is transmitted through space. A space or body which offers no obstruction to the passage of such effect, is a free or perfect medium for light; any body which intercepts a portion only of the light, is an imperfect medium. The interplanetary spaces are assumed to be examples of the former, water and glass of the latter; and the latter kind of medium may be either homogeneous throughout its extent, or heterogeneous. That, in a homogeneous medium, the luminous effect is propagated always in straight lines, is a truth derivable from many simple observations, and one which was understood by Euclid and the followers of Plato. The emission of light from a luminous body thus tends to occur in all directions in straight lines, and is termed radiation. The lines of luminous action or effect are what we term rays; so that these are not necessarily distinct and individual objects having the form of needles or straight filaments, as often conceived of, but merely the places of certain lines in space joining a luminous with lighted points. A collection of these lines, parallel, forms a beam of light; of lines separating as they advance, a divergent pencil; approaching as they advance, a convergent pencil. Any highly perfect medium for light is said to be transparent or diaphanous; and the property of such a medium is termed diaphaneity. Bodies through which objects are indistinctly visible are said to be semi-transparent; those through which only a glimmer of light is received, showing the places but not the characters of objects on the further side, translucent; and those through which no perceptible light passes, opaque. Thin plates of clear and well polished glass, or ordinary layers of air, are almost perfectly transparent; but with increase of thickness of any such medium, more light is intercepted, and the transparency of the entire depth lowered. Ground glass, oiled paper, polished horn, and gold leaf are good examples of translucency. As the effect of increased depth of medium, the sun's rays are much less powerful when coming to us from the horizon than when from the meridian. Bouguer has calculated that, at a depth of 700 miles, the atmosphere would become totally opaque to solar light, as water is at a depth of about 700 feet. The conclusion is that absolute transparency and absolute opacity are alike unknown to us; hence that all bodies, at least in certain degrees of tenuity, are media which transmit a portion of the incident light, and intercept another portion. But when rays from a luminous source strike the surface of a body in any degree opaque, and which is not absolutely rough and black, a portion of the incident light, greater or less, is returned from such surface. In proportion as the surface is polished, a larger portion of light, which proceeds back at an angle bearing always a fixed re

lation to that of the incidence, is returned. In proportion as the surface is rough, and at the same time approaches a light color, or white, a larger portion of light is returned in an entirely different manner; in this latter case, every point of the surface impinged upon becomes a centre from which light having the color of the object radiates in all directions, as from a self-luminous body. In proportion as an illuminated body is both light-colored and smooth, at least up to a tolerable degree of polish, it returns more light of both the sorts now named; but though the two kinds of rays are thus in certain directions intermixed, their effects are not so. The light returned at a definite angle, and whose resiliency is due to polish of the arresting surface, always shows in that single direction images of the object from which the incident rays proceeded, and that are perfect in the ratio of the quantity of light thus returning. The light radiated from every point of the illuminated surface, and in all directions, never shows images of its source, but always renders visible the illuminated object itself. The former set of returned rays, moreover, have always the color of the light from the original source; the latter have always the proper color of the illuminated body. Thus, in all respects, these two kinds of returned rays are found, by the observation of the daily phenomena of light, to be radically dif ferent; and this difference Arago and others have experimentally verified. (See COLOR.) It is customary, in most or all treatises and books upon this subject, to say that the two kinds of returned light are thrown back from the illuminated body in essentially the same manner. That portion returned at a definite angle is commonly said to be regularly reflected; that portion which is radiated in all directions is said to be irregularly reflected; the explanation of the difference in the results being that, in the former case, the beams and pencils are returned in their proper relations to each other; in the latter, shivered or splintered by the roughness of the surface on which they had impinged, and scattered in all directions. This explanation is not satisfactory; it is not sufficient to account for the radical difference of the results. Light reflected, upon any supposition or in any manner, must be, after as before reflection, the light of the original luminary or source, must have the colors of that light, and can only show images of the source from which it proceeded. So long as it rebounds from a surface, it can show us no qualities of that surface, but only its own; just as echoed sounds never in themselves convey to us the qualities of the echoing surface, but always those of the original bell, voice, or other source of sound; the surface impinged on, when too much broken, returning nothing at all. But the experiments showing that the light by which illuminated objects are visible is light polarized by refraction, and hence has emerged through the surface of the visible object, instead of being reflected from it, are conclusive. As, of two pianos or viols near each

other, when one is forcibly struck, the accordant strings of the other are thrown into agitation, and so reciprocate or reproduce (not reflect) the original sound; so, when light falls upon any body not so highly polished as to return it all by reflection, or as a mirror (and no bodies do this perfectly), some portion of the light enters among the superficial molecules of the body, is arrested by them, at the same time exciting an agitation among them similar in character to, though less in degree than, that of the original luminary, and the molecules thus agitated become temporarily new centres of radiation, throwing off their own, not reflected light, in all directions. It is only necessary further to suppose that the molecules have by their constitution the ability to respond only to agitations of rays of a certain color or colors. Here, again, we have an exact parallel in sounds; for if, of two instruments containing each a complete octave, all the keys of one were forcibly struck at once, all the keys of the other would together reciprocate (the case of bodies that in sunlight appear white); while, if the second instrument comprised but some portion of an octave, only the keys present could respond (the case of bodies that in sunlight appear colored). All visible objects, then, and to the exact extent of their visibility, are such because they are for the time luminous; the difference being that luminaries proper and incandescent bodies are originally and permanently light-giving during the continuance of certain conditions, while the objects they illuminate are thus rendered secondarily and temporarily luminous. We are now prepared to understand the ways in which light falling on media or bodies is disposed of. 1. In the degree in which the body is both opaque and polished, the impinging rays are caused to rebound, returning at a definite angle; i. e., the light undergoes reflection. 2. In the degree in which, with a polished or otherwise favorable surface, the body is transparent, the rays enter and pass through it (transmission). Under peculiar conditions, this transmitted light is bent from its path (refraction); or decomposed into elementary colors (dispersion); or it becomes endowed with peculiar relations called polarities, in respect to media or surfaces it may afterward impinge on (polarization). For the laws of these several phenomena, see OPTICS, and POLARIZATION. 3. In the degree in which the body is opaque, or its surface is unpolished, or both, the original light enters and disappears within the body; it undergoes extinction. This result, when the light is not reemitted, but lost as such, is commonly termed the absorption of light; but, unless understood as a swallowing up of the luminous energy in the work or effects it can produce, the term is not well chosen. The obvious idea of absorption is that of the action of a porous body in absorbing liquids and gases. But, unlike the case of these latter substances, the light taken in by a dark object does not remain in it as light; all we know is that it disappears within the body-it is extinguished

as light. And yet it is not lost, as no form of energy can be; but in disappearing, it gives place to one of two classes of results. So far as the molecules of the extinguishing body are fitted to reciprocate the energy or agitation it tends to impart to them, they are affected accordingly, becoming new centres of agitation, and of radiation of light, by which the body then becomes visible in all directions; this is secondary luminosity. But so far as, owing to the character of the molecules, or their relation to the colors in the rays they receive, they cannot thus reciprocate and reemit the incident light, this is extinguished as light, and made to reappear in some other form, as that of heat in black and dark bodies, and in other cases, probably, that of electricity, or chemical affinity. Striking confirmations of these views are found in the facts that the most transparent media, as pure glass, become highly opaque and visible by simply grinding and roughening their surfaces; and that no body can be seen of a color that is not in the light falling on it; so that an object that in ordinary lights is of a fiery red, illuminated only by a pure blue light appears black.

As a consequence of the general straight-lined propagation of light, the space on the side of an opaque body opposite to any luminary must be in respect to its rays left in darkness, thus forming a shadow. The term shadow is commonly applied to the darkened spot on any light screen or surface, from which by an intervening opaque body the light has been intercepted. But in truth, such dark spot or figure is always a mere section of the true shadow, and owing to the cutting of the surface showing it in some direction across the axis of the true shadow. The latter, whenever the luminous surface is very small, compared with the size of the intercepting body, is always in effect a frustum of a cone, or regular or irregular pyramidal figure, whose apex is the luminous point, its lesser base a cross section of the opaque body, and its larger base found either on the screen already mentioned, or lost in space. The form of the darkened figure thus cast is of course determined by that of a cross section of the object. When the luminary is larger than the opaque body, the figure in space from which all light of the former will be excluded is conoidal or pyramidal, having its base at the section of the obstructing body, and its apex in space where the rays from opposite sides of the body meet beyond it. When the surface of the luminary is somewhat extended, there will be a belt of space surrounding the complete shadow, from which light from some but not all parts of the luminary will be intercepted. This partially lighted space, when made evident on any screen or surface, is called the penumbra; the middle or darkest portion, the umbra. In the case of the moon's shadow cast on the earth, the partial shadow, being in fact a hollow cone enclosing the complete one, becomes manifest on the earth's surface as a partially lighted ring surrounding one of complete exclusion of the sun's direct rays. (In re