the idea of attack and turned toward Wytheville, near which he arrived on the afternoon of the 10th and encountered Col. John H. Morgan, who had followed him from Saltville and by a detour first gained the town with a brigade and two battalions. A detachment of Morgan's command had been pushed out to a small gap in the mountain, through which alone Averell could approach the town from the road on which he was marching. The detachment was immediately attacked and Morgan marched to its assistance with all his command, and Averell fell back to a commanding ridge' 800 yards from the gap. The contest continued four hours, or until nightfall, in a succession of attacks on the one side and retreats on the other, when Morgan fell back a short distance and Averell withdrew and next morning marched for Dublin, where he arrived in the evening and, resuming his march, joined Crook at Union on the 15th. Averell had 114 killed and wounded, and lost nearly 100 in prisoners. Morgan had 50 or 60 killed and wounded. When Gen. Stoneman made his raid into southwestern Virginia in December 1864 he captured Wytheville on the 16th, partially burned it, and next day sent a detachment to destroy the lead mines, which was done without loss. On Stoneman's second raid in southwest Virginia and western North Carolina in March 1865, Col. J. K. Miller, with 500 picked men of his cavalry brigade, captured Wytheville 6 April and destroyed the

depot of supplies at that point and the bridges over Reedy Creek and at Max Meadows. At Wytheville Miller was attacked by Confederate infantry and cavalry, but after hard fighting repulsed them, and withdrew with a loss of 35 killed, wounded, and missing, and rejoined the main column on its march for Salisbury, N. C. E. A. CARMAN.

Wyttenbach, vit'ten-baн, Daniel, Dutch scholar: b. Bern, Switzerland, 7 Aug. 1746; d. sgeest, Holland, 17 Jan. 1820. He studied at Marburg, Göttingen, and Leyden; became professor of Greek at the Remonstrant Gymnasium at Amsterdam in 1771, of philosophy at the Athenæum in 1779, and succeeded in 1799 to Ruhnken's chair of rhetoric at Leyden. His greatest work is the edition of Plutarch's Morals, with copious annotations and an admirable 'Greek Index to Plutarch's Works' (17951830). He retired in 1816, and died after some years of blindness. His 'Opuscula appeared in 1820. Consult Mahne, Via D. Wyttenbach' (1823).

Wyttenbach, Johanna Gallien, Dutch writer: d. Leyden. She was married to D. Wyttenbach (q.v.) when he was 72, and after her husband's death lived at Paris and was given the degree of doctor in philosophy by Marburg, in 1827. Among her writings were: Theagenes (1815); Leontes' Banquet' (1812); and the romance 'Alexis' (1823).

X

the twenty-fourth letter and nineteenth consonant of the English alphabet: it is a superfluous letter since it stands for no sound that cannot be signified by other letters. When it occurs in the beginning of a word it is always pronounced in English as z: Xenophon, zenophon, xiphoid, ziphoid; in the middle of a word it is usually equal to ks: axis, aksis, Saxon, sakson; but when in a word it ends a syllable, more especially an initial syllable, if the syllable following it is open or accented, the r has often the value of gz, as in luxury, lugzury, exhaust, egzhaust. Final r is always equal to ks. As an initial letter r does not occur in English save in words mostly technical and derived from Greek, and in a few words, mostly proper names, of Spanish origin. -The power of x in English, as in Latin, is that of the Greek letter ri (E), but its form is that appropriated in the Greek alphabet to the guttural aspirate chi (X,x), Before the introduction of r (§) the Greeks represented the sound of x by X2, xs, and the Latins at first did the like, writing Maxsumus, proxsumus; but as x had in their writing no function but that of representing, with s the sound of Greek ri, the very sight of the r, even before the eye came to the s, raised in the mind the idea of a sibilant, and thus rendered the sibilant letter itself superfluous, and before long it was omitted and x, standing alone, represented the two characters x and s. In the popular pronunciation of Latin in the later period of the empire, r seems to have been sounded like s or ss: some inscriptions of that period have visit for vixit and milex for miles: this change in the sound-value of has persisted in the modern language of Italy in which ss or s is regularly substituted for the Latin : saxum becomes sasso, experimentum, esperimento, maximus, massimo, and so on. And in French, in words derived from Latin, ther occurring in the middle of a word is often changed to ss: laxare becomes laisser; or Latin r is changed to the sound of sh: vexare becomes facher; and the word soixante is pronounced soissante. X hardly occurs in German words of native origin; its sound is usually represented in that language by chs, examples: ochs (ox), wachs (wax), Sachse (a Saxon).

X-Rays, or Röntgen Rays, a form of radiant energy originating in the highly-exhausted vacuum tubes of Crookes (see VACUUM), and resembling light in certain respects, though differing from it notably in many ways. The X-rays are propagated in straight lines, and are capable of affecting the sensitive plates that are employed in photography, so that

subsequent development will cause the affected portions to blacken, just as though the plate had been subjected to the action of light. The X-rays are practically invisible to the eye. They are capable, however, of exciting brilliant fluorescence in certain minerals, and their presence may, by this means, be made distinctly evident_to the eye. The X-rays were discovered in 1895 by Professor Wilhelm Konrad Röntgen, of the University of Würzburg; the name being given by him to signify that the ultimate nature of the radiation was unknown, "X" being a letter that is commonly used in algebraic operations to represent an unknown quantity.

In the nearly-perfect vacuums employed by Crookes, the high-tension electrical discharge does not take place between the electrodes in the form of a spark, but, when the tension of the gas in the tube is sufficiently low, it assumes the form of a luminous streamer, proceeding across the tube from the negative electrode (or "cathode"), in a direction perpendicular to the surface of this electrode. The luminous shaft that proceeds outward from the cathode in this manner is called the "cathode ray," and it exhibits many interesting phenomena. (See VACUUM.) In a general way, it may be said to deport itself as though it were composed of a storm of tiny electrified projectiles, which are negatively charged by contact with the cathode, and are then violently repelled from the cathode in a direction perpendicular to its surface. Many experimenters have devoted their attention to the cathode ray, in the endeavor to discover its true nature; and among these experimenters was Lenard, a young German physicist, who was assistant to Dr. Heinrich Hertz, at Bonn, at the time of the latter's death in 1894. Lenard appears to have been impressed with the idea that it is possible to make the cathode ray emerge from the vacuum tube, into the air. It would seem that the projectile explanation offered above precludes any such possibility; but Lenard found that if the vacuum tube is provided with a very thin pane of aluminum foil at the place where the cathode ray strikes it, this ray can apparently pass through the aluminum so as to emerge into the air outside of the tube. In Lenard's apparatus the vacuum tube is entirely enclosed by opaque material, so that the light from the interior of the tube may not affect the eye; the thin pane of aluminum being placed, as indicated above, at the place where the cathode ray within the tube strikes the wall of the tube. When the proper precautions are taken against the escape of any ordinary light from the interior of the tube, the cathode ray, in a darkened room, can be seen to emerge from the tube through the

aluminum, taking the form of a divergent and diffuse luminous brush, which, as Lenard showed, can be deflected by a magnet. Lenard also found that the emerging brush affects a photographic plate, and he investigated the relative transparencies (or opacities) of various substances for it. Röntgen repeated certain of the experiments of Crookes, Hittorff, Lenard, and others, and made the further discovery that vacuum tubes also generate another kind of radiant energy, which he called "X-rays," and which resemble the cathode ray in some respects, but differ from it in not being deflected by a magnet, and in not being distinctly visible to the eye. The X-rays and the cathode ray are both capable of exciting strong fluorescence in certain crystalline substances which are subjected to their influence; and in working with the X-rays it is customary to make use of fluorescent screens, which are coated with barium platinocyanide, or with calcium tungstate, or with some other substance in which the fluorescent effects of the X-rays are very pronounced. A screen of this kind, when exposed to the action of the X-rays, becomes luminous, and the intensity of the luminosity is proportional to the intensity of the radiation striking the screen. Thus when a screen of this kind is glowing with uniform brilliance, and an object (such as a piece of lead or glass) which is more or less opaque to the rays is interposed between the screen and the tube from which the X-rays proceed, the object so interposed shields the screen, over a certain area, from the exciting X-rays, so that a comparatively dark region is produced, as though the opaque object were casting a shadow. The relative opacities of various substances cah be studied in this manner, by merely interposing the objects whose opacities are to be tested, and noting the depths of the apparent shadows that are produced. Glass is found to be much less transparent to the X-rays than an equal thickness of aluminum or of wood, and, in general, it may be said that the opacity of any substance is approximately proportional to the density of the substance. When a portion of the human body is interposed between the tube and the fluorescent screen, the bones, having a greater density than the flesh that surrounds them, cast shadows upon the screen, so that their images can be seen, dark, against a much lighter background. In comparatively thin parts of the anatomy, such as the hand, very good shadowgraphs can thus be had of the bones; but when the X-rays have to traverse thicker parts of the body, such as the chest, the shadowgraphs are far less distinct. The ribs can be seen through the entire body, though somewhat imperfectly, and the liver and heart can also be indistinctly perceived. Tumors and other morbid growths can likewise be traced to some extent, as well as tubercular areas in the lungs, and certain other pathological conditions. (The haziness of the images that are obtained when the X-rays traverse thick tissues is due, no doubt, to "secondary radiation," as explained below.) Owing to the great density of lead, bullets that are embedded in the flesh can frequently be located with considerable accuracy, and in the surgical treatment of bullet wounds the X-rays are therefore often highly useful.

Permanent images of the shadowgraphs that are produced by the X-rays can easily be had by substituting a sensitive photographic plate for

the fluorescent screen referred to above; the image being allowed to fall upon the photographic plate, which is afterwards developed in the usual manner.

There has been some controversy about the origin of the X-rays; - that is, about the part of the tube from which they emanate. Röntgen believed that they originate in the region where the cathode ray is stopped by the wall of the tube, or by some other obstacle; and although this view has been disputed by other experimenters, it is now believed to be correct. That is, when the cathode ray strikes against the glass wall of the containing tube, the X-rays appear to originate at this point on the wall; and when the tube is so constructed that the cathode ray strikes directly against the anode, then the X-rays proceed from the anode. It has been found, indeed, that the radiation is much more intense when the design of the tube is such as to cause the cathode ray to impinge directly upon the anode, and in most of the modern tubes for the production of X-rays this construction is adopted. It is observed that when an X-ray tube has been operated for a considerable time, the vacuum within it becomes more and more perfect, so that it is eventually difficult to force through the tube a discharge sufficient to generate the rays with the desired intensity. Moreover, the penetrative character of the X-rays given off by a tube appears to depend to a considerable extent upon the degree of perfection of the vacuum, as was observed by Röntgen himself. For these reasons, most of the X-ray tubes are made, at the present time, with regulable vacuums, the main tube being provided with a side bulb, with which it communicates by means of a tube. The glass walls of the auxiliary bulb become covered with a thin layer of condensed air (see ADSORPTION); and when, through the operation of the apparatus, the vacuum in the main tube has become so highly perfected that the discharge passes with difficulty, the walls of the auxiliary bulb are warmed by a gas flame or otherwise, so that a portion of the air that is held condensed upon them is driven off into the interior of the bulb, and thence into the main tube, until the vacuum becomes reduced sufficiently to permit of the satisfactory passage of the discharge.

The experimental investigation of the X-rays is beset with serious difficulties, because these rays possess properties so different from those of ordinary light that few of the methods that are employed for the study of light can be applied to them. For example, the X-rays cannot be refracted, and they are apparently not capable of regular reflection. Hence they cannot be focused in any way. Furthermore, they cannot be made to exhibit diffraction, interference, or polarization. Many of the methods employed in the study of light are based upon one or more of these phenomena; and hence, the phenomena themselves being absent in the case of the X-rays, little or no help in the investigation of this form of radiation can be had from our previous experience with light.

When the X-rays traverse a solid which is more or less transparent to them, the distinctness of the shadow-like images that are seen upon the fluorescent screen, or which are recorded upon the photographic plate, diminishes with the thickness of the object through which the rays pass. The images become diffuse with

increasing thickness in such a way as to suggest that the X-rays do not really travel in straight lines, but that they are capable of bending about an obstacle so as to influence the screen, or the sensitive plate, behind the obstacle. A more careful study of the phenomenon indicates, however, that the diffuseness of the image under these circumstances is due to the fact that each particle in the course of the X-rays acts as a centre of "secondary radiation," from which X-rays again emanate, though with reduced intensity, in all directions. The passage of X-rays through a body may therefore be compared with the passage of ordinary light through a light mist, each particle of the mist acting, in a similar manner, partly as a mere obstacle, and partly as a new centre of radiation, so that the shadows that are observed in such a case are diffuse and indefinite. The discovery of the X-rays led to much speculation among physicists as to their ultimate physical nature. In the theory of light it was long ago pointed out that the disturbance which takes place in the ether when a light-wave travels through that medium must be such that the displacements that occur, whatever their nature may be, occur only in directions that are perpendicular to the direction in which the ray itself progresses. (See ETHER; UNDULATORY THEORY.) There appeared to be no phenomenon whose existence corresponded to the existence of a wave of compression and rarefaction in the ether, such as occurs in air when a soundwave passes; and in order to explain the absence of this longitudinal wave of rarefaction and compression it was necessary, in the elastic-solid theory of light, to assume that the ether is absolutely incompressible, or to make certain other special assumptions with respect to its nature. Upon the discovery of the X-rays, it was therefore natural to inquire if they do not constitute the missing phenomenon corresponding to a compressive disturbance in the ether. This idea, although it was an attractive one, and agreed well with the absence of polarization in the X-rays, gradually fell out of favor, giving way temporarily to the hypothesis that the X-rays are similar in nature to ordinary light, but that they are of exceedingly short wave-lengthmuch shorter, in fact, than any form of radiation previously known. There was much to be said in favor of this latter hypothesis, for it was known that the phenomena that would be manifested by light of wave-lengths exceedingly short in comparison with the average distances between the molecules of transparent bodies would be very different from those that are observed in connection with light of longer wave-lengths. Even if the wave-length of the X-rays were very short, however, it would be natural to expect that interference phenomena of some sort might still be observable; and yet no such phenomena could be detected. What is probably the true explanation of the nature of the X-rays was given almost simultaneously by Stokes, Lehmann, and J. J. Thomson. The "pulsation theory advanced by these physicists assumes that the X-rays do not, like light, consist of trains of waves, in which a series of similar waves follow one another in rapid succession and at regular intervals, but that they consist, instead, of a series of electrical pulsations through the ether, following one another without any regularity. A mathematical analysis of the conse

quences of this theory indicates that it is in entire harmony with the observed absence of refraction, reflection, polarization, interference, and diffraction. The cathode ray within the vacuum tube is believed to consist of a storm of tiny molecular fragments, or electrons (q.v.), the velocities of which may be as great as 40,000 miles per second. When one of these charged particles comes in contact with a solid wall or other obstacle, the abrupt change that is produced in its motion causes a violent alteration in the electrical stress that exists in the ether immediately about the point of collision, and the result is, that this point of collision serves as a centre from which a pulsation of electrical disturbance radiates outward. A fresh pulsation will therefore be produced every time a charged electron collides with the solid obstacle, and hence, since there is no regularity in the collisions, there will also be no regularity in the resulting ethereal pulsations. This view of the nature of the X-rays accords with all the known phenomena, even with the demonstrated absence of the X-rays from ordinary sunlight. This last fact was tested and verified by experiments upon Pike's Peak where a sensitive photographic plate was exposed for several months to the action of the sunlight, protected by wrappings that were impervious to light, but which would transmit, freely, any X-rays that might happen to be present. The elevated position was selected in order that any absorptive action that the earth's atmosphere might exert upon the rays should be reduced to the smallest practicable amount. Subsequent development of the exposed plate showed no evidence of the action of X-rays upon it.

In the course of experiments with the X-rays, it was soon found that they are capable of producing more or less marked physiological effects. The most noticeable of these consists in the "burning" of the skin, the cuticle becoming reddened and inflamed under protracted exposure to these rays, much as it does upon exposure to strong sunlight. It was also found that the human eye can perceive the X-rays faintly, though it is believed that the retina is not directly affected by them; the sensation of a faint, indefinite light to which they give rise being probably due to the fluorescing of some of the inner parts of the eye under their influence. The known fact that the artificial culture of tuberculosis germs must be conducted in the dark, and that strong sunlight will check the development of such germs, or destroy them altogether, led to the hope that the X-rays might have similar properties, and that on account of their marked power of penetrating the human flesh, they might be useful in the treatment of tuberculous disease. These hopes were not very fully rewarded, but the X-rays have nevertheless proved valuable in the treatment of superficial tuberculosis (lupus) and cancer. Some authorities still hold that the cases of apparent cancer which have been successfully treated by the X-rays have not been correctly diagnosed, and that true carcinoma does not yield permanently to the action of this agency. See ETHER; ELECTRON; LIGHT; RADIOACTIVITY; VACUUM. Con

sult, also, Barker, Röntgen Rays,' in the Scientific Memoir Series,' where several of the most important of the papers that have appeared A. D. RISTEEN, PH.D., Editorial Staff, 'Encyclopedia Americana.

are collected.

X. Y. Z. Correspondence, in United States history, the name given to the despatches of the three commissioners to France in 1797-8, Marshall, Pinckney, and Gerry. These commissioners reached Paris in October 1797, but were refused recognition by the Directory. They were, however, notified by the secretary of the Marquis de Talleyrand, minister for foreign affairs, that agents would be sent to conclude negotiations. The first of these, Hottinguer, stated that a "loan" of $1,200,000 would be the necessary means of placating the Directory: the other two, Bellamy and Hauteval, urged that in case the American government would buy at par stock amounting to 32,000,000 livres, but whose market-value was really about one half that amount, the transaction would be viewed as a loan. The intimation was that in default of money war would ensue. These terms were promptly rejected. The despatches sent by the commissioners were submitted in copy to Congress, X., Y., and Z., having been substituted for the respective names of the French agents. A great stir was caused at the time. Preparations for hostilities were made, and war on the sea actually broke out. Consult for the text of the correspondence American State Papers, Foreign Relations,' Vol. II. (1832).

Xanthian (zăn'thi-an) Marbles, a large collection of marbles of various ages (from 545 B.C. onward) discovered near Xanthus, in 1838.

Xanthine, an organic base, C.H.N.O2, occurring in small amounts in many animal secretions, in the blood, urine, liver, in some urinary calculi, and in tea extract. It may be readily made by the action of nitrous acid on guanine. A white amorphous powder slightly soluble in water, and forming crystalline compounds with both acids and bases. It is closely related to theobromine and caffeine, the alkaloids found in cocoa and coffee respectively. Caffeine may be considered as xanthine in which three hydrogen atoms have been replaced by three methyl (CH3) groups.

Xanthippe, zăn-thip'e, the wife of Socrates, the Greek philosopher. Her shrewish temper has become proverbial, but many of the stories about her are probably false, for in ancient Athens gossip was cultivated to the perfection of a fine art, the point and not the truth of the story being the chief consideration. Xanthippe's natural inequalities of temper were heightened by the peculiarities of her spouse, especially his indifference to the commonplace duty laid on the head of the house to make both ends meet. The philosopher received her reproaches with such good-humored indifference that it is not surprising she sometimes resorted to other weapons beside her tongue; as on the occasion when she is said to have finished up a tirade by sousing the philosopher, though his remark, as he moved dripping from the scene, that when Xanthippe thundered she watered, must have shown her that here, too, she was powerless.

Xanthippus, zăn-thĭp'us, Spartan general. He assisted the Carthaginians in the first Punic war and defeated the Romans under Regulus at Tunes (now Tunis) 255 B.C.

Xanthos, zăn'thos, the mythical horse of the mythical hero, Achilles. It is related in the Iliad that being chided by his master for

leaving Patrocles on the field of battle, the horse turned his head reproachfully, and told Achilles that he also would soon be numbered with the dead, not from any fault of his horse, but by the decree of inexorable destiny. He

He wrote a

Xanthos of Lydia, Greek historian. flourished about the 6th century B.C., and was work called 'Lydiaca, a history of Lydia oncontemporary with Herodotus. ward from heroic times, giving also a geographical description of the country. Only fragments of it have been preserved.

Xanthox'ylum, a genus of the Rutacea, composed of erect or climbing shrubs, or trees, often with prickly branches. The leaves are compound, pinnate, sometimes reduced to three, or rarely, to one, leaflet, usually pellucid dotted. The flowers are small, in axillary or terminal panicles, and are from 3- to 5-merous. The fruits split in two, with one or two shining black seeds. Xanthoxylum is a large genus, found both in the Eastern and Western hemispheres, especially in their warmer parts. The species are so aromatic and pungent that in the countries where they exist they are popularly called peppers, specially X. piperitum, called Japan pepper, which is regarded as an antidote for poison. an X. rhetsa, Indian species, has small yellow flowers and small round berries, which, when unripe, taste like the skin of a fresh orange. Its fruit, and the seeds and bark of X. alatum, which grows near the base of the Himalayas, and those of X. budrunga, also Indian, are given as aromatic tonics in fever, diarrhoea, dysentery, and cholera. They are used as a condiment in India and as a fish-poison. The small branches are employed to make walking-sticks, and the twigs as toothbrushes. The seeds of the latter are as fragrant as lemon peel; X. clava and X. fraxineum applied externally to the gums or taken internally, are powerful sudorifics and diaphoretics used in toothache, paralysis of the muscles of the mouth, and rheumatism. The root of X. nitidum is sudorific, emmenagogue, etc. powdered bark of X. hiemale is given in Brazil in earache; and the capsules and seeds of X. hastile are employed in northern India to intoxicate fish. The West Indian species of Xanthoxylum are called yellow-wood, X. caribæum being differentiated as the prickly yellow-wood. is a tree, 20 to 50 feet high, whose prickly young stems are made into walking-sticks. The wood X. is used for inlaying and for furniture. cribsosum is the satin-wood of Florida and the West Indies, which when first cut has the odor of the veritable satin-wood X. fagara (Pterota) is a small tree common in the same region, and tropical America, producing a hard, heavy, reddish-brown wood known as savin or iron-wood in the West Indies, or as the wild-lime. Still another species is X. emarginatum, a shrub with coriaceous foliage, exported under the name of rose-wood, but is called licca-tree or lignumvorum at home. The commonest species of the X. Americanum, a shrub or small tree, with northern United States, and the hardiest, is the odd-pinnate leaves, and twigs which are generally prickly. The cymose flowers are axillary and sessile, without calyx, and they are greenishwhite. The capsules are black and ellipsoidal. It is called prickly-ash or toothache-tree, because both Indians and country people used the

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