CHRONOLOGY.

CHRONOLOGY, n. kró-něľ'o-ji [Gr. chronos, time or duration; logos, discourse: F. chronologie]: the science that treats of the dates of past events and arranges them in order; the method of measuring or computing time. CHRONOLOGICAL, a, krón ō-liji-kal, or CHRONOLOG IC, a. -ik, relating to chronology; containing an account of past events in the order of time. CHRONOLOG'ICALLY, ad. li. CHRONOLOGIST, n. krō-nõľ'ò-jist, or CHRONOL'OGER, n. jer, one who endeavors to discover the true dates of past events, and to arrange them in order; one who is versed in chronology.

CHRONOLOGY: science of the divisions of time, and of the assignment of dates of past events. It has two main branches-mathematical C. and historical C. Mathematical C. is engaged with such of the units for the measurement of time as begin and end with the period of complete evolution of recurring celestial phenomena: see CALENDAR: YEAR: MONTH: DAY: and CYCLE. Historical C. uses these units among others to measure the distance in point of time between events, and to fix their dates. As in geography and navigation, longitude is measured from some arbitrary line such as the meridian through Greenwich, so in historical C., dates are fixed by giving their distance from some arbitrary point of time, chosen usually because of some remarkable occurrence which signalized it. Such a fixed point, or epoch, forms the beginning of an era, though in common usage these two words are not always exactly discriminated. It is thus that dates have been aptly said to be to events in history what the latitude and longitude of places are to the places in geography and navigation. The mathematical, or, to speak more properly, the astronomical units of time above referred to have not been the only units used in historical C. In early times the more accurate methods of mathematics were unknown, and such vague periods as 'a generation,' or the lifetime of leading persons in a nation, such as the priestesses of Juno, or of the kings, were assumed as units in historical C. The great variety of eras, too, in ancient times confuses the student. Thus the era of the Greeks began with the year of the first olympiad, or that in which Corobus was victor; being the first celebration of the games at which the victor's name was recorded, and which is calculated to correspond to the year B.C. 776. From this epoch, the Greeks measured time by olympiads or periods of four years. Thus, the 3d year of the 12th olympiad would be B.C. 729. The Roman era was reckoned from the founding of the city, being either B.C. 752 or 753. The Roman practice of dating events from the building of the city, seems the first instance of the method of reckoning time from a fixed point by single years, and thus forms one of the great stages in chronology. The Mohammedan era commences with the flight of Mohammed, A.D. 622, called the Hedjrah (q.v.). The Roman and Greek methods of measuring time continued in use long after the birth of Christ; the olympiads, indeed, appear to have been employed in Europe till the 304th olympiad, or A.D. 440.

CHRONOLOGY.

From A.D. 312, however, the public mode of computation throughout the Roman empire was by indictions, which were periods of 15 years, beginning with 312 (see INDICTION); and this mode was at one time almost universally followed in the west, and in France, was not altogether discontinued till the end of the 15th c. The Christian era or era of the Incarnation, is said to have been first proposed A.D. 527, and is now universally used in Christendom, and even by some non-Christian nations. Part of the business of C. is to determine the relationships of the different eras, so as to enable one to express, in the language appropriate to one mode of computation, the date of an event recorded in another. Owing to the birth of Christ being a comparatively recent event, the Christian era is attended by the inconvenience of counting backward from it for the dates of occurrences prior to it. To obviate this, various comprehensive periods, such as the Julian and Louisian periods have been invented, applicable to most events within the limits of history.

Various systems of C., such as the Chinese, Babylonian, Egyptian, Indian, and Chaldæan, are worthy of attention. For accounts of the periods which these nations respectively assign to their histories, see CHINESE EMPIRE: BABYLON: etc. Of Sacred C. there have been various systems. In these the epochs are the creation of the world, and the flood; but the chief copies of the Old Testament do not agree as to the dates of these events. While the Hebrew text reckons 4,000 years from the creation to the birth of Christ, and to the flood 1,656 years, the Samaritan makes the former much longer, though it counts from the creation to the flood only 1,307 years. The Septuagint version differs from both. It removes the creation of the world to 6,000 years before Christ, and 2,250 years before the flood. In the lack of historic data these differences are impossible of reconciliation. The Bible makes no attempt at a scientific C. any more than at a scientific treatment of other departments of human inquiry. It is now, however, universally admitted, that the creation of the world is not to be regarded as having occurred even so recently as B.C. 6,000. The modern and doubtless the most reasonable understanding of the first chapter of Genesis leaves the period of the creation quite indefinite, and one modern scheme of interpretation stretches out the days of creation into periods of indefinite length. The Newtonian C. was an attempt, now generally admitted to have been unsuccessful, to rectify the obvious blunders of ancient chronologers, by determining certain epochs by means partly of astronomical calculations, and partly of itical examination of such chronicles as measured time by reigns and generations. By a very fine argument, the soundness of which has since been found questionable, Newton set down the date of the Argonautic expedition as being 43 years after the death of Solomon. or B.C. 937.

The computation of time by divisions or periods, so as to fix dates by bringing them into relation with each other, seems to have been practically unknown till B.C 8th cen

CHRONOMETER.

tury. In the earlier ages no records were made, and wher they began to exist they perished through neglect, accident, or the religious or patriotic bigotry of discoverers and conquerors. Thus the nrst annals of Greeks, Etruscans, and Romans are lost; the traditions of the Druids were neither written nor long remembered; Chi-Hoang-Ti is said to have burned the Chinese books about B.C. 220; and the Spaniards destroyed the Mexican picture-writings. There can be no C. without epochs from which to start, and epochs were long local or at best national. The Greeks, after Timæus, Bbout B.C. 350, reckoned from that olympiad in which Corcbus won at the olympic games, B.C. 776; the Babylonians from the era of Nabonassar, B.C. 747; and the Romans from the foundation of their city, variously placed from B.C. 747 to 753; the latter date, given by Varro, is now agreed on. Des Vignoles collected over 200 estimates as to the creation, which vary from B.C. 3483 to 6984; yet an Indian era places it at B C. 3102. Abp. Usher's computation, B.C. 4004, though highly arbitrary, has been gererally accepted, and agreement is everything here. The chronologic efforts of Berosus, Manetho, Eratosthenes, and Apellodorus (B.C. 3d and 2d c.) were well-intentioned rather than successful, for their works survive only in fragments. In computing from any epoch, the month and day (if known) must be considered as well as the year; e.g., the olympiads were counted from July 1, and American copyrights were long dated in such a year of the independence of the United States,' reckoning from 1776, July 4 An approxi mate list of eras, epochs, or periods, with their dates of commencement as known or supposed. is here subjoined:

CHRONOMETER, n. krů-năm è-tér [Gr. chronos, time; metron, a measure] · any instrument or machine that measures time, as a clock or a dial; usually a large watch,

CHRONOSCOPE-CHRYSALIS.

fitted with a compensating balance-wheel, and various precautions against irregularity, and constructed with great nicety, for use at sea see WATCH: HOROLOGY. CHRONOMETRIC, a. krůn'õ-měť'rik, or CHRONOMETRICAL, & -rrkal, pertaining to. CHRONOMETRY, n. krů-něm ě-tri, the art of measuring time, or of constructing chronometers.

CHRONOSCOPE, krón' o skōp: instrument contrived by Bir Charles Wheatstone to measure the duration of certain short-lived luminous phenomena, such as the electric spark, of which the eye itself can be no judge, owing to the persistence of impressions of light on the eye after the cause of sensation has ceased. The phenomenon is observed by! reflection in a mirror, in such rapid motion that the image of the luminous object would appear to describe a circle, supposing the luminosity to endure long enough. Should the phenomenon be instantaneous, the image will appear as a mere point; should it last for an appreciable time, the image will form an arc, greater or less, of the circle. The electric spark is found by this test to have no duration.

CHROOLEPOID, a. kri-čľ'ě-poyd [Gr. chrõõs, the skin; lepida, a scale; eidos, resemblance]: in bot., made up of small yellow scales. CHROOLEPUS, n. krō-ŏl'ě-pus, a curious genus of algae found on damp walls, etc., having orange tints when fresh.

CHRUDIM, chro dim: town of Bohemia, beautifully situated on a small river, about 62 m. s.e. of Prague. It is walled, has a noble collegiate church, a high school and Capuchin convent, manufactures of cloth, and very important horse-markets. Pop. (1880) 11,886; (1890) 12,128.

CHRYSALIS, n. kris'ă-lis,or CHRYS'ALID, n. [L. chrysalis -from Gr. chrusallis, the gold-colored sheaths of butterflies

a

d

Chrysalises.

a, Orange-tip Butterfly; b, Black-veined White Butterfly; c, Swallow. tailed Butterfly; d. Purple Emperor: e, Silver-washed Fritillary: f, Duke of Burgundy Fritillary.

-from chrusus, gold] the dormant stage which caterpillars

CHRYSANTHEMUM.

pass through before emerging into the winged state, as butterflies, moths, etc., strictly belonging to those pupa of butterdies which are adorned with golden spots, but extended to the pups of lepidopterous insects generally, and even of other orders of insects. The chrysalids of lepidopterous insects are inclosed in a somewhat horny membranous case; sometimes very angular, sometimes nearly round; generally pointed at the abdominal end, sometimes at both ends; and before the caterpillar undergoes its transformation into this state it often spins for itself a silken cocoon, with which earth and other foreign substances are sometimes nixed, so as to increase its size, and within which the chrysalid is concealed. Chrysalids are often suspended by cords, and generally remain nearly at rest; some have. the power of burying themselves in the earth; others are. bound by a single silken thread which passes round their middle (see cut); some twirl themselves round when touched, or when the stalk or leaf to which they are suspended is touched; and in general, they give signs of life, when disturbed, by violent contortions of the abdominal part: see INSECTS: PUPA: LEPIDOPTERA: BUTTERFLY HAWK-MOTH: MOTH: SILKWORM. CHRYS'ALID, a. lid, pertaining to a chrysalis.

CHRYSANTHEMUM, n. kri-san' the mum [Gr. chrusos, gold; anth mon, a flower]: genus of plants of the nat. ord. Composite, sub-ord. Corymbifere; having a hemispherical or nearly flat involucre, with imbricated scales, membranous at the margin, a naked receptacle, the florets of the disk tubular and hermaphrodite,

those of the ray strap-shaped and female, the fruit destitute of pappus. The species of this genus are annuals, perennials, or shrubby; and all have leafy stems. They are natives chiefly of the temperate parts of the old world. C. leucanthemum, the Ox-EYE, or Ox-EYE DAISY, is abundant in fields, meadows, and grassy places of woods, in most parts of Europe. It has large flowers, with white ray and yellow disk. It is often a troublesome weed among hay and in pastures; being perennial, and having a creeping brittle rootstock, it is not easily extirpated. CORN MARIGOLD, frequent weed in cornfields, an annual, with large, deep yellow flowers. It is dealt with like annual weeds in general, by pulling it when young. -C. carinatum, an annual species with white ray and dark-red disk, the scales of the involucre keeled, native of Barbary, is frequently cultivated in green-houses or

Chrysanthemum.

where climate permits-in flower-gardens. The favorite