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of the world. The name of felwort given to G. Amarella, I increase tue general nutrition, without exerting any direct but occasionally applied to the whole genus, is stated by influence upon any other portion of the body than the Dr Prior to be given in allusion to these properties--fel alimentary canal. It is used in dyspepsia, chlorosis, anæmia, meaning gall, and wort a plant. In the same way the and various other diseases, in which the tone of the stomacho Chinese call the G. asclepiaderi, and the Japanese the G. and alimentary canal is deficient, and is sometimes added Buergeri, “ dragon's gall plants,” in common with several to purgative medicines to increase and improve their other very bitter plants whose roots they use in medicine. action. In veterinary medicine it is also used as a tonic, G. campestris is sometimes in Sweden and other northern and enters into a well-known compound called diapente countries a substitue for liops.

as a chief ingredient. By far the most important of the species used in medicine See Sowerby, English Botany, 3d edit., vol. vi. p. 74–81; Hems. is the G. lutea, a large handsome plant 3 or 4 feet high, ley, Handbook of Hardy Trees, Shrubs, and Herbaceous Plants, p. growing in open grassy places on the Alps, Apennines, and 303; Journal of Botany, 1864, p. 65; 1872, p. 166 ; 1878, p. 265; Pyrenees, as well as on some of the mountainous ranges of Pharmacographia, p. 389; Pharmaceutical Journal (1), vol. xii

p. 371; (3) vol. iii. p. 42; (3) vol. vi. p. 90; (3) vol. viii. p. 182; France and Germany, extending as far east as Bosnia and Wood and Bache, United States Dispensatory, 14th edit., p. 438; the Danubian principalities. . It has large oval strongly- Porter Smith, Chinese Materia Medica, p. 102. (E. M. H.) ribbed leaves and dense whorls of conspicuous yellow flowers. GENTILESCHI, ARTEMISIA and ORAZIO DE', painters. Its use in medicine is of very ancient date. Pliny and ORAZIO (1565–1646) is generally named Orazio Lomi de' Dioscorides mention that the plant was noticed by Gentius, Gentileschi; it appears that DeGentileschi was his correct a king of the Illyrians, living 180-167 B.C., from whom the sumame, Lomi being the surname which his mother had name Gentiana is supposed to be derived. During the borne during her first marriage. He was born at Pisa,

, Middle Ages it was much employed in the cure of disease, and studied under his half-brother Aurelio Lomi, whom in and as an ingredient in counter-poisons. In 1552 Tragus course of time he surpassed. He afterwards went to Rome, mentions the use of the root as a means of dilating and was associated with the landscape-painter Agostino wounds.

Tasi, executing the figures for the landscape backgrounds The root, which is the part used in medicine, is tough of this artist in the Palazzo Rospigliosi, and it is said in tho and flexible, scarcely branched, and of a brownish colour great hall of the Quirinal Palace, although by some authoriand spongy texture. It has a pure bitter taste and faint ties the figures in the last-named building are ascribed to distinctivo odour. On account of its porous nature it has Laufranchi. His best works are Saints Cecilia and Valerian, been used in modern surgery, as in the ti of Tragus, as a in the Palazzo Borghese, Rome; David after the death of substitute for sponge tents. The root has been several | Goliath, in the Palazzo Doria, Genoa ; and some works in times analysed with varying results, but Kromayer in 1862 | the royal palace, Turin, noticeable for vivid and uncommon first obtained the bitter principle in a state of purity. This colouring. At an advanced age Gentileschi went to substance, to which the bitterness of the root is due, he England at the invitation of Charles I., and he was em. called gentiopicrin (C20H3,012). It is a neutral glucoside, ployed in the palace at Greenwich. Vandyck included crystallizing in colourless needles, and is contained in the him in his portraits of a hundred illustrious men. His fresh root in the proportion of about itth per cent., but has works generally are strong in shadow and positive in colour. not been obtained in a crystalline state from the dried root. He died in England in 1646. ARTEMISIA (1590–1642), It is soluble in water and spirit of wine, but it does not Orazio's daughter, studied first under Guido, acquired dissolve in ether. It is easily decomposed, dilute mineral much renown for portrait-painting, and considerably excelled acids splitting it up into glucose and gentiogenin, the latter her father's fame. She was a beautiful and elegant woman; being an amorphous yellowish-brown neutral substance. It her likeness, limued by her own hand, is to be seen in is not precipitated by tannin or subacetate of lead. A Hampton Court

. Her most celebrated composition is Judith solution of caustic potash or soda forms with gentiopicrin a and Holofernes, in the Pitti palace; certainly a work of yellow solution, and the tincture of the root to which either singular energy, and giving ample proof of executive faculty, of these alkalies has been added loses its bitterness in a few but repulsive and unwomanly in its physical horror. She days. Gentian root also contains gentianic acid (C14H1003), accompanied her father to England, but did not remain which is inert and tasteless. It forms pale yellow silky there long; the best picture which she produced for Charles crystals, very slightly soluble in water or ether, but soluble I. was David witb the head of Goliath. Artemisia refused in hot strong alcohol and in aqueous alkaline solutions. an offer of marriage from Agostino Tasi, and bestowed her This substance, which is also called gentianin, gentisin, hand on Pier Antonio Schiattesi, continuing however to use and gentisic acid, has been shown by Ville to partake of the her own surname. She settled in Naples, whither she renature of tannin, giving the reactions of that substance turned after her English sojourn ; she lived there in no with ferric chloride, gelatin, and albumen. On this account | little splendour, and there she died in 1642. She had a he proposes to change the name to gentiano-tannic acid. daughter and perhaps other children.

The root also contains 12 to 15 per cent. of an uncrystal- GENTILI, ALBERICO (1552-1608), may fairly be called lizable sugar, of which fact advantage has long been taken the founder of the science of international law. in Switzerland and Bavaria, for the production of a bitter the second son of Matteo Gentili

, a physician of noble family cordial spirit called Enzianbranntwein. The use of this and scientific eminence, and was born 14th January 1552 spirit, especially in Switzerland, has sometimes been followed at Sangincsio, a small town of the march of Ancona which by poisonous symptoms, which have been doubtfully attri- looks down from the slopes of the Apennines upon the disbuted to inherent narcotic properties possessed by some tant Adriatic. After taking the degree of doctor of law at species of gentian, the roots of which may have been indis- the university of Perugia, and holding a judicial office criminately collected with it; but it is quite possible that at Ascoli, he returned to his native city, and was entrusted it may be due to the contamination of the root with that of with the task of recasting its statutes, but, sharing the Veratrum album, a poisonous - plant growing at the same Protestant opinions of his father, shared also his flight to altitude, and having leaves extremely similar in appearance Carniola, where Matteo was appointed physician to the and size to those of G. lutea. Gentian is considered by duchy. The Inquisition condemned the fugitives as contherapeutists to be one of the most efficient of the simple tumacious, and they soon received orders to quit the bitter tonics, that is, of that class of substances which act dominions of Austria. Alberico set out for England, upon the stomach so as to invigorate digestion and thereby travelling by way of Tübingen and Heidelberg, and every

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where meeting with the reception to which his already high His faults are not few. His style is prolix, obscure, and reputation entitled him. He arrived at Oxford in the to the modern reader pedantic enough; but a comparisou autumn of 1580, with a commendatory letter from the earl of his greatest work with what had been written upon tho of Leicester, at that time chancellor of the university, and same subject by, for instance, Belli, or Soto, or even Ayala,

, was shortly afterwards qualified to teach by being admitted will show that he greatly improved upon his predecessors, to the same degree which he had taken at Perugia. His not only by the fulness with which he has worked out lectures on Roman law soon became famous, and the dia- points of detail, but also by clearly separating the law of logues, disputations, and commentaries, which he published war from martial law, and by placing the subject once for henceforth in rapid succession, established his position as all upon a non-theological basis. If, on the other hand, an accomplished civilian, of the older and severer type, and the same work be compared with De Jure Belli et Pacis of secured his appointment in 1587 to the regius professorship Grotius, it is at once evident that the later writer is inof civil law. It was, however, rather by an application of debted to the earlier, not only for a large portion of his the old learning to the new questions suggested by the illustrative erudition, but also for all that is commendable modern relations of states that his labours have produced in the method and arrangement of the treatise. their most lasting result. In 1584 he was consulted by The following is probably a complete list of the writings of Government as to the proper course to be pursued with Gentili, with the places and dates of their first publication :- De Mendoza, the Spanish ambassador, who had been detected Juris intcrpretibus dialogi sex, Lond., 1582 ; Lectionum et episl. in plotting against Elizabeth. He chose the topic to which

quce ad jus civile pertinent libri tres, Lond., 1583-4 : De divers. his attention had thus been directed as a subject for a dis- Lond., 1585; Legal. "comitiorum Oxon. actio, Lond., 1585–6; De

temp. appellationibus, Hanau, 1584 ; De Legationibus libri tres, putation when Leicester and Sir Philip Sidney visited the nascendi tempore disputatio, Witteb., 1586; Disputationum decæs schools at Oxford in the same year; and this was six prima, Loud., 1587; Conulitionum liber singularis, Lond., 1587; months later expanded into a book, the De legationibus libri tertia, 1589 ; De injustitia bellica Romanorum, Oxon., 1590; DO.

De Jure Belli comm. prima, Lond., 1588 ; secunda, ib., 1588-9; tres. In 1588 Alberico selected the law of war as the Arinis Romanis, &c., Hanau, 1599; De ludis scenicis epist. duce, subject of the law dispatations at the annual “ Act" which Middleburg, 1599; De actoribus et de abusu mendacii, Hanau, 1599; took place in July; and in the autumn published in London Lectioncs Virgilianæ, Hanau, 1600 ; De nuptiis libri septem, 1601; the De Jure Belli commentatio prima. A second and a

Ad i Maccab, et de linguaruin mistura, Lond., 1604 ; In tit. si quis third Commentatio followed, and the whole matter, with Math., et de Prof. et Med., Hanau, 1604; De latin. vet. Bibl.,

principi, et ad leg. Jul, maiest., Hanau, 1604 ; In lit. de Malef. et large additions and improvements, appeared at Hanau, in Hanau, 1604; De libro Pyano, Oxon., 1604; Laudes Acad, Perus. 1598, as the De Jure Belli libri tres. It was doubtless in

et Oxon., Hanau, 1605 ; De unione Angliæ et Scotice, Lond., 1605 ; consequence of the reputation gained by these works that Disputationes tres, de libris jur, can., de libris jur. civ.,

de latinitaté Gentili became henceforth more and more engaged in de unione regnorum, de vi civium, Lond., 1605; Hispanicæ ada

ret. vers., Hanan, 1605; Regales disput. tres, de pot. regis absoluta, forensic practice, and resided chiefly in London, leaving his rocationis libri duo, Hanau, 1618; In tit. de verb, signif., Hanau, Oxford work to be partly discharged by a deputy. In 1600 1614; De legatis in teet., Amsterd., 1661. An edition of the Opera he was admitted to be a member of Gray's Inn, and in 1605

Omnia, commenced at Naples in 1770, was cut short by the death was appointed standing counsel to the king of Spain. He . unpublished writings, Gentili complained that four volumes were

of the publisher, Gravier, after the second volume, Of his numerous died 19th June 1608, and was buried, by the side of Dr | lost "pessimo pontificiorum facinore,” meaning probably that they Matteo Gentili, who had followed his son to England, in

were left behind in his flight to Carniola. the churchyard of St Helen's, Bishopsgate. By his wife, Antichità Picene, 1790 ; a Dissertation by W. Reiger annexed to the

Authorities.-Several tracts by the Abate Benigni in Colucci, Hester de Poigni, he left two sons and a daughter. His Program of the Groningen Gymnasium for 1867; an Inaugural notes of the cases in which he was engaged for the Spaniards Lecture delivered in 1874 by T. E. Holland, and the preface were posthumously published in 1613 at Hanau, as His- to a new edition of the Jus Belli, 1877, by the same; works by panicæ advocationis libri duo. This was in accordance with

Valdarnini and Foglietti, 1875; Speranza and De Giorgi, 1876 ; his last wishes ; but his direction that the remainder of his 1878. See also E. Comba, in the Rivista Christiana. 1876–7; and

Fiorini (a translation of the Jus Belli, with essay), 1877; A. Saffi, MSS. should be burnt was not complied with, since fifteen Sir T. Twiss, in the Law Review, 1878.

(T. E. H.) volumes of them found their way, at the beginning of this GENTILLY, a town of France, in the department of the century, from Amsterdam to the Bodleian library.

Seine, is situated on the Bièvre, a short distance south of the The true history of Gentili and of his principal writings fortifications of Paris. Its manufactures include, biscuits, has only been ascertained quite recently, in consequence of soap, vinegar, mustard, wax candles, buttons, leather, and a revived appreciation of the services which he rendered to pottery wares. It possesses a church of the 13th century, international law, The movement to do him honour, a lunatic asylum, a convent, a monastery, and several which originated four or five years sinoe, has in spreading charitablu institutione. The population in 1876 was through Europe encountered two curious cross-currents 10,378. of opinion, --one the ultra-Catholic, which three centuries GENTZ, FRIEDRIC3 Von (1764-1832), born at Breslau, ago ordered his name to be erased from all public docu- May 2, 1764, aptly and accurately described by his disa ments and placed his works in the Index; another the tinguished friend Varnhagen von Ense as a writer-statesnarrowly-Dutch, which is, it seems, needlessly careful of man (Schriftsteller Staatsmann). He was more than 4 the supremacy of Grotius. Preceding writers had dealt publicist or political writer. His position was peculiar, with various international questions, but they dealt with and his career without a parellel. It is believed that no them singly, and with a servile submission to the deci, other instance can be adduced of a man exercising the same sions of the church. It was left to Gentili to grasp as a amount of influence in the conduct of public affairs, without whole the relations of states one to another, to distinguish rank or fortune, without high office, without being a international questions from questions with which they are member of a popular or legislative assembly, without in fact more or less intimately connected, and to attempt their any ostenible means or instrumentality besides his pen. solution by principles entirely independent of the authority Born in the middle class in an aristocratic country, he lived of Rome. He uses, without yielding to them implicit on a footing of social equality with princes and ministers,

. deference, the reasonings of the civil and even the canon the trusted partaker of their counsels and the chosen law, but he proclaims as his real guide the Jus Naturæ, exponent of their policy. the highest common sense of mankind, by which historical His father held an employment in the Prussian civil service; precedents are to be criticized, and, if necessary, set his mother was an Ancillon distantly related to the statesaside

man of that name, On his father's promotion to the mint

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directorship at Berlin and consequent removal to the capital, \ I leave. Berlin with Adam Müller, never to see it again.' he was sent to a gymnasium there, and in due course com- It does not appear that he ever saw his wife again either ; pleted his education at the university of Frankfort-on-the- and his intimacies with other women, mostly of the highest Oder. · He is said to have shown neither liking nor aptitude rank, are puzzling from their multiplicity. He professes for intellectual pursuits till after his attendance on the himself unable to explain the precise history of his settlelectures of Kant at Königsberg, in his twentieth or twenty- ment in Vienna. All he remembers is that he was received first year, when, suddenly lighted up as by inspiration, with signs of jealousy and distrust, and that the emperor, he set to work in right earnest, mastered the Greek and to whom he was presented by Count Colloredo, showed no Latin languages, acquired as perfect a knowledge of French desire to secure his services. Many years were to elapso as could well be attained by one who was not a Frenchman, before the formation of the connexion with Metternich, and a sufficient familiarity with English to enable him the most .prominent feature and crowning point of his to translate from it with clearness and fluency. He also career. managed to gain an intimate acquaintance with English Before entering into any kind of engagements with the commerce and finance, which he afterwards turned to good Austrian Government he applied to the king of Prussia for account. The extent of his acquirements was rendered a formal discharge, which was granted with an assuranco more remarkable by his confirmed habits of dissipation; for that his Majesty, “ in reference to his merits as a writer, from the commencement to the conclusion of his career be coincided in the general approbation which he had so was remarkable for the manner in which, in the midst of the honourably acquired.” A decisive proof of the confidence gravest occupations, he indulged his fondness for female placed in him was his being invited by Count Haugwitz to society and a ruinous passion for play. In 1786 he was the Prússian headquarters shortly before the battle of Jena, appointed private secretary to the royal general directory, and commissioned to draw up the Prussian manifesto and and was soon afterwards promoted to the rank of Kriegsrath the king's letter to Napoleon. It was in noticing this letter (war-councillor). Like Mackintosh, he was fascinated by that Napoleon spoke of the known and avowed writer as the French Revolution at its dawn, and, like Mackintosh, "a wretched scribe named Gentz, one of those men without was converted to a sounder estimate of its then pending bonour who sell themselves for money." In the course of results by Burke. He broke ground in literature in 1794, 1806, he published War between Spain and England, and by a translation of the celebrated Essay on the French Fragments upon the Balance of Power in Europe, on receiv. Revolution, followed in 1794 and 1795 by translations from ing which (at Bombay) Mackintosh wrote :-"I assent to all Ballet du Pan and Mouuier. In 1795 he founded and you say, sympathize with all you feel, and admire equally edited a monthly journal which soon came to an untimely your reason and your eloquence throughout your masterly end. In November 1797 he published a pamphlet under fragment." The bond of union between him and Metterthe title of a Sendscreiben or Missive addressed to Frederick nich was formed in 1840. This was one reason, joined to William III. of Prussia on his accession, pointing out the his general reputation, for his being named first secretary duties of the new sovereign and especially recommending to the congress of Vienna in 1814, where, besides his regular the complete freedom of the press. In the course of the duties, he seems to have made himself useful to several of next three years he contributed to the Historisches Journal the plenipotentiaries, as he notes in his diary that he rea series of crticles “On the Origin and Character of the ceived 22,000 florins in the name of Louis XVIII. fron. War against the French Revolution," with express reference Talleyrand, and £600 from Lord Castlereagh, accompanied to Great Britain. These led to his visiting England, where by "les plus folles promesses." He acted in the same he formed intimate relations with Mackintosh, Lord Gren- capacity at the congress or conference of Paris in 1815, of ville, Pitt, and other eminent men, which proved lasting, Aix in 1818, Karlsbad and Vienna in 1819, Troppau and flattering, and remunerative. The first entries in his pub- Laybach in 1820 and 1821, and Verona in 1822. Tho lished diary, beginning April 14, 1800, and continued (with following entry in his diary for December 14, 1819, has er. breaks) to the end of 1828, rup thus :

posed him to much obloquy as the interested advocate of “On the 14th of April, an agreeable surprise. The Jew elder, reactionary doctrines :-"About eleven, at Prince MetterHirsch, brought me 50 thalers for drawing up I know not what nich's: attended the last and most important sitting of the representation (Vorstellung). May 28.-Received through Baron Krüdener a watch out with (small) brilliants, a present from the commission to settle the 13th article of the Bundes-Akt, and emperor of Russia. June i.-Received through Garlicke a letter had my share in one of the greatest and worthiest results of from Lord Grenville, together with a donation of -£500, the first of the transactions of our time. A day more important than, its kind." The last entry for this year, 1800, is :-"At the end of the year

that of Leipsic.” The 13th article provides that in all states

of the Bund the constitutional government shall be by estates great pecuniary embarrassment. Received £100 from Garlicke and negotiated with Carysfort:”.

instead of by a representative body in a single chamber: “ in The diary for 1801 begins :-" February. --- Very remarkable that allen Bundestaaten wird eine landständische Verfassung on the one side Lord' Carysfort charged me with the translation into : stattfinden.” Remembering what ensued in France.from the French of the English Notes against Prussia, and shortly after wards Count Haugwitz with the translation into Germany of the absorption of the other estates in the Tiers État, it would Prussian Notes against England."

have been strange if Gentz had not supported this 13th Frequently recurring entries of this kind illustrate his article. He was far from a consistent politician, but he was position through life. He was to all intents and purposes always a sound Conservative at heart; and his reputation à mercenary of the pen, but he was so openly and svowedly, rests on his foreign policy, especially on the courage, eloand he was never so much as suspected by those who knew quence, and efficiency with which he made head against the him best of writing contrary to his own convictions at the Napoleonic system till it was struck down. time. This is why he never. lost the esteem or confidunce The most remarkable phase of Gentz's declining years uf his employers;---of Prince Metternich, for example, who, was his passion, in his sixty-seventh year, for Fanny when he was officially attached to the Austrian Government, | Elssler, the celebrated danseuse, which.forms the subject of was kept regularly informed of the sources from which the some very remarkable letters to his attached friend Rahel greater part of his income was derived. Embarrassments (the wife of Varnhagen von Ense) in 1830 and 1831. He of all sorts, ties and temptations from which he was irre. died June 9, 1832. There is no complete •edition of his sistibly impelled to tear himself, led to his change of country; works. The late Baron von Prokesch was engaged in preand an entry for May 1802 runs :-—“On the 15th. I take paring one when the Austrian Government interfered, and leave of my wife, and at three in the morning of the 20th i the design was perforce abandoned

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two thermometers, and a level for deterniiniug the inclina. of surveying extended to large tracts of country, tion of the bar in measuring. The manner of transferring having in view not only the production of a system of maps the end of a bar to the ground is simply this : under the of very great accuracy, but the determination of the curva- end of the bar a stake is driven very firmly into the ture of the surface of the earth, and eventually of the figure ground, carrying on its upper surface a disk, capable of and dimensions of the earth. This last, indeed, may be movement in the direction of the measured line by means the sole object in view, as was the case in the operations

of slot-motion screws. fine mark on this disk is conducted in Peru and in Lapland by the celebrated French brought vertically under the end of the bar by means of a astronomers Bouguer, La Condamine, Maupertuis, Clairaut, theodolite which is planted at a distance of 25 feet from and others; and the measurement of the meridian arc of the stake in a direction perpendicular to the base. Struve France by Mechain and Delambre had for its end the investigates for each base the probable errors of the determination of the true length of the “metre” which measurement arising from each of these seven causes:was to be the legal standard of length of France.

alignment, inclination, comparisous with standards, read The basis of every extensive survey is an accurate tri- ings of index, personal errors, uncertainties of temperature, angulation, and the operations of geodesy consist in—the and the probable errors of adopted rates of expansion. measurement, by theodolites, of the angles of the triangles; The apparatus used in the United States Coast Survey the measurement of one or more sides of these triangles on consists of two nieasuring bars, each 6 metres in length, the ground; the determination by astronomical observations supported on two massive tripod stands placed at vlie of the azimuth of the whole network of triangles ; the de- quarter length from each end, and provided, as in Colby's termination of the actual position of the same on the sur-apparatus, with the necessary mechanism for longitudinal, face of the earth by observations, first for latitude at some transverse, and vertical adjustment. Each measuring rod of the stations, and secondly for longitude.

is a compensating combination of an iron aud a brass bar, To determine by actual measurement on the ground the supported parallel to one another and firmly connected at length of a side of one of the triangles, wherefrom to infer one end, the medium of connexion between the free ends the lengths of all the other sides in the triangulation, is not being a lever of compensation so adjusted as to indicate a the least difficult operation of a trigonometrical survey. constant length independent of temperature or changes of When the problem is stated thus-To determine the num- temperature. The bars are protected from external influber of times that a certain standard or unit of length is ences by double tubes of tinned sheet iron, within which contained between two finely marked points on the surface they are movable on rollers by a screw movement which of the earth at a distance of some miles asunder, so that allows of contacts being made within noooo of an inch. the error of the result may be pronounced to lie between The abutting piece acts upon the contact lever which is certain very narrow limits,-then the question demands very attached to the fixed end of the compound bar, and carries serious consideration. The representation of the unit of a very sensitive level, the horizontal position of which delength by means of the distance between two fine lines on fines the length of the bar. It is impossible here to give the surface of a bar of metal at a certain temperature is a full description of this complicated apparatus, and we never itself free from uncertainty and probable error, owing must refer for details to the account given in full in the te the difficulty of knowing at any moment the precise United States Coast Survey Report for 1854. This appatemperature of the bar; and the transference of this unit, ratus is doubtless a very perfect one, and the manipulation or a multiple of it, to a measuring bar, will be affected not of it must offer great facilities, for it appears to be possible, only with errors of observation, but with errors arising from under favourable circumstances, to measure a mile in one uncertainty of temperature of both bars. If the measuring day, 1:06 mile having been measured on one occasion in bar bo not self-compensating for temperature, its expansion eight and a half hours.

,

In order to test to the utmost the must be determined by very careful experiments. The apparatus, the base at Atlanta, Georgia, was measured thermometers required for this purpose must be very care- twice in winter and once in summer 1872-73, at temperafully studied, and their errors of division and index error tures 51°, 45°, 90° F.; the difference of the first and second determined.

measurements was +0:30 in., of the second and third The base apparatus of Bessel and that of Colby have been +0.34 in.,—the actual length and computed prubable error described in FIGURE OF THE EARTH (vol. vii. p. 598). The expressed in metres being 9338.4763 + 0.0166. It is to average probable error of a single measurement of a base be noted that in the account of a base recently measured in line by the Colby apparatus is, according to the very elab- the United States Lake Survey, some doubt is expressed as orate investigations of Colonel Walker, C.B., R.E., the Sur- to the perfection of the particular apparatus of this de. veyor-General of India, +1.5x (u meaning "one millionth"). scription there used, on account of a liability to permanent

” W. Struve gives = 0·8u as the probable error of a base changes of length. line measured with his apparatus, being the mean of the The last base line measured in India with Colby's comprobable errors of seven bases measured by him in Russia ; pensation apparatus bad a length of 8912 feet only, and in but this estimate is probably too small. Struve's appa- consequence of some doubts which had arisen as to the ratus is simple : there are four wrought iron bars, each two accuracy of this compensation apparatus, the measurement toises (rather more than 13 feet) long; one end of was repeated four times, the operations being conducted in each bar is terminated in a small steel cylinder presenting such a manner as to indicate as far as possible the actual a slightly convex surface for contact, the other end carries magnitudes of the probable errors to which such measures a contact lever rigidly connected with the bar. The shorter are liable. The direction of the line (which is at Cape arm of the lever terminates below in a polished hemisphere, Comorin) is north and south, and in two of the measurethe upper and longer arm traversing a vertical divided arc. ments the brass component was to the west, in the other In measuring, the plane end of one bar is brought into two it was to the east. The differences between the indi contact with the short arm of the contact lever (pushed vidual measurements and the mean of the four aro forward by a weak spring) of the next bar. Each bor has +:0017, - .0049, - .0015, + :0045 in feet. The measure

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ments occupied from seven to ten days each,--the average be natural objecte presenting themselves in suitable posirate of such work in India being about a mile in five days. tions, such as church towers; or they may be ohjects

lebih The method of M. Porro, adopted in Spain, and by the specially constructed in stone or wood on mountain tops French in Algiers, is essentially different from those or other prominent ground. In every case it is necessary just described. The measuring rod, for there is only that the precise centre of the station be marked by some one, is a thermorietric combination of two bars, one of permanent mark. In India no expense is spared in making platinum and one of brass, in length 4 metres, furnished permanent the principal trigonometrical stations-costly with three levels and four thermometers. Suppose A, towers in masonry being erected. It is essential that every B, C three micrometer microscopes very firmly sup trigonometrical station shall present a fine object for obported at intervals of 4 metres with their axes vertical, servation from surrounding stations. and aligned in the plane of the base line by means of a

Horizontal Angles. transit instrument, their micrometer screws being in the line of measurement. The measuring bar is brought In placing the theodolite over a station to be observed under say A and B, and those micrometers read; the bar from, the first point to be attended to is that it shall rest is then shifted and brought under B and C. By repetition upon a perfectly solid foundation. The method of obtainof this process, the reading of a micrometer indicatiug the ing this desideratum must depend entirely on the nature of end of each position of the bar, the measurement is made. the ground; the instrument must if possible be supported The probable error of the central base of Madridejos, which on rock, or if that be impossible a solid foundation must has a length of 14664.500 metres, is estimated at = 0.17d. be obtained by digging. When the theodolite is required This is the longest base line in Spain ; there are seven to be raised above the surface of the ground in order to others, six of which are under 2500 metres in length; of command particular points, it is necessary to build two scafthese one is in Majorca, another in Minorca, and a third in folds,--the outer one to carry the observatory, the inner one Ivica. The last base just measured in the province of Bar- to carry the instrument,—and these two edifices must have celona has a length of 2483.5381 metres according to the no point of contact. Many cases of high scaffolding have first measurement, and 2483.5383 according to the second. occurred on the English Ordnance Survey, as for instance

The total number of base lines measured in Europe up at Thaxted Church, where the tower, 80 feet high, is surto the present time is about eighty, fifteen of which do not mounted by a spire of 90 feet. The scaffold for the obexceed in length 2500 metros, or about a mile and a half, servatory was carried from the base to the top of the spire ; and two-one in France, the other in Bavaria-exceed that for the instrument was raised from a point of the spire 19,000 metres. The question has been frequently discussed 140 feet above the ground, having its bearing upon timbers whether or not the advantage of a long base is sufficiently passing through the spire at that height. Thus the instrugreat to warrant the expenditure of time that it requires, ment; at a height of 178 feet above the ground, was or whether as much prerisìon is not obtainable in the end insulated, and not affected by the action of the wind on the by careful triangulation from a short base. But the answer observatory. cannot be given generally ; it must depend on the circum- At every station it is necessary to examine and correct stances of each particular case.

the adjustments of the theodolite, which are these:the line It is necessary that the altitude above the level of the of collimation of the telescope must be perpendicular to its sea of every part of a base line be ascertained by spirit axis of rotation ; this axis perpendicular to the vertical levelling, in order that the measured length may be reduced axis of the instrument; and the latter perpendicular to the to what it would have been had the measurement been . plane of the horizon. The micrometer microscopes must made on the surface of the sea, produced in imagination. also measure correct quantities on the divided circle or Thus if I be the length of a measuring bar, h its height circles. The method of observing is this. Let A, B, C.... at any given position in the measurement, the radius of be the stations to be observed taken in order of azimuth ; the earth, then the length radially projected on to the level the telescope is first directed to A and the cross-hairs of the

h of the sea is 1 1. In the Salisbury Plain base line the telescope made to bisect the object presented by A, then l. In the Salisbury Plain base line the the microscopes or verniers of the horizontal circle (also

of reduction to the level of the sea is – 0.6294 feet.

the vertical circle if necessary) are read and recorded. The In working away from a base line ab, stations c, d, e, f telescope is then turned to B, which is observed in the same are carefully selected so as to obtain from well-shaped tri- manner; then C and the other stations. Coming round by angles gradually increasing sides.

continuous motion to A, it is again observed, and the agreeBefore, however, finally leaving

ment of this second reading with the first is some test of the base line it is usual to verify it

the stability of the instrument. In taking this rouad of by triangulation thus: during the

angles-or “arc," as it is called on the Ordnance Surveymeasurement two or more points,

it is desirable that the interval of time between the first as P, 9 (fig. 1), are marked in the

and second observations of A should be as small as may be base iu positions such that the

consistent with due care. Before taking the next arc the lengths of the different segments

horizontal circle is moved through 20° or 30°; thus a dif of the line are known; then,

ferent set of divisions of the circle is used in each arc, which taking suitable external stations,

tends to eliminate the errors of division. as h, k, the angles of the triangles

It is very desirable that all arcs at a station should bhp, phq, hqk, kqa are measured.

contain one point in common, to which all angular measureFrom these angles can be com.

ments are thus referred,—the observations on each arc computed 'the ratios of the seg

mencing and ending with this point, which is on the Ordments, which must agree, if all

nance Survey called the “referring object.” It is usual for operations are correctly per

this purpose to select, from among the points which have formed, with the ratios resulting

to be observed, that one which affords the best object for from the measures. *Leaving the

precise observation. For mountain tops a." referring ob. buse line, the sides increase up

Fig. 1.

ject” is constructed of two rectangular plates of metal in t» ten, thirty, or fifty miles, occasionally, but seldom, reach the same vertical plane, their edges parallel and placed at ing a hundred miles. The triangulation points may either such a distance apart that the light of the sky seen through

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