37 



EQUERRIES. 



EQUITES. 



Rees's ' Cyclopaedia,' article EQUATORIAL). The lower part or stand rests 

 on three foot-screws, and needs no description. The upper part is 

 moveable on a cross axis A A, on which it is balanced ; and when the 

 polar axis La set at the proper inclination by the latitude semicircle B, 

 the clamp c retains it there. The polar axis consists of an outer tube, 

 o D, forming one piece with the horizontal axis above-mentioned, and 

 of an interior axis which turns freely within the tube as hi a socket. 

 This latter axis carries the hour circle, T. E, the verniers, F F, bring 

 fixed to the tube. The clamp and tangent screw of the hour-circle 

 are partially seen at Q o. The upper plate H is fixed on the inner axis, 

 and revolves with it. Two pieces, I I, rise from this plate, and carry 

 the collars within which the cross or transit axis, K K, works. The 

 declination circle, L L, and telescope, M M, are fixed to the extremities 

 of the transit axis, the telescope being outside the collar. The decli- 

 nation clamp and tangent screw are seen at x x ; the verniers are on 

 the other side. These are attached to the support which rises from 

 the plate H. Two levels are fixed on the lower part of the stand at 

 o o, but they are only to be used for approximate adjustment. A 

 delicate swing level, r, is hung from the transit axis, and a second 

 level, Q, is fixed to the declination circle. The telescope has a micro- 

 meter, R, carrying wires for measuring small differences of decli- 

 nation. 



It is evident to those who know Fraunhofer's construction, that it is 

 identical with the upper part of this universal equatorial. The sus- 

 pension and motion of the polar axis and hour circle are the same as in 

 the equatorial made by Troughton for the University of Coimbra. The 

 position of the telescope is that of Megnie 1 and Nairne. 



The rules we have already given will enable any one to adjust the 

 universal equatorial ; but if the direction of the meridian be known, 

 it U a simpler plan to adjust the instrument as an altitude and azimuth 

 circle, which it becomes when the polar axis is vertical, and then by 

 inclining the polar axis to the latitude of the place, it becomes an 

 equatorial. There is no provision in the instrument itself for moving 

 the polar axis in azimuth. The whole must be turned bodily, and for 

 this purpose tome preparation should be made in the stand on which 

 the foot-screws rest. 



The following reference* will be useful to the reader. A clock for 

 carrying an equatorial, constructed by Messrs. Troughton and Simms, 

 U described in the ' Abstracts of the Proceedings of the Royal Astro- 

 nomical Society,' vol. iii., No. 6, with a wood-cut. This would pro- 

 bably act somewhat more steadily with a horizontal fly-wheel upon 

 the vertical axis, but its performance is very good. An account 

 of the slipping piece and the wire micrometer to be applied to the 

 equatorial for observing double stars, with directions for their use, 

 in given in the appendix to the ' Companion to the Maps of the 

 Stan published by the Society for the Diffusion of Useful Know- 

 ledge,' 1836. For the mode of using the equatorial as a measur- 

 ing circle, see the ' Cambridge and Greenwich Observations' for 1835 

 and 1836 of Halley'a Comet, of the Solar Eclipse, and of the elonga- 

 tion of Jupiter's fourth Satellite ; and for the corrections for refraction 

 and parallax, the ' Introduction to the Greenwich Observations,' IS 30, 

 to which the reader should look if he wishes to know the best 

 methods of making and reducing astronomical observations in general. 

 Sir Ueorge Shuckburgh's 'Memoir* already referred to contains a 

 valuable history of the instrument, though on consulting the autho- 

 rities, we hare been led occasionally to differ from him. A description 

 of R-uutden a refraction pieee will be found at page 19 of Shuckburgh's 

 paper, along with a collection of tables for computing the effects of 

 refraction and parallax in R.A. and X.I'.D. from the data which this 

 ingenious appendage affords. Pearson's ' Practical Astronomy,' vol. ii. 

 p. 517 ; Littrow, 'Memoirs of the Astronomical Society,' vol. ii. p. 45 ; 

 Kri.-l, ' .Mem. Ast. Society,' vol. iv. p. 495. 



EQUERKIKS (from the French frarie, a stable), the name given to 

 certain officers of the Royal household in the department of the master 

 of the horse, the first of whom is styled chief equerry and clerk- 

 manbal. Their duties fall in rotation. When the sovereign rides 

 abroad in state, an equerry attends. Officers of the same denomina- 

 tion form a part of the established households of the royal dukes, &c. 



EQUIANGULAR, EQUILATERAL, EQUI-CRURAL, EQUI- 

 TAMlKNTIAL, Ac. ftc., a class of words beginning with EQCTI, 

 which, in composition forms an adjective expressive of the equality of 

 two things spoken of. Thus equiangular means having equal angles, 

 and so on. There is a certain liability to confusion, arising from' 

 mistaking between the application of such terms to different parts of 

 the lame figure and to different figures. Thus ' an equilateral triangle ' 

 must mean a triangle which has three sides all equal. But 'two 

 triangles which are equilateral' may mean two triangles in which 

 every side of the first has its equal among those of the second : the 

 two not being separately equilateral. To avoid this, it is sometimes 

 said that two triangles, euch aa have just been mentioned, are 

 mutually equilateral. 



EQUILIBRIUM (ini<ta, Ultra), a state of rest produced by the 

 mutual counteraction of two or more forces. The science of equili- 

 brium is STATICS. 



EQUIMULTIPLES, multiples in which equal numbers of times 

 are token. Thus wren times A and itvcn times B are ejut'-multiples of 

 A and B : a league and a yard are equimultiples of a mile and a foot. 

 The student of the fifth book of Euclid should remember that this 



word has no singular number : 7 A and 7 B are equimultiples, but 7 A 

 is not therefore to be called an equimultiple but one of the equi- 

 multiples. And the same of the word equal, whether separately or in 

 composition : A and B may be equal lines, but A is not equal line. 

 Equality implies comparison of at least two things. 



EQUINOCTIAL, a name given to the equator, from the night 

 being equal to the day when the sun is there. 



EQUINOXES, the intersections of the equator and ecliptic ; the 

 vernal equinox being that in which the sun is when about to rise into 

 the northern hemisphere ; the autumnal equinox being that in which 

 the sun is when about to sink in the southern hemisphere. These 

 terms are relative : for the equinox which is vernal in our hemisphere 

 is autumnal in the southern, and rice versd. 



EQUISE'TIC ACID, Aconitic Add (3HO, C, 2 H 3 ) an acid dis- 

 covered by Braccouot in the eqv.isetwm Jlitviatile, in which it exists 

 combined with magnesia. 



This acid may be obtained in small colourless radiating crystals ; its 

 taste is sharp, and somewhat analogous to that of tartaric acid : it is 

 unalterable in the air. When heated, it decomposes without subliming, 

 and yields an oily uncrystallisable acid product. It dissolves readily 

 both in alcohol and in water : the solution gives no precipitate either 

 with lime or baryta water, but with acetate of lead and protoui- 

 trate of mercury it gives white curdy precipitates : it precipitates the 

 persalts, but not protosalts of iron. 



With potash and soda it yields deliquescent uucrystallisable salts ; 

 with ammonia, a crystallisable salt. With oxide o zinc, with lime, 

 and magnesia, it forms uncrystallisable transparent compounds, which 

 are unalterable in the air. [ACONITIC ACID; CITRIC ACID.] < 



E'QUITES (horsemen), the name of an order in the Roman state. 

 Their origin, according to the old tradition, was this : Romulus having 

 divided his subjects into three tribes, chose from each one hundred 

 young men whom he destined to serve on horseback and act as his 

 body-guard ; this body of cavalry was called the cderes, and afterwards 

 the equites. (Dionys., ii. 13.) Niebuhr supposes (' Hist, of Rome/) 

 that whereas patre* and patricii were titles of honour for individuals, 

 celeres was the name of the whole class as distinguished from the rest 

 of the nation. The three centuries of the celeres were called by the 

 same names as the three tribes of the patricians, namely, Ramues, 

 Titles, and Luceres. Their tribunes are spoken of as a college of 

 priests (Dionys., ii. 64), and it apj>ears that the tribes of the patricians 

 had also tribunes (Dionys., ii. 7). Moreover, when it is said that Tar- 

 quinius Priscus made three new centuries, which he added to the 

 former three, and that the whole went under the name of the Sex Suf- 

 fragia, or the six equestrian centuries, we cannot doubt that the altera- 

 tion which he introduced was a" constitutional and not merely a 

 military one ; that in fact the centuries which he formed were, like the 

 original three, tribes of houses ; that his innovation was nothing but an 

 extension of the political division of the inhabitants of Rome under 

 Romulus. (Niebuhr, " Hist, of Rome.") When Servius Tullius estab- 

 lished the comitia of the centuries, he received the sex suffragia, which 

 included .ill the patricians, into his first class ; and to them he added 

 twelve other equestrian centuries, made up of the richest of the ple- 

 beian order. (Niebuhr.) The ancient writers appear to have laboured 

 under some great confusion with regard to this arrangement. Livy 

 (i. 43) makes a proper distinction between the twelve equestrian cen- 

 turies created by Servius and the six which existed before ; but when 

 he states (L 86) that the cavalry in the reign of Tarquinius Priscus 

 amounted to 1800, he appears to be antedating the origin of the 

 eighteen equestrian centuries which formed part of the constitution of 

 Servius. To the establishment of the comitia centuriata the creation 

 of a body of equites, as a distinct order, seems to be due. The plan of 

 Servius was, to a certain extent, identical with that of Solon. The 

 object of both legislators was to break down the limits to which the 

 old aristocracy was confined, and to set up an order of wealth by the 

 side of the order of birth : not, however, that when a person could 

 produce his 400,000 sesterces, he became ipso facto a knight, as was 

 the case in after times. (Hor. " Ep." i. 1, 57.) According to the 

 Servian constitution, good birth or the sanction of the censors was 

 necessary for gaming a place in the equestrian order. (Polyb., vi. 20 ; 

 Zonaras, vii. 19.) When Cicero says (" De Republica," ii. 2(1) that Tar- 

 quinius established the equestrian order on the same footing as that on 

 which it stood in his own time, and also attributes to the same king the 

 assigning of money to the equites for the purchase and keep of their 

 horses, he is evidently inconsistent. In Tarquin's time, that is, before 

 there was any plebeian order, it was natural euougli that the poorer 

 [wtricians, who were obliged to serve on horseback, just as the 'Ijrinjs 

 at Athens, who were a poorer class than the Pentakosiomedimnoi, 

 (1'lut., " Sol." c. 18.) should be furnished with the means for doing so. 

 But the case was different with the equites after the establishment of 

 an order of wealth. A man might then be of equestrian rank, and 

 yet have no horse assigned to him ; thus, on the one hand, we find at 

 the time of the siege of Veii a number of equites serving on horse- 

 back at their own expense (Liv., v. 7) ; and, on the contrary, L Tar- 

 quitius, who was a patrician, was obliged to serve on foot from his 

 poverty. (Liv., iii. 27.) From this it appears probable that a certain 

 sum was fixed which it was not necessary for every eques to have, but 

 the possessor of which was obliged to serve on horseback at his own 

 expense if no horse could be given him by the public, and that those 



