09 



ARCOGRAPH. 



ARCTU'RUS. 



10 



arid superfluous enactments to keep, aa it were, the statute-book in a 

 pure and consistent state. (Dem. 'contra Lacr.' p. 940, 10, and 12 

 ' contra Zenoth.' p. 890, 10 ; Lys. ' contra Andoc.' p. 104, 15 ; Herod 

 6, 109, 111 ; Lys. 'contra Pane.' p. 166, 32, and 40.) It appears that 

 the whole college of archons was sometimes assembled in council (Dem 

 ' contra Meid.' p. 542, 2) ; but we have no information respecting the 

 authority which they collectively exercised. 



For further information on the various and important duties assignee 

 to the different archons, in addition to this brief and general notice, the 

 reader is referred to the authorities mentioned above ; but we woulc 

 remind the young student, in his inquiries, that the reliance to be 

 placed on the accuracy of even a credible and well-informed author 

 must depend in some measure on the circumstances under which his 

 information is given ; and this should especially be kept in mind when 

 as in the subject of the present article, all our information, so far as il 

 is supplied by the Greek classics, is obtained, not from regular essays 

 but from incidental notices. Our meaning in this caution will be besl 

 explained by an instance. The subject of inquiry may be the manner 

 in which certain officers were appointed ; and this, as in the case of the 

 archons, may have varied at different times. The mode of appointmeni 

 may, according to a common practice with the Athenians, be implied 

 by an epithet familiarly joined with the title of the office. Now, it is 

 possible that an author, who when writing professedly on the subject 

 would have given minutely accurate information, may use this epithet, 

 familiar to him, inaccurately with reference to the times of which he i 

 speaking, if the circumstance indicated by it is of no importance to th 

 subject immediately before him. Evidence drawn from a casual expres- 

 sion must often be taken into account, but then it should be carefully 

 rated at its proper value. 

 ARCOGRAPH. [CYCLOOBAPH.] 

 ARCTIC CIRCLE. The term arctic is derived from the Greek, and 

 signifies literally of or belonging to the bear, meaning the constellation of 

 that name. Arctic circle had formerly a different signification from 

 that which it now has. Among the Greeks it meant the parallel to the 

 equator which just touches the horizon, being entirely above it, and 

 which therefore separates those parallels which are always above, from 

 those which are partly above and partly below, the horizon. (See Strabo, 

 Casaub. p. 95.) Similarly the antarctic circle (if the phrase were used) 

 would be a parallel to the equator which touches the horizon, being 

 entirely below it, and which therefore separates those parallels which 

 never rise above, from those which are partly below and partly above, 

 the horizon. Thus every different latitude had a different arctic 

 circle ; and in the latitude in which astronomy was first cultivated, the 

 great bear just swept the sea, and did not set, whence the boundary 

 circle obtained its name. 



In the modern sense of the term, it is one fixed circle, or very nearly 

 o ; and the first use of it as such is found in the celebrated treatise on 

 the sphere, by Holywood, better known by the name of Sacrobosco, 

 published in the twelfth century. For the complete meaning of the 

 term, we refer to DAT. We can only here briefly remind the reader 

 that at the equator all days are equal ; that in going northwards from 

 the equator, the day of the summer solstice lengthens as the latitude 

 increases, until we reach the pole, where there is but one day and 

 night in the year, of six months each. There must therefore be some 

 circle of the globe, in the northern hemisphere, at which the longest or 

 Rummer solstice day is just twenty-four hours ; and an opposite circle 

 in the southern hemisphere, at which the sun does not appear for 

 twenty-four hours. The first is the arctie, the second the antarctic, 

 circle of the earth. We need hardly say, that at the day of the winter 

 solstice in the northern hemisphere, there is a 

 day of twenty- four hours in length at the antarctic 

 circle. 



P and p (fy. 2.) are the north and south poles 

 of the earth, the lines through which serve to 

 , remind us of the earth's axis. A B is the equator, 

 and p H and o L are the directions in which the 

 sun is seen at the northern summer and winter 

 solstices, that is, the line which points to the sun 

 rises and falls between n o and o L twice in a 

 year. We do not consider the apparent motion 

 of the sun round the earth, because, as the sun is 

 always on the meridian of some place, and any conclusion respecting 

 day and night drawn from one meridian holds good for any other, we 

 may conceive the meridian P np A to move round with the sun. Or, to 

 consider it in another point of view, instead of supposing the sun to 

 appear to move round, let it remain in the fixed meridian, pBp\, and 

 increase the daily rotation of the earth by a quantity equal to the daily 

 motion of the sun on the equator, which will preserve the relative 

 'iis, leaving us only to take notice of the rise and fall of the sun 

 in the ecliptic ; which is the cause of the peculiar phenomena of the 

 arctic circle. The semicircle o v, in the first figure, is supposed to be 

 cut out and applied to the right hand figure, o to o, in such manner 

 that the needle, v, shall always be directly opposite to the sun. In the 

 figure (2.) are given the extreme positions of o v ; namely, M n m, at the 

 northern summer, N w n, at the northern winter, solstice. The semi- 

 circle o v covers all those parts of the earth which do not see the sun, 

 and the rotation round the axis, tp, brings every part of the earth 

 under o v when its night begins. N and mn are the arctic and ant- 



Fig. 1. 



arctic circles. By cutting out a semicircle equal to o v, and placing it 



**, 



in different positions on the second figure, the following will appear, on 

 a little consideration : 



1. At the summer solstice (when v is at v) all circles above M N will 

 be in light for twenty-four hours, and all below m n in darkness : and 

 vice rend at the winter solstice. 



2. At the equinoxes (v is at A) every circle-will be in light for twelve 

 hours, and the same time in darkness. 



3. During the passage from the eqninox- to the summer solstice 

 (v moves from A to n), at every moment some circle above M N emerges 

 entirely into light, and an opposite circle below m n begins to be entirely 

 covered by darkness : and both states remain until the return of the 

 circle ov in the next quarter of the. year. And vice vend for the 

 passage from the equinox to the winter solstice (when v moves from A 

 to w). 



4. No circle lying between M N and m, n is ever entirely in light or 

 entirely in darkness. 



Hence, to find the duration of light at any place above the arctic 

 circle, that is, to find during what part of the year the sun performs 

 his daily rotation entirely above the horizon, look in an almanac for 

 the times before and after the summer solstice, at which the declination 

 of the sun is equal to the polar distance (or latitude subtracted from 

 K> ) of the place. Between those two times there is perpetual light. 

 For example, the north point of Nova Zembla (latitude 75, polar 

 distance 15) will have perpetual light between May 1 and August 12, 

 1859. For the time of perpetual darkness do the same with the winter 

 solstice : thus there will be perpetual darkness at the above-mentioned 

 place from November 3, 1859, to February 9, 1860. 



The north polar distance of the arctic circle is equal to the angle 

 HOB, the greatest declination of the sun, or the OBLIQUITY of the 

 ecliptic. The south polar distance of the antarctic circle is the same. 

 This quantity changes very slightly from year to year. It is as follows : 



January 1, 1858, 23 27' 28"'29 

 January 1, 1859, 23 27' 27"'84 



decreasing at present by about half a second yearly. 



The arctic and antarctic circles are the boundaries which separate 

 the frigid from the temperate zones, as they are called. The part of 

 the earth included within each of the two is about 4^ per cent, of the 

 whole surface of the globe. The best known points through or near 

 which the arctic circle passes are Cape North in Iceland, the Maelstrom 

 whirlpool, the mouth of the Oby, Behriug's Straits, and the south of 

 Melville Island. For discoveries of land within the antarctic circle see 

 ANTARCTIC OCEAN, in GEOO. Div. of ENU. CYC. 



The arctic and antarctic circles of the heavens occupy positions with 

 respect to the celestial poles similar to those occupied by the same 

 circles on the earth. Thus a traveller going round the arctic circle 

 vould always have some point of the celestial arctic circle directly over 

 head, or in his zenith. But the term is hardly ever employed by 

 astronomers. 



In all that precedes we have taken no notice of REFRACTION, the 

 effect of which is to raise the sun a little towards the nearest pole at 

 every point of the globe, thus lengthening the day and diminishing the 

 night. In some latitudes the effect would be very considerable, and 

 would increase the duration of light by as much as a day 

 ARCTURIN. [ARBUTIN.] 



ARCTU'RUS, or a Boptis, a star of the first magnitude in the con- 

 itellation Bootes. It derives its name from two Greek words, signifying 

 rhe tail of the bear, and, though not in the latter constellation, it is 

 'ery nearly in a right line drawn through the two hinder stars of the 

 ail ({ and TJ). It rises N.E. by E. at Greenwich, and is on the meridian 

 n about 7J hours after rising ; which takes place at half-past seven A.M. 

 in the 1st of January, and about two hours later for the first of every 

 ucceeding month. Its mean places are as follows : 



Jan. 1, 1859 

 Jan. 1, 1860 



Right Ascension. 

 . 14 h 9 13-8 1 

 . 14 9 16-6 



Declination. 

 19 55' 5-5" 

 19 54 46-6 



ts animal increase of right ascension is 2''8 ; its annual decrease of 

 leclination is 18"'9. This is not all owing to precession and nutation, 

 as the star has a proper motion (or change of place relatively to sur- 



