4--i6 



PERILLUS PERIOD. 



in the orbit of a planet, or comet, which is nearest 

 to the sun ; being the extremity of its transverse 

 axis, nearest to that nx-us in which the sun is placed, 

 anil thus opposed to the aphelion, which is the op- 

 extremity of the same axis. The ancient 

 astronomers used, instead of this, the term periga'tim, 

 as they placed the earth in the centre. The perihe- 

 lion distances of the several planets, the mean dis- 

 tance of the earlh from the sun being taken as unity, 

 are as follows : 



Mercury, .1815831 Ceres, 2.fi800flfiO 



Vi-nu., " .T1(U7!O Pallag, '2.5.'?5!08() 



Knrth. .9831468 Jupiter, 5.1546127 



Mnr-, 1.4305.95 Saturn, 9.48-ifiO 



VwtaL iflVMQQ Uranus, 19.1369347 



Juno, 2.41. "-'l!H 



SIT Aphelion and Equation. 

 1M.IULLUS. See Phalaris. 

 PERIMETER, in geometry ; the bounds or limits 

 of any figure or body. The perimeters of surfaces 

 or figures are lines ; those of bodies sire surfaces. In 

 circular figures, instead of perimeter, we say circum- 

 ference, or periphery. 



PERIOD (from the Greek ripeta, a circuit) ; a 

 division of time, or of events occurring in it. The 

 astronomer calls the time of a revolution of a heaven- 

 ly body, or the time occupied in its return to the 

 same point of its orbit, its period. See Planets, and 

 Kepler. 



In chronology, period denotes a division of time, 

 during which certain phenomena complete their 

 courses, which are repeated in never-ending succes- 

 sion. Chronology depends entirely upon astronomy; 

 and before the latter had made known the true mo- 

 tions of the heavenly bodies, the former remained in 

 a confused state. The principal periods of the Greeks 

 were Melon's lunar period of nineteen years, or 

 6940 days, according to which the Greeks computed 

 their astronomical calendar from 432 B. C.j the 

 period of Calippus (330 B. C.), or that of Alexander, 

 which comprised four times nineteen, or seventy-six 

 years minus one day ; and the still more accurate 

 period of Hipparchus, of 304 years, which made the 

 tropical solar year only six minutes and sixteen se- 

 conds too long. The Roman induction (q. v.) was a 

 period of fifteen years, the origin of which is not 

 very clear. The Julian period, invented by Scali- 

 ger, consisting of 7980 Julian years, was intended 

 to reduce to the same result the different computa- 

 tions of the year of the birth of Christ from the 

 creation. It is the product of the numbers twenty- 

 eight, nineteen, and fifteen ; or the solar, lunar, and 

 indiction cycle. (See Cycle.) After twenty-eight 

 times nineteen, or 532 years, the new and full moons 

 return in the same order, upon the same day of the 

 week and month, in the Julian calendar, and the 

 three chronological cycles (the solar cycle of twenty- 

 eight years, the lunar cycle of nineteen years, and 

 the indiction cycle of fifteen years) recommence at 

 the same time. This period is also called the great 

 Paschal cycle, and the Victorian or Dionysian period. 

 The year of the birth of Christ, in the Julian period, 

 is 4714. It is now little used, as we reckon by 

 years before and after Christ. 



In history, a period is a certain division of time, 

 determined by events, giving to it the character of 

 a whole. A judicious division of history into periods 

 is very necessary for a clear view of the whole, and, 

 in fact, is the necessary result of an intelligent 

 method of studying history. The ancients wrote 

 general history ethnographically and chronologically, 

 or in the way of annuls. Bossuet, in iiis Discours 

 tur I' Hiftoire universelle, and Offerhaus, in his Com- 

 pendium Historice universalis, divided history by 

 centuries, and by subdivisions of the latter; but 

 modem historians have preferred to divide universal 



history by periods. Voltaire, in his Essaisur I' Hif- 

 toire generate, Millot, Condillac, Gatterer, Schlozer, 

 and, in general, all the principal modern historians, 

 have followed this plan. The progress of civiliza- 

 tion and ot civil liberty is more important than the 

 order of dynasties, or the fluctuations of power; and 

 the periods of history ought to be founded upon the 

 various stages or manifestations of these. A judicious 

 division into periods can be effected only by a clear 

 and philosophical view of history. Philosophical 

 views are the great object of the study ; but incau- 

 tious philosophizing often leads the reader to deduc- 

 tions drawn from his own imagination rather than 

 from a rigid scrutiny of facts. The division of 

 history into periods, founded on general views, re- 

 quires, therefore, great care. The philosophico-his- 

 torical school of Germany, at the head of which, at 

 present, we may put professor Hegel, has fallen into 

 glaring errors in this respect. This same censure, 

 however, by no means belongs to all the philosophi- 

 cal historians of that country, but should be confined 

 to the school which is particularly termed philoso- 

 phical. The division into periods must vary, both 

 according to the chief aim of the historian and ac- 

 cording to the amount of historical knowledge exist- 

 ing in his time. Thus an historian who proposes to 

 write a history of religions, or who thinks that re- 

 ligious revolutions have always been the most im- 

 portant, and are the best standards by which to 

 measure the other changes in human society, will 

 establish his division into periods accordingly. Ano- 

 ther will take, as his basis, the political changes of 

 nations. The most perfect division would be that 

 which should adopt, as the basis of each period, that 

 feature which was the most strongly chfinicteristic 

 of it, which is not always easy, as one principle often 

 continues strongly operative, while another has risen 

 to an important influence, threatening to supersede 

 it. In such a division of universal history, civiliza- 

 tion, religion, government, learning, important in- 

 ventions, &c., would all become, in turn, the bases 

 of the various periods. See Epochs, and History. 



A period, or sentence, in writing, is a series of 

 logically connected passages ; a passage developed 

 in properly connected parts. Aristotle's definition, 

 which makes it a discourse having its beginning and 

 end in itself, is indistinct. Every passage would 

 then be a period ; and, on the other hand, a whole 

 speech, a whole work, would be a period. Periods 

 should not be too long, but it is impossible to fix the 

 limits distinctly. Cicero's rule, that a period ought 

 not to be longer than four hexameters, is as insuffi- 

 cient as the other, that it should be sufficiently short 

 to be spoken at one breath, without exhaustion of 

 the lungs. If it is properly constructed, the voice 

 finds resting-places enough ; and if its parts are 

 logically connected, it is not difficult to follow their 

 connexion, and to form a distinct conception of the 

 whole. In some languages, the rules for the con- 

 struction of periods are stricter than in others ; some 

 allow great liberty. To the former belongs the 

 English language ; to the latter, the Greek, Latin, 

 and German. The genius of the German language, 

 in particular, allows of very long and involved 

 periods, in which perspicuity frequently suffers seri- 

 ously ; and it often happens that the whole mean- 

 ing of a long sentence in that language depends upon 

 the last word, so that we are kept in suspense as to 

 the ideas conveyed, until the decisive word appears. 

 The following rules should be observed in the con- 

 struction of a period : 1. The chief idea must be 

 made prominent, whilst the secondary ideas are pre- 

 sented with a force proportioned to their importance; 

 2. there should be a certain proportion between 

 the length of the different members ; 3. the sub- 



