EARL MARSHAL OF ENGLAND. 



EARTH, MEAN DENSITY OF THE. 



7*1 



,.: ;. ., 



read of the subordinate or iubjct titles. This 

 riou* names in almost vnrj country in Km,.|><-. 



By th English H U called earl, a nun* derived to us from the ealder- 

 man of the Anglo-Saxon* and the eorle of the Danes. By the French 

 it is called rvmtt ; by the Spaniarda eonde ; and by the Germans yraf, 

 under which generic title are included eereral distinct degrees of rank, 

 landgravos, or count* of provinces ; palagnves, or counts palatine, of 

 which there are two aorU ; markgravea, or count* of marches, or fron- 

 tiers (whence ma^AL^ or marquess) ; burghgraves, or counts of citiee ; 

 counts of the empire; oounta of territories ; and several others. [Cor NT; 

 BABOM.] 



After the battle of Hastings, William the Conqueror recompensed 

 his follower* with granta of the lands of the Saxon nobles who had 

 fallen in the battle, to be held of himself as strict feuds ; and having 

 annexed the feudal title of earl to the counties of the Saxon earls (with 

 whom the title was only official), he granted them to his princijxil 

 captains. 



These earldoms were of three kinds, all of which were by tenure. 

 The first and highest was where the dignity was annexed to the seisin 

 or possession of a whole county, with jura regalia. In this caw the 

 county became a county palatine, or principality, and the person 

 created earl of it acquired royal jurisdiction and seigniory. In short, 

 a county palatine was a perfect feudal kingdom in itself, but held of a 

 superior lord. The counties of Chester, Pembroke, Hexham, and Lan- 

 caster, and the bishopric of Durham, have, at different times, been 

 made counties palatine ; but it does not appear that the title of earl 

 palatine was given to the moat ancient and distinguished of them 

 namely, the earl of Cheater before the time of Henry II., surnamed 

 Fitz- Empress, when the title of palatine was probably introduced from 

 the empire. The earls of Chester created barons and held parliaments, 

 and had their justiciaries, chancellors, and barons of their exchequer. 

 This county palatine reverted to the crown in the reign of Henry III. 

 The second kind of earls were those whom the king created earls of a 

 county, with civil and criminal jurisdiction, with a grant of the third 

 part of the profits of the connty court, but without giving them actual 

 aeiain of the county. The third kind was where the king erected a 

 large tract of land into a county, and granted it with civil and criminal 

 jurisdiction to be held per ten-ilium uniat comitattlt. 



I'mler the early Norman kings, all earls, as well as barons, held 

 their titles by the tenure of their counties and baronies; and the 

 grant, or even purchase, with the licence of the sovereign of an earl- 

 dom or a barony, would confer the title on the grantee or purchaser ; 

 liut with the solitary exception of the earldom of Arundel, earldoms 

 by tenure have long since disappeared, and in late times the title has 

 been conferred by letters patent under the great seal. Earls have now 

 no local jurisdiction, power, or revenue, as a consequence of their title, 

 which is no longer confined to the names of counties or even of places ; 

 for several earls, as Earl Spencer, Earl Qrey, and others, have chosen 

 their own names instead of local titles. 



The coronet of an English earl is of gold surmounted with pearls, 

 which are placed at the extremity of raised points or rays, placed alter- 

 nately with foliage. The form of their creation, which has latterly 

 been superseded by the creation by letters patent, was by the king's 

 girding on the sword of the intended earl, and placing his cap and 

 coronet on his head and his mantle on his shoulders. The king styles 

 all earls, aa well a* the other ranks of the higher nobility of peerage, 

 his cousins. An earl is entitled right honourable, and takes precedence 

 next after marquesses, and before all viscount* and barons. When a 

 marquess has an earldom, his eldest son is called earl by courtesy ; but 

 notwithstanding this titular rank, he is only a commoner, unless he be 

 summoned to the House of Lords by such title. So the eldest sons of 

 dukes are called earls where their fathers have an earldom but no 

 inarquiaate, as the Duke of Norfolk, &c. 



The number of English earls in the House of Lords is at present 

 (1859) 110. Of Scotch earls there are 42, and of Irish earls 65, of 

 whom many have seats in the House of Lords in consequence of 

 possessing a British peerage also. 



EARL MARSHAL OF ENGLAND, one of the great officers of state, 

 who >hl and orders all great ceremonials, takes cognisance of all 

 matters relating to honour, arms, and pedigree, and directs the pro- 

 clamation of peace and war. The curia militari, or court of chivalry, 

 was formerly under his jurisdiction, and he is still the head of 

 the heralds' office, or college of arms. Till the reign of Richard II., 

 the possessors of this office were styled simply marshals of England ; 

 the title of earl marshal was bestowed by that king, in 1386, on 

 Thomas Lord Mowbray, Earl of Nottingham. The office is now 

 hereditary in the family of Howard, and is enjoyed by the Duke of 

 Norfolk. 



EARTH (Astronomy). In the language of astronomers, the earth 

 U rarely treated as a planet. All the phenomena connected with its 

 motion are seen in the apparent motion of the SUM, to which article we 

 therefore refer. 



EARTH, CONTROVERSY ON THE MOTION OF THE. [Mo- 

 TIOX or THE EARTH.] 



EARTH, KKJfHK OK THE. [GF.ODEST.] 



EARTH, MEAN DENSITY OF THE. The quantity of matter 

 which the earth contains must ultimately be our only guide to that of 

 any other planet. The relative masses of two planets can be found by 



calculation of the effects which they produce upon any third body ; 

 l't the mass of a planet with reference to any given substance, aa 

 water, cannot be directly determined upon any instance except -.<- 

 own earth. Perhaps a problem could hardly be proposed which would 

 seem more impracticable to the ordinary reader than that of deter- 

 mining the mean density of the earth. It amounts to asking this : 

 If it were required to substitute for the earth a solid globe of tin- 

 same sixe, but of anifurm material, in such a manner that the absolute 

 weight of bodies on its surface should remain the same, and the attrac- 

 tion of the whole on other planets remain the same what must the 

 material be? 



Of necessity this question was started by Newton, whose system 

 wag the first in which it became of much interest. Having no means 

 of submitting it to experiment, he made one of those sagacious guesses 

 which, had they been collected and preserved, would alone have kept 

 his memory alive. " Unde cum terra communis suprema quasi duplo 

 gravior sit quam aqua, et paulo inferius in fodims quasi tri; 

 quadruple aut etiam quintuplo gravior reperiatur : vensimile est quod 

 copia material totius in terra quasi quintuplo vel sextuplo major nit 

 quam si tota ex aqua constaret." (' Principia,' iii. 10.) That is, he 

 judged the earth to be between five and six times as massive as the 

 same bulk of water ; which is the truth. 



The relative masses of two planets ore determined by the observa- 

 tion of their effects upon a third. Two preliminaries are required : 

 first, the great assumption of the theory of gravitation, that any two 

 particles of matter must attract one another with forces which at 

 different distances are directly as their masses, and inversely as the 

 squares of those distances; secondly, the mechanical consequence of 

 this law of action, namely, that two spheres, having their centres at any 

 given distance, attract one another in the same manner as if each were 

 collected in its centre. Without describing the mode of arriving at 

 such a result from observation, suppose it is ascertained that two 

 planets, A and B, whose distances from a third are as 4 to 3, attract 

 that third with forces which are as 7 to 2. If both planets be brought 

 to the distance 1 from the third, the attraction of the first will be 

 made (4 x 4, or) 1C times as great as before, and that of the second 

 (3 x 8, or) 9 times. Consequently, the new attractions will be as 7 x 

 16 to 2 x 9, or as 112 to 18. But at equal distances the attractions are 

 in the proportion of the masses ; therefore these masses are as 112 t<> 

 18. Now suppose the radii of the planets to be as 3 to 2 ; then tli.-ir 

 solidities are as 27 to 8, and if the densities (mean) are 8 and 5', the 

 masses are as 278 to 8!'. Therefore 27S : 88' : : 112 : 18, or 8 : 8' : : 

 112 x 8 : 18x27 : : 896 : 486. If then the mean density of either 

 planet be known, that of the other can be found. 



The principle of the preceding process exists in every attempt which 

 has been made to find the mean density of the earth. The earth itself 

 is made one of the planets ; some known substance, a mountain or a 

 ball of lead, is made the other planet. The attracted body is not a 

 planet, but a pendulum or a plumb-line, and the effect of the mountain 

 or ball of lead upon the plumb-line is measured, that of the earth being 

 cither measured or previously known. The actual attraction of the 

 mountain or ball of lead being thus determined, its effect as it would 

 be if placed at the centre of the earth can be calculated ; which effect 

 is to the effect of the earth as the moss of the mountain or ball of lead 

 to that of the whole earth. The result of this process, as usual, is 

 condensed into a formula, in which the mode of making the steps is 

 lost sight of : but the above is nut the less the manner in which the 

 experiment must be explained. 



The hint given by Bouguer, the experiment of Maskeleyno, and those 

 of Cavendish and Zach, have been briefly described in ATTRACTION. 

 Since their time two repetitions of Cavendish's experiment have been 

 made : the first, by Dr. Reich, of Freyberg, of which an accoui 

 published in 1838; the second, by Mr. Baily, at the desire of the 

 Astronomical Society, and at the expense of the government. (' 

 Ast. Soc.,' vol. xiv.) The former obtained the same result as ( 

 dish, but the experiments were few in number; the latter obtained a 

 result slightly differing from that of Cavendish, but in so many different 

 ways and by so large a number of experiments, that it is impossible to 

 doubt the superior correctness of the conclusion. Wo shall give such 

 a slight general account of this process (which is substantially that of 

 Cavendish) as our limits will admit, referring to the volume already 

 cited for more detail : very few experiments nave been either so well 

 performed or so satisfactorily described. 



A TOBSIOX pendulum (76 inches long) was provided, moving on a 

 single or double metal wire, or on a double silk lino, the mode of sus- 

 pension being varied from time to time. At each end was suspended 

 a metal or other ball ; and these balls (a and b) were the principal 

 attracted substances. The whole torsion-rod with the Bii."i><'n.-ii>n was 

 inclosed in a case, with a glass at one end. Large leaden balls (\ and 

 B) of about twelve inches diameter (the attraction of which on the 

 torsion pendulum is the quantity to be measured in the experiment) 

 were made to travel on a frame in such manner that they could quickly 

 be brought up laterally on opposite sides of the balls, as in the diagram. 

 We must leave out the whole account of the precautions against 

 electricity or radiation, the manner of noting the actual position of 

 the pendulum, Ac., and confine ourselves to the principle of the 

 experiment. 



When a torsion pendulum, such as that described, is left to itself, 



