366 



GRAVEL 



GRAVITATION 



road -finishing material obtainable anywhere. It is 

 a pit-gravel, and abounds in oxide of iron, to which 

 it owes its binding quality and also its fine warm 

 harmonious colour. Many other pit-gravels also 

 possess this cohesive property in a high degree, but 

 are defective in colour. As possessing better bind- 

 ing properties, pit-gravels generally are to be 

 preferred to sea or river gravels ; but their defects 

 of colour often preclude their use in landscape- 

 gardening. The Kensington gravel is costly and 

 difficult to procure. On this account, and also 

 because of its similarity in colour, the most popular 

 gravel of the present time is the Dorset Pea ; but 

 it is also one of the most shifting, the flinty pebbles 

 composing it being round and about the size of a 

 pea. As the name implies, this sort comes from 

 the coast of Dorsetshire. From the shore of the 

 neighbouring county, Hampshire, is obtained 

 another pleasingly coloured flint-gravel named the 

 Lymington; and the Sussex coast furnishes two 

 sorts named Sussex Pea and Sussex Bean. The 

 prevailing form of the former is pea-like, that of the 

 latter bean-like ; hence their respective names in 

 commerce. They are found commingled on the 

 shore, and are separated by sifting. Shell-gravel 

 so called because composed of minute shells 

 entire or the fragments of larger ones is also a 

 favourite gravel, being pleasing in colour and com- 

 fortable to walk upon when not laid on very deep. 

 It is found on various parts of the British coasts 

 and on those of the Channel Islands. Musselburgh 

 gravels both shore and pit are prized in that 

 district, being good in colour, and the pit variety 

 has also fair binding properties. There are many 

 manufactured gravels, such as granite, whinstone, 

 marble, quartz, slag, glass, &c., which are crushed 

 in machines, and afterwards riddled to the desired 

 sizes. These and all the sea and river gravels are 

 used in making asphalt and other composite roads 

 and paths, some of them when skilfully combined 

 with cement imparting a very beautiful appearance 

 to the surface. 



Gravel, a disease. See CALCULUS. 



Gravelines, a fortified town in the French 

 department of Nord, is situated in a marshy locality 

 at the mouth of the Aa, 13 miles by rail ENE. of 

 Calais. A desolate-looking place now, with grass- 

 grown streets, it has an historic past, as the scene 

 of Egmont's victory over the French (1558), and 

 the place off which the English dispersed the 

 Armada (1588). It was taken by the French in 

 1644, retaken by the Austrians after a ten weeks' 

 siege in 1652, and finally recaptured in 1658 by 

 Louis XrV., who had it fortified by Vauban. Pop. 

 (1872) 4391 ; (1886) 2228 ; (1891) 4125. 



GravelottC, a village of Lorraine, 7 miles 

 W. of Metz. There, on 18th August 1870, the 

 French under Bazaine sustained a severe defeat by 

 the Germans. See FRANCE, Vol. IV. p. 783. 



Graves. See BARROW, BURIAL, CHURCHYARD, 

 CEMETERY, MONUMENTS. 



Graves, ROBERT JAMES, physician, who did 

 much to raise the status of his profession in Ire- 

 land, was born in 1797, the youngest son of the 

 Dean of Ardagh. He studied medicine at Dublin, 

 and after taking his degree visited the medical 

 schools of London, Gottingen, Berlin, Copenhagen, 

 those of France and Italy, and Edinburgh, and on 

 his return home settled ( 1821 ) in his native city as 

 a private practitioner and a teacher of medicine, 

 especially distinguishing himself by the introduc- 

 tion of improved methods of clinical study. In 

 1827 he was appointed professor of the Institutes 

 of Medicine in the College of Physicians, Dublin, 

 of which college he was chosen president in 1843 

 and 1844. He was elected a Fellow of the Royal 

 Society in 1849. Many of his most remarkable 



papers appeared in the Dublin Journal of Medical 

 Science, which was founded by him in 1832. Dr 

 Graves died on 20th March 1853. He published A 

 System of Clinical Medicine (1843) and Clinical 

 Lectures (1848). After his death his Studies in 

 Physiology and Medicine was issued in 1863 by Dr 

 W. Stokes. See Dublin University Magazine, 1842. 



Gravesend, a port and borough of Kent, on 

 the right bank of the Thames, 24 miles ESE. of 

 London. It consists of the old town, with narrow, 

 irregular streets, and of the handsome new town 

 on the high ground. In the vicinity are extensive 

 market-gardens ; and many of the inhabitants 

 are employed in fishing. Gravesend forms the 

 limit of the poi't of London ; and here pilots 

 and custom-house officers are taken on board 

 of vessels going up the river. For centuries 

 the prosperity of the town has depended on its 

 connection with the metropolis. The salubrious 

 air and beautiful scenery at Gravesend render it a 

 favourite watering-place with Londoners. It carries 

 on some shipbuilding, iron-founding, soap-making, 

 and brewing, and a considerable trade in supplying 

 ships' stores. Gravesend was incorporated under 

 Eli/abeth, and since 1867 has returned one member 

 to parliament. Pop. of parl. borough ( 1881 ) 31,283 ; 

 of municipal borough ( 1881 ) 23,302 ; ( 1891 ) 24,067. 

 Gravesend was originally a hythe, or landing- 

 place, and is mentioned as such in Domesday. 

 Around this landing-place a town grew up soon 

 after the Conquest. Here the fleets of early 

 voyagers, as that of Sebastian Cabot in 1553, and 

 of Martin Frobisher in 1576, assembled, and here 

 the lord mayor, aldermen, and city companies of 

 London were wont to receive all strangers of 

 eminence, and to conduct them up the river in 

 state. A great fire in 1850 did damage to the 

 amount of 100,000. See Arden's History of 

 Gravesend ( 1843). 



Gravina, a town of southern Italy, in the 

 centre of a rich agricultural district, 33 miles SW. 

 of Bari. Pop. 15,612. 



Graving-docks, See under Dock, page 31. 



Gravitation. It is a matter of common experi- 

 ,ence that all unsupported bodies near the surface 

 'of the earth fall to the ground, the direction of 

 their motion being towards the earth's centre. The 

 modern explanation of this phenomenon is that it 

 is due to an attractive force termed gravitation or 

 gravity, which exists between any such body and 

 the earth, in virtue of which they tend to move 

 towards one another. The motion of the earth 

 and other planets round the sun, and of the 

 various satellites round their primaries, may be 

 explained on the same ground. The mode of 

 action of this force is given in the following 

 generalisation, first explicitly given by Ne\yton, 

 and known as the Law of Gravitation: Every 

 particle of matter in the universe attracts every 

 other particle with a force whose direction is that 

 of the straight line joining the two, and whose 

 magnitude is proportional directly as the product 

 of their masses, and inversely as the square of their 

 mutual distance. 



Previous to Newton's investigations, Kepler, 

 by a truly prodigious amount of labour, had 

 deduced from the observations of Tycho Brahe the 

 following kinematical laws of planetary motion : 

 ( 1 ) The path of each planet is an ellipse, of which 

 the sun occupies one focus; (2) the radius-vector 

 (i.e. the straight line which joins the centre of the 

 sun to that of the planet) of each planet describes 

 equal areas in equal times; (3) the square of the 

 periodic time (i.e. the time during which a planet 

 makes one complete revolution round the sun) of 

 each planet is proportional to the cube of the major 

 axis of its elliptic orbit. From the second of these 



