740 



MECHAIN MECHANICS. 



and convenient ; the Iiotises of stone, of three or four 

 stories, built in the Persian or Iiuiian, rather than the 

 Turkish style, having' neat fronts, ornamented exter- 

 nally with paintings ami mouldings. Many quarters 

 arc now abandoned to ruins, und of the houses that 

 remain, two-thirds are unoccupied. Mecca is a city 

 of the greatest celebrity among the Mohammedans, 

 and contains the three holiest things in the Moham- 

 medan world, the well Zemzem, the Caaba (or 

 house of God), and the Black Stone. Zemzem is 

 l>elieved, by the followers of Mohammed, to be the 

 identical spring which gushed forth in the wilderness 

 tor the relief of Hagar and Islmiael ; and marvellous 

 efficacy is ascribed to its waters, in giving health to 

 the sick, imparting strength of memory, and purifying 

 from the effects of sin. The Caaba, or Kaaba, is of 

 great antiquity. (See Kaaba.) The Black Stone, 

 the principal wonder of the place, is said to have 

 been brought by the angel Gabriel, and to have been 

 originally of a dazzling whiteness. The grand cere- 

 mony through which the pilgrims pass is that of going 

 seven times round the Kaaba, kissing each time the 

 sacred stone. It is generally supposed to be a me- 

 teoric stone. Forty eunuchs are at present maintain- 

 ed there, by the revenues of the temple and the gifts 

 of the pious. Mecca is entirely supported by pilgrims 

 from every part of the Mohammedan world ; but the 

 number is now much less than formerly, owing partly 

 to the decay of religious zeal, and the decline of 

 power and wealth of the Mohammedan states ; and 

 partly, also, to Mecca's being subject to the incur- 

 sions of the Wahabees. The commerce, now greatly 

 diminished, consists chiefly in the productions and 

 manufactures of India. Notwithstanding the sacred 

 character of the city, it has now little reputation for 

 learning, and Burckhardt found no book shops in the 

 place. No Christian is allowed to enter Mecca, and 

 its territory is regarded as sacred to a certain distance 

 round, which is indicated by marks set up. The 

 male Meckaways are all tattooed at the age of forty 

 days, to prove their origin in the holy city. Mecca 

 was taken by the Wahabees, in 1804, but soon after 

 recovered by the sherif Galib. It was again cap- 

 tured in 1807, and again delivered by Mohammed Ali, 

 pacha of Egypt, in 1818. For the ceremony which 

 takes place on the arrival of the pilgrims, see Arafat. 

 MECHAIN, PIERRE FaANgois ANDRE, an astro- 

 nomer, born Aug. 16, 1744, at Laon, went to Paris 

 in 1772, and was there favourably received by La- 

 lande. His discovery and calculation of two comets, 

 in 1781, rendered him generally known ; and he was 

 among the first to delineate the probable orbit of the 

 newly discovered planet Uranus. In 1782, the aca- 

 demical prize for the best essay on the return of the 

 comet of 1661 was awarded to him ; and, when it 

 appeared again, eight years afterwards, his calcula- 

 tions were proved to be correct. In the course of 

 eighteen years, Mechain discovered fourteen comets, 

 the orbits of which he calculated. No important 

 celestial phenomenon escaped his notice, and his 

 observations were recorded in the Connaissance des 

 Temps, which was edited by him from 1788 to 1794. 

 When the constituent assembly ordered the prepara- 

 tion of a new system of measures, based on the meri- 

 dian of the earth, Mechain was one of the astrono- 

 mers appointed to measure the arc of the meridian 

 between Dunkirk and Barcelona. He received, for 

 his part of this difficult operation, the portion of 

 country lying between Barcelona and Rhodez, where 

 no measurements had previously been made. Politi- 

 cal causes also contributed to embarrass his progress ; 

 and the Spanish government not only interrupted his 

 triangulation, but detained him for some time pris- 

 oner. He was enabled to resume his labours in 

 1803, with the intention of extending them to the 



Ha learic isles. He died at Valencia, in 1804, of the 

 yellow fever, a victim of his exertions in the cause of 

 science. Besides his treatises in the Connaissnnce 

 ties Temps, and his memoirs on the different comets, 

 we find, also, the results of his observations in the 

 Base du Systhne mitriyue dicimal, by Delambrc 

 (Paris, 180610,3 vok). 



MECHANICS (from ^^aiti, a machine or con- 

 trivance) is the science which treats of forces and of 

 motion. (See force.) It had, probably, its origin 

 in the construction of machines, and an important 

 branch of it, practical mechanics, investigates their 

 construction and effects. Forces, acting upon bodies, 

 may either produce rest or motion. In the former 

 case, they are treated of under statics, in the latter, 

 under dynamics (q. v.). Hydrostatics (q. v.) and 

 hydraulics (q. v.) respectively treat of fluids, at rest, 

 or in motion. 



When a body is acted on by two or more forces, 

 which counteract each other, so that no motion is 

 produced, the body and the forces are said to be in a 

 state of equilibrium. The conditions of equilibrium 

 form the subject of statics. 1. A body acted upon by 

 two equal and opposite forces will remain at rest. 

 In this case, either of the two opposite forces may be 

 made up of several parallel forces. It is then said 

 to be the resultant of those forces. 2. If two forces 

 act, with reference to each other, obliquely upon a 

 body, they may be counteracted by a third (called 

 also their resultant). If the two forces be repre- 

 sented, in direction and intensity, by two contiguous 

 sides of a parallelogram, their resultant will be 

 represented, in direction and intensity, by its dia- 

 gonal. This is called the parallelogram of forces. 

 Thus, if a body, A, 

 be acted upon by two 

 forces, one of which 

 would cause it to move 

 from A to B in any 

 given time, and the 

 other would cause it 



to move from A to C in the same time ; then if these 

 forces act upon the body at one instant, it will move 

 in neither of the lines AB, AC, but in the line AD, 

 which is the diagonal of the parallelogram of which 

 the two lines AB and AC are containing sides ; and 

 by the action of the two forces, the body will be found 

 at D, at the end of the time that it would have been 

 found at B or C, by the action of either of the forces 

 singly. If the two forces which urge the body, both 

 produce a uniform motion, the resulting motion will be 

 in a straight line; but if one of them act by impulse, 

 which would produce a uniform motion, and the 

 other act constantly so as to produce an accelerated 

 motion, the resulting motion will be in a curve. 

 Thus, if the ball of a cannon were sent in an horizon- 

 tal direction, it would never deviate from this 

 straight line unless acted on by some external 

 force. The force of gravity acts on the body con- 

 stantly, so as to draw it to the earth, by an uniformly 

 accelerated motion ; and the result is, that the ball 

 will move in a curve, and this curve may be easily 

 shown to be that of the parabola. The resistance of 

 ttieair being taken into account together with these 

 circumstances, constitute the bases of the science ot 

 gunnery. 3. If several forces, acting at once upon 

 a body, can be represented, in direction and inten- 

 sity, by several sides of a polygon, they may be 

 counteracted by a single force, acting in a direction 

 and with an intensity represented by the side which 

 would be necessary to complete the polygon. 



All the changes which come under our observa- 

 tion, are the consequence of motions produced by the 

 action of a few great elementary forces. The con- 

 sideration of the motions which take place among 



