MEC 



457 



MEC 



extremes are 2 and 6, the arithmetical 

 mean is 5 = 4. A geometrical mean 



is the square root of the product of the 

 two extremes. Thus, the extremes being 

 2 and 8, the geometrical mean is ^/-> X 8 

 = 4. A harmonical mean is the reciprocal 

 of the arithmetical mean between the re- 

 ciprocals of the given extremes. 



MEANDRI'NA. Brain-stone, brain-coral. 

 Madrepores, in which the laminae assume 

 a meandering direction. These are large 

 hemispherical corals, having their surface 

 covered with serpentine ridses and de- 

 pressions, resembling the convolutions of 

 the brain, from which circumstance they 

 have been called brain-stone. 



MEASE. The quantity of 500. 



MEA'SLES, rubeola. A disease known 

 by inflammatory fever, hoarseness, dry 

 cough, sneezing, drowsiness, during the 

 first three days, when an eruption of small 

 red spots, discernible by the touch, ap- 

 pears, and ends in mealy desquamation. 



MEAS'CRE. That by which extent or di- 

 mension is known. 1. The standard mea- 

 sure of length is a yard, and of liquids a 



gall in. 2. Any quantity assumed, as 



one Dr unity, and by which the quantities 

 of other similar things are expressed. 

 Thus the measure of a line is some other 

 assumed line, as an inch, a foot, a yard, 

 &c. In music, the interval or space of 

 time between the rising and falling of the 

 hand or foot of him who beats time, is 

 termed measure, as it regulates the time 

 of dwelling on each note. In poetry, the 

 manner of combining the quantities, or 

 the long and short syllables, is termed 

 measure, and is of different kinds; as hex- 

 ameter, pentameter, iambics, &c. In yeo- 

 logy, synonymous with beds or strata ; as 

 coal measures. 



MEA'TUS, Lat., from meo. to flow. A 

 passage, as that leading to the ear, called 

 the meatus muKtofim, aiid is either exter- 

 nal or internal. 



MECHAN'ICAL. 1. Relating to mechanics. 

 Thus, the force produced by any machine, 

 for the accomplishment of any particular 

 purpose, is called mechanical potcer ; and 

 those simple agents employed in produc- 

 ing mechanical power, and of which ali 

 machines are essentially composed, are 

 termed mechanical jntwers , and their appli- 

 cation constitutes the science of mechanics. 

 The mechanical powers are usually divided 

 into six classes ; the lever, the wheel and 

 axle, the pulley, the inclined plane, the 

 wedge, and the sorc-w ; but all these are re- 

 ducible to two, the lever aud the inclined 

 plane Some, however, regard the pulley 



as a distinct mechanical power. 2. 3/- 



ch,iHieali>hitoso]>hy is that which explains 

 the phenomena of nature, and the opera- 

 tions of corpcreal things OB the principle* 



of mechanics; viz. motion, gravity, ar- 

 rangement, disposition, magnitude of the 

 parts which compose bodies; called by 

 some corpuscular philosophy. 3. In ma- 

 thematics, the term mechanical is employe* 

 to denote a construction of a problem by 

 the assistance of instruments, as the du- 

 plication of the cube and quadrature of 

 the circle. A mechanical solution is a so- 

 lution of a problem, effected either by re- 

 peated trials, or by using lines in the 

 solution which are not truly geome- 

 trical, or by organical construction A 

 mechanical curve is one which, according 

 to Descartes, cannot be defined by any 

 algebraical equation. Leibnitz and others 

 call these curves transcendental. 



MECHANICS, from pr^wr,, a machine. 

 A branch of practical mathematics which 

 treats of motion and moving powers, tlieu 

 nature and laws, and their effects in ma- 

 chines. The term is equally applied to the 

 doctrine of equilibrium of powers, more 

 properly called statics ; and to that science 

 which treats of the generation and commu- 

 nication of motions, which constitutes 

 dynamics, or mechanics strictly so called. 

 The science is further divided into prac- 

 tical mechanics, which treats of the me- 

 chanical powers ; and rational mechanics, 

 which treats of the theory of motion. 



MECHANICS' INSTITUTES. The name 

 given to the means by which instruc- 

 tion is communicated to tradesmen 

 and mechanics, in large towns ; originally 

 put in operation by Dr. Birkbeck, in 

 1800. 



MECH'ANISX. 1. Construction of parts 

 depending on each other in any compli- 

 cated machine designed for a purpose. 



2. Action of a machine according to 



the laws of mechanics. 



MECH'ANISTS. Those philosophers who 

 refer all the changes in the universe to the 

 operation of mechanical forces. 



MECHLO'IC ACID. An acid formed bj 

 passing a current of chlorine over meco 

 nine in fusion. 



MECHO'ACAN. "White Jalap. The root of 

 the Convolvulus mechoacanna, brought 

 from Mechoacan in Mexico. It is a slow 

 purgative, but safe. 



MECON'IC ACID. An acid obtained from 

 opium (meconittni). Itcrystallisesin white 

 transparent scales, yields pyromecomc. 

 acid by distillation, and is converted into 

 oxalic acid by dilute nitric acid. 



MEC'ONINE. A peculiar principle con- 

 stituting about j^ko of P ium (>*t- 

 nium). It is soluble in water, alcohol, and 

 ether, and crystallises, from its solutions, 

 in six-sided prisms, with dihedral sum- 

 mits. It was called by M. Couerbe, whc 

 discovered it, hyt>onitronieenic ncul. 



MECO'NIUM. L Opium. The uispiisatei 



