MEC 



MEG 



guish them from those of a uniform crys- 

 talline texture, which are of chemical 

 origin. 



MECHANICAL PHILOSOPHY. The 

 application of mechanics to physical 

 science. Hence the term Mechanists 

 was applied to those philosophers who 

 referred all the phenomena of the uni- 

 verse to the agency of mechanical forces, 

 in opposition to the Dynamical school, 

 which insists on a living principle in 

 nature, antecedent to, and distinct from, 

 the visible phenomena of nature. 



MECHANICAL POWERS. The gene- 

 ral designation of six simple machines, 

 viz., the lever, the pulley, the wheel and 

 axle, the inclined plane, the wedge, and 

 the screw. All the different compound 

 engines, however mixed or complex 

 their construction, consist only of various 

 combinations of these few individual 

 powers. 



MECHANICAL SOLUTION. A term 

 applied to the solution of those geometri- 

 cal problems which require other instru- 

 ments {machincE) than those employed in 

 the constructions of pure geometry. The 

 latter being effected merely by straight 

 lines and circles, require only a rule and 

 compasses. 



MECHA'NICS innxavr), a machine). 

 The science which treats of the equili- 

 brium and motion of bodies. That part 

 of the subject which relates to the condi- 

 tions of equilibrium is called statics; 

 while that which investigates the motion 

 which a body acquires when the forces 

 applied to it are not in equilibrium, is 

 termed dynamics. 



MECHLO'IC ACID. A compound of 

 meconia, a neutral principle existing in 

 opium, and chlorine, discovered in 1835 

 by Couerbe, 



MECO'NIC ACID (m»7k«i/, a poppy). 

 A tribasic acid, obtained from poppies, 

 constituting the characteristic acid of 

 opium. Its congeners are the comenic, 

 which is bibasic ; and the parameconic, 

 which is monobasic. 



MEDIUM {medius, middle). In Phy- 

 sics, the space or substance in which 

 bodies subsist or move. Newton con- 

 ceived a universal medium, or ether, 

 more subtil than air, through which the 

 heavenly bodies move. This idea favours 

 the theory of the transmission of light by 

 undulation. 



MEDU'LLARY RAYS (werfw^a, pith). 

 A botanical term applied to the thin ver- 

 tical radiating plates of muriform cellular 

 tissue, which serve to connect the centre 

 213 



of an exogenous stem with the circum- 

 ference. They are technically called the 

 silver grain, and they produce, on a lon- 

 gitudinal section of the stem, the glancy 

 lustre which so remarkably characterizes 

 the plane and the sycamore. 



MEDU'LLARY SHEATH {medulla, 

 pith). The sheath which immediately 

 surrounds the medulla, or pith, of exo- 

 genous plants. It consists of spiral ves- 

 sels and woody tissue, and forms an ex- 

 ceedingly thin layer. 



MEDU'LLIN {medulla, marrow). The 

 name given by Dr. John to the porous 

 pith of the sun-flower. 



MEDUSA. A genus of the Acalephae, 

 or Sea-nettles ; marine radiated animals, 

 without shells. The name is derived 

 from their organs of motion being spread 

 out like the snaky hair of the fabulous 

 Medusa. On being touched, they induce 

 redness and a tingling sensation ; they 

 are also supposed to occasion, in certain 

 latitudes, the phosphorescent appearance 

 of the sea. 



MEE'RSCHAUM. JScume de mer. A 

 silicate of magnesia; a greasy, soapy 

 substance, occurring in Cornwall. In 

 Germany and Turkey it is manufactured 

 into tobacco pipes. 



MEGALO'PTERANS {fxe^a^, great, 

 irrepov, a wing). A family of Neuropte- 

 rous insects, characterized by their large 

 wings horizontally folded. — Latreille. 



MEGALOSAU'RUS {^e-niXn cavpa, 

 great lizard). A fossil gigantic amphi- 

 bious animal of the saurian, or lizard and 

 crocodile tribe, found in the oolitic slate 

 at Stonesfield, near "Woodstock, and other 

 localities. 



MEGANY'CTERANS ()ue7af, large, 

 vyKTepis, a bat). A tribe of Cheiropterous 

 animals, including the largest species of 

 bats, or *' flying foxes." 



MEGAPODI'ID^. The name given 

 by Mr. Swainson to a family of the Ra- 

 sores, from the genus megapodius, \fh.\ch, 

 with the allied genera, is referred by 

 other naturalists to the Cracidae, or 

 Curassows. 



ME'GASCOPE (iueyaf, large, o-KOTreo), 

 to examine). An optical instrument, 

 constructed on the principle of the solar 

 microscope, for examining bodies of large 

 dimensions. 



MEGATHE'RIUM (/xe^a ^Mptov, great 

 beast). A fossil extinct quadruped, re- 

 sembling a gigantic sloth, and character- 

 istic of the later tertiary period on the 

 continent of South America. This, and 

 some other genera of extinct Edentata, 



