MAG 



[ 154 



M A L 



in France are said to contain ten per cent, 

 of magnesia. Magnesia is present in all 

 the inferior stratified rocks, with the ex- 

 ception of quartz rock, (without mica,) 

 and certain eurites, or compact felspars. 

 In the detrital rocks it is also common, 

 particularly when mica forms any consi- 

 derable portion of them. There are few 

 limestones which do not contain mag- 

 nesia. It is an essential ingredient of 

 dolomite, carbonate of magnesia consti- 

 tuting more than forty per cent, of that 

 rock. Magnesia is also disseminated 

 through the waters of the ocean, muriate 

 of magnesia forming from '004 to '005 of 

 their mass. 



MAGNE'SIAN. Containing magnesia ; re- 

 sembling magnesia. 



MAGNE'SIAN LI'MESTONE. A marine de- 

 posit, belonging to the new red sandstone 

 group. It lies above the red conglome- 

 rate and below the variegated sandstone. 

 It is composed of carbonate of lime and 

 carbonate of magnesia. The magnesian 

 limestone of this country is a dolomite of 

 a yellow or yellowish-brown colour ; it is 

 distinctly stratified, the strata varying 

 from a few inches to several feet in thick- 

 ness. This deposit is fossiliferous, and 

 certain shells, products, appear for the 

 first time in the magnesian limestone. 

 Magnesian limestone forms the most du- 

 rable building-stone, and it is of this that 

 the two new houses of parliament are to 

 be built. It is to be lamented that Wa- 

 terloo Bridge was not built of magnesian 

 limestone instead of felspathic granit,e, a 

 very perishable kind of stone. Magnesian 

 limestone is also called zechstein. Where 

 the magnesia is in excess the land is ste- 

 rile, but when it is not in excess, the soil 

 is fruitful, and, as a subsoil, healthful. 



MA'GNESITE. A mineral of a white or yel- 

 lowish-white colour. It occurs massive, 

 tuberose, reniform, and vesicular. Its 

 fracture is conchoidal. Opaque. Speci- 

 fic gravity 2'881 . It is infusible, and be- 

 fore the blow-pipe becomes so hard as to 

 scratch glass. It occurs in serpentine. 



MAGNE'SIUM. The metallic basis of mag- 

 nesia, magnesia consisting of magnesium 

 61-4, oxygen 38-6. 



MAGNE'TIC IRON ORE. The Fer oxydule 

 of Haiiy ; Magnet eisenstein of Werner. 

 A black ore, possessing a slight metallic 

 lustre. Occurs regularly crystallized ; in 

 granular concretions ; massive and disse- 

 minated. It is magnetic, sometimes suf- 

 ficiently so to take up a needle. It oc- 

 curs in beds in primary and transition 

 rocks. This ore is very common in 

 Sweden. 



MA'GNETISM. (magne'tisme, Fr.) The 

 tendency of the iron towards the magnet, 

 and the power of the magnet to produce 



that tendency ; the power of attraction. 

 Very delicate experiments have shewn 

 that all bodies are more or less susceptible 

 of magnetism. Many of the gems give 

 signs of it ; titanium and nickel always 

 possess the properties of attraction and 

 repulsion. But the magnetic agency is 

 most powerfully developed in iron, and in 

 that particular ore of iron called the load- 

 stone, which consists of the protoxide 

 and peroxide of iron, together with small 

 portions of alumina and silica. A metal 

 is often susceptible of magnetism if it 

 contain only the 130,000th part of its 

 weight of iron, a quantity too small to be 

 detected by any chemical test. One of 

 the most distinguishing tests of magnet- 

 ism is polarity, or the property a magnet 

 possesses when freely suspended, of spon- 

 taneously pointing nearly north and south, 

 and always returning to that position 

 when disturbed. Induction is the power 

 which a magnet possesses of exciting 

 temporary or permanent magnetism in 

 such bodies in its vicinity as are capable 

 of receiving it. By this property the 

 mere approach of a magnet renders iron 

 or steel magnetic, the more powerfully 

 the less the distance. Iron acquires 

 magnetism more rapidly than steel, yet it 

 loses it as quickly on the removal of the 

 magnet, whereas the steel is impressed 

 with a lasting polarity. There can hardly 

 be a doubt but that all the phenomena of 

 magnetism, like those of electricity, may 

 be explained on the hypothesis of one 

 ethereal fluid, which is condensed or re- 

 dundant in the positive pole, and deficient 

 in the negative. Mrs. Somerville. 



MAIL, (maille, Fr. maglio, It.) Armour 

 for the defence of the body. 



MAI'LED. Protected by an external coat or 

 covering, of scales or hard substances, 

 which protects the body. 



MA'LACHITE. (malachite, Fr. malachite, 

 It.) An oxide of copper combined with 

 carbonic acid. It is of a blue colour, and 

 occurs in mineral veins and in beds of 

 gneiss, mica-slate, limestone, red-sand- 

 stone, &c. 



MA'LACOLITE. A variety of augite of a 

 darkish green colour. 



MALACO'STRACAN. Certain orders of 

 Crustaceans, distinguished by having ses- 

 sile eyes, imbedded in the substance of 

 the head. 



MALLEABILITY, (malleabilite, Fr.) The 

 property or capability of being hammered 

 into different forms without breaking. 



MA'LLEABLE. (malleable, Fr. malleabile, 

 It.) That may be spread out by ham- 

 mering. Of all the metals, the most 

 malleable is gold, five grains of which 

 may be hammered out so as to cover a 

 surface of 273 square inches, the thick- 



