Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/887

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MACAO, in zoology, the name of a fpecics of par- rot. See the article Macaw, Suppl. MACAW, (Suppl.) or Macaw-Zw, in botany, the name of a (pecics of palma, or Phcenix. See the article Phoenix, Suppl.

MACHINE (Cycl.) — The fimple Machines, or mechanical powers, according to their different ftructure, ferve for differ- ent purpofes ; and it is the bufinefs of the fkilful mechanilt to choofe them, or combine them, in the manner that may be beft adapted to produce the effect required, by the power which he is pofTeffed of, and at the leaft expence. The lever can be employed to raife weights a little way only, unlefs the engine itfelt be moved ; as, for inftance, to raife ftones out of their beds in quarries. But the axis and wheel may ferve for raifing weights from the greateft depths. Pullies being eafily carried, are therefore much employed in fhips. The wedge is excellent for feparating the parts of bodies ; and the fere w for compreffing or fqueezing them together j and its great friction is even fornetimes of ufe, to preferve the effect already produced by it. The ftrength of the Machine, and of its parts, muft be proportioned to the effects which are to be produced by it. Thus, when the center of motion is placed between the power and the weight, itmuftfuftaintbe fum of their efforts : a fmall ballance, therefore, ought not to be employed for weighing great weights ; for thefe diforder its ftructure, and render it unfit for ferving that purpofe with accuracy. Neither are great Machines proper for producing fmall effects. It were to be wifhed, that we had a detail of all thefe things drawn up by fome fkilful and experienced me- chanift.

From thefe ftmple Machine:, compounded ones are formed by various combinations, and ferve for different purpofes ; in all which the fame general laws take place ; and particularly this, that the power and weight fuftain each other, when they are in ihe inverfe proportion of the velocities which they would have in the directions wherein they act, if they were put in motion.

But in practice the friction of Machine: is to be confidered, without allowing for which we fhall often find ourfelves at a lofs Seethe article Friction, Append. Accurate defcriptions and draughts of Machine: would be a very curious and ufeful work. But to make a collection of this kind as advantageous as poflible, it (hould, befides the defcriptions of Machine:, contain an analyfis of them ; pointing out their advantages and difadvantages ; the rcafons of the con ft met ions ; and the general problems, implied in thefe conffructions, with their folutions, fhould be extracted. None of thefe things have as yet been done, in a complete and fatisfactory manner, in any treatife of this kind. How- ever, many curious particulars may be gathered from Strada, Beffon, Btroaldus, Auguftinus de Ramellis, Buckler, Leu- pold, Beyer, Limpergb, Van Zyl, Perault, and others ; a ihort account of whole works we find in Wolfii commcritatio dc prsecipuis fcriptis mathematicis. Elem. Mathef. tJniv. Tom. 5. pag. 84. feq. To thefe muft be added, Monficur Behdor's Architecture' Hydraulique, and Dr. Defaguliers's Courfe of Experimental Philofophy. The Royal Academy of Sciences at Paris have alfo given us a collection of Ma- chine: and inventions approved of by them. This work, publifhed by Monfieur Gallon, confifts of fix volumes in 4to, containing engraved draughts of the Machines, with their de- fcriptions annexed. But a complete inftitution of practical Mechanic: is ftill wanting. See the article Mechanics, Append.

Machine of Marly (Cycl.) ^- This Machine was made by a common mechanic of Liege, and has a great' many ex- cellent contrivances ; but jet does not raife all the water that it might have done,' becaufe the maker did not know how to give the River Seine all the advantages of which it was capable. Hence appears the neceflity of a mechanic's being well acquainted with mathematics ; or that able mathemati- cians would apply themfelves to mechanics more than they do, and not think it below them to direct workmen. See Defagul. Exper. Philof. Vol. II. p. 442, to 449. According to Dan. Bernoulli's computation, the effect of the Machine of Marly is not more than -^ of its abfolute force ; that is, there is a lofs of a_s of that force. Dan. Bernoul. Hydrodyn. p. 182.

Machines for raifing water. See the article Raifing Wa- ter, Append. See alfo the article FiRE-engine.

MACROCERCI, the name eitablifhed by Dr. Hill for a large genus of animalcules, diftinguifhed from all others by having tails longer than their bodies. See the article Animalcule, Cycl. Suppl. and Append.

MAD-iuorr, the Englifli name of a genus of plants, called by botanifts Alyffon, See the article Alysson, Suppl,

MADDER (Suppl)— Pw/v-Madder, the Engl i(h name of a genus of plants, known among authors by that of Ru- beola . See the article Rubeola, Suppl. MADNESS — Dr. Michelotti relates the cure of a young man, who, after being exposed to very hot weather at fea, and having committed violent debauches in drinking, became mad, without any fever. He was cured by violent bleed- ing, ftarving, weak very cold drink, the cold bath, and pouring cold water on his head. Hilt, de 1'Acad. des Scienc. 1734. See the article Mania, Suppl. MAGNESIA, the fame with Manganefe. See the article

Manganese, Suppl. MAGNET (Cycl.) — Armed Magnet. See the article Load-stone, Suppl.

The power of natural Magnet: may be greatly increafed by art ; and this feems to have received farther and very great improvements from Dr. Knight. See Philof. Tranf. N° 474. p. 163. feq.

The poles of natural Magnets may be inverted, or their di- rections may be changed. Remarkable inftances of this may be feen in the Phil. Tranf. N° 101. p, 164. feq. and N° 476. p. 36. feq. Thus the magnetical virtue may be placed in fuch a manner, that the two oppofite ends of a fione fhall become, both, fouth poles ; and the middle quite round, a north pole. Or, the two oppofite ends may be north poles ; and the two oppofite fides fouth poles. Half of the furface of the (tone may be made a north pole, and the other half a fouth pole. A north pole may be placed fo as to be furrounded by a fouth pole ; and at the other end of the Hone, a fouth furrounded by a north pole ; fo that the edges of each furface have a pole of a different denomination from that which occupies the middle. See Phil. Tranf. N* 476. p. 361. feq. ArtificlalM agxet. Artificial Magnets have been made in great perfection by the before mentioned gentleman. See the Phil. Tranf. 1^474, p. 161. feq. where various experiments of the force of thefe Artificial Magnets are recorded ; one in particular weighing, without its armour, juft an ounce, and with the armour, cramps, and rings, one ounce 17 pen. wt. lifted fix pounds ten ounces troy weight. See pag. 166, N° ci't.

It is hoped, that Doctor Knight will foon oblige the world with his difcoveries in magnetifm. In the mean time, the ingenious Mr. Canton has found out a me- thod of making artificial Magnets, without the ufe of, and yet far fupcrior to, natural ones. This gentleman has fuc- ceeded fo well in his attempts to convey a confiderable mag- netic virtue to bars of hardened ftecl, as to be able to impreg- nate fuch bars with this virtue, to as high a degree as any of the fame weight and dimenfions which he had yet feen or heard of; and to as high a degree, as, he apprehends, the fame bars in their prefent ftate are capable of being impreg- nated. Mr. Canton has publifhed the description of his pro- cefs, with fuch directions, that any perfon may readily per- form the fame.

The apparatus, befides the bars of hard and foft ffeel, confifts only in an iron poker and tongs, the larger they are, and the longer they have been ufed, the better. But fur the appli- cation of this apparatus, we muft refer to the ingenious au- thor himfelf, who has expreffed himfelf clearly and concifely, and added figures for the more eafy intelligence of his pro- cefs. See a method of making artificial Magnets, without the ufe of natural ones, by .John Canton, M. A. London, 1751. See alfo Phil. Tranf. Vol. 47. p. 31.

MAGPYE, in ornithology, the Englifh name of a large order of birds. See the article Pica, Suppl.

MAHOGANY, a well known, and, juftly, much valued wood, brought from Jamaica, and other parts of the Weft- Indies.

It is the wood of a very beautiful tree, with pinnated leaves, but hitherto not reduced to any certain clafs or genus of plants. Catefby, indeed, who faw only the withered remains of its flower, tells us, that he could plainly perceive it to be pentapetalpus, or confuting of five leaves. Its fruit has fome, tho' but a remote, refenlblance to that of the pine.

MAIDEN-A<«V (Suppl.) — Black MAiDEN-iWr, a name fometimes given to the Fillcula, or dwarf Fern. See the article Filicula, Suppl.

Englljh Maiden'-ZmiV, the name of a genus of plants, cal- led by botanifts Trlchomancs. See the article Trichoma-

NES, Suppl.

White Maiden-/wjV, the name by which fome call the Ruta-murarla, or wall-rue. See the article RuTA-mwra- ria, Suppl.

MAILLS, on (hip-board, are fquare machines, compofed of a number of rings interwoven net-wife, and ufed for rubbing