Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/894

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MOTHER- wort, the name for two diftincl genufes of plants, the cardiaca and matr'tcaria, of botanical writers. See the articles Cardiaca and Matricaria, Suppl.

Mother of thyme, the EngHfh name of a diftinft genus. of plants, called by botaniftsy*r/iy//w». See the article Serpyl-

tUM, Sllppl.

MOUNTAIN, or Hill. It has been found by experiment, that bills, though they meafure twice as much as the plain ground they ftand on, yet the produce of one can be no more than that of the other ; and therefore in purchafing lands, the hills ought to be eftimated, not according to their fuperficies, but according to the'bafe on which they ftand. So that in fome cafes ; that is, if the foil be equally rich, two acres on the fide of a hill ought to pafs for no more than one upon the plain of equally rich land.

The reafon of this is evident ; for as long as all plants pre- ferve their upright method of growing, billy ground can bear no more plants in number than the plain at the bafe. Again, as to building on a hill, the two fides can bear only the fame number of houfes as the bafe on which it {lands. The fame holds in regard to park-pailing over an hill ; for tho' the mea- fure over it be fometimes near double the line at the bottom, yet both may be inclofed by the fame number of pales of the iame breadth. Miller's Gird. Dicl. in voc. Hills. The method often ufed for meafuring the heights of Mountains, by the finking of the mercury in the barometer, is very far from being accurate in practice. That the mercury gene- rally falls, when the barometer is carried up to a higher ground, is true, and has been known ever fince the time of Pafcal. The only queftion is, in what proportion ? and this queftion is not yet determined with fufficient accuracy. The rule followed by the generality of authors, is, that the heights of Mountains, or other rifing grounds, are as the logarithms correfponding to the heights of the mercury in the barometer, And the foundation of this rule is, that the denfity of the air is every where proportional to the weight of the fuperincum- bent air. But the application of this principle is improper in the prefent cafe, becaufe it can hold true only when the air is of the fame degree of heat, which it feldom is, on the differ- ent parts of high Mountains, in the valleys, and at the furface of the fea. In afcending the Cordelleras of Peru, for inftauce, the air is found to be of all temperatures, from the hoiteft fummer, to the coldeft winter. And experiments are di- feftly contrary to the rule. For by Father FeuilleVs obferva- tions on the Pic of Tenerif, the mercury in the barometer flood at 1 7 inches five lines Paris meafure, at the height of 13158 Paris feet above the furface of the fea, when the ba- rometer at that furface flood at 27 inches 10 lines. But, ac- cording to the rule abovementioned, the barometer on the Pic ought to have been above two inches and two lines lower than what it was found to be by the experiment. A difference may alfo be perceived between the computed and obferved heights of the barometer, at much (mailer eleva- tions ; fuch as 154.2 feet; where the obferved height of the mercury exceeded that found by computation above a line and an half; which would make a very confiderablc error in the height of the place.

From whence it follows, that the elafticity or fpring of the air at different heights, is not proportional to its denfity, or which amounts to the fame thing, that the mean degree of heat is different at different heights from the furface of the earth ; for it is well known, that a difference of heat will make a difference of elafticity in the air, its denfity remain- ing the fame. See Daniel Bernoulli Hydrodynamic. p. 213. feq.

This learned author obferves, that father Feuillee's experi- ment on the Pic of Tenerif, overturns all the rules and hypo- thefes hitherto contrived for discovering the heights of places, from the fall of mercury in the barometer. Mr. Bernoulli has given a new hypothecs of his own, and has founded fome computations on it, which agree pretty well with the expe- riments he mentions; but it were to be wiihed that this fub- ject were re-examined with more care by a greater variety of experiments than has been done hitherto. Monf. Caflim de Tlmri has given us e a detail of feveral ob- fervations made with care on two high Mountains of Auvcrgne, and upon the Mountain Canigou, one of the higheft of the Pyrenees. From thefe obfervations it appears, that the varia- tions of the heights of the mercury in the barometer, cor- refponding to the elevation of places above the level of the fea, follow no regular progreflion ; there having been found fometimes an inch of difference between the height of the

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mercury found by obfervation on the Mountain Canigou, front the height that refulted from the progreflion eftablifhed iri the Memoirs of the Royal Academy in 1703. This progref- fion being deduced from obfervations made at final! eleva- tions, proved erroneous j nor have any of the hypothefes made fince been fufficient to reconcile the irregularities iri ob- fervations, the exactitude of which admits of no doubt. [ c Mem. Acad. Scienc. 1740. p. 94.]

Mountain-W;, the name by which fome call the Saxifrage of botanical writers. See the article Saxifrage, Suppl.

MOURAILLE, or Barnacles, among farriers, is an ih- flxument compofed of two branches joined atone end with a hinge. It is commonly made of iron, and fertfes to take hold of a horfe's nofe, and keep it tight by bringing to, or almoft clofing the other end of the branches, and To tying them with a ftrap.

MOUSE (Suppl.) — Moose, in the fea language, is a large knot artificially made by the riggers on the (hip's flays. Blancklefs Nav. Expof. p, 108.

MousE-fw, a name fometimes given to the Hieracbium, or hawkweed of botanifts. See the article Hi er Ac Hi um, Suppl.

MousE-rrt/7, the Englifh name of a diftinct genus of plants, known among botanifts by that of Myofurus. See the article Myosurus, Append.

/5or-MousE, the Englifh name of a genus of animals, called by authors Sorex. See the article Sorex, Suppl.

6V«-Mouse, the Englifh name of a genus of infecls, called by Dr. Hill Aphrodita. See the article Aphrodita, Append.

MULBERRY- W/V^, a name ufed by fome for a fpecies of blite. See the article Blitum, Suppl.

MULCH, a term ufed by gardeners for rotten dung, or the like, thrown upon beds of young plants, to prelerve them from the bad effects of cold or drought.

MULES, among farriers, a diforder incident to horfes, other- wife called Scratches. Seethe article Scratches, Cycl.

MULLEIN, the Englifh name of a diflinct genus of plants, called by botanifts Verbafcum. See the article Verbas- cum, Suppl.

MULLET (Suppl.) is alfo ufed as the name of feveral fpecies of 'Trigla. See the article Trigla, Suppl.

MUNDICK (Cycl.) — This mineral fubftance is of an arfe- nical nature. See Geoffroi, in Mem. Acad. Scienc 1738. p. 107. edit. Paris.

MUS-7tffln'ffHj, a name ufed by fome for the Aphrodita, a ge- nus of fea infe£ls. See the article Aphrodita, Append.

MUSCA, Crabrmiformis and Rapax, names fometimes ult-d for the Fly. See the article A : silus, fupra.

Musca Vefpifornds, the Wafp-fiy. See the article Asilus, fupra.

MUSCLE(*Stf#/,;— f Accekratory Muscles. See the article Accelerator, Cycl.

MUSCUS, Mofs, in botany, a very comprehenfive clafs of plants, containing a great many diftinci genera- See the ar- ticle Moss, Suppl.

MUSICAL Accent, among Hebrew grammarians. Seethe arti- cle Accent, Cycl.

Musical Numbers (Suppl.) — A table of mufical numbers within any propofed limit may be thus expeditioufly formed. Place the terms of the progreflion 1, 5, 25, 125, &c. in a co- lumn under each other ; and multiply every term of this pro- greflion by 3, continually, till you forefee that the produces wilt exceed the propofed limit. Then if all the numbers thus found be doubled continually, till it be forefeen that the doub- led numbers would exceed the propofed limit ; all thefe pro- duces together, with the powers of 2, will give the ?nufical numbers required.

Thus if it were required to find all the mufical numbers within the compafs of eleven octaves ; that is, between 1 and 2048 ; form the column r, 5, 25, &c. and multiply every term by 3, continually, as in the annexed example ;

1. 3. 9. 27. 81. 343. 729, &o 5- 15- 45- '35- 405- 1215, &c 25. 75. 225. 675. 2025, &e.

I2 5- 375- H25» &c *

625, 1875, &c.

&c. ,

The numbers of which being doubled as often as poffiMe

within the limit 2048, and collected and ranged in order with

the powers of 2, will give the following numbers, 1. 2. 3. 4.

5. 6. 8. 9. 10. 12. 15. 16. 18. 10. 24. 25. 27- 30. &c.

as in the following table ;

1 Table