Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/862

 GUN

GUN

GUARANTY, in politics, an engagement of mediatorial or neutral ftates, whereby they pledge their faith, that the ar- ticles of a particular treat)' fnali be> inviolably obferved on both fides.

This engagement implies, that the guarantees are obliged to aflift the party invaded contrary to the treaty, againft the in- jurious agreflbr; but not if the war is occafioned by any other caufes than the violation of the articles of peace. Puffendorjf, Law of Nature and Nations, book: VIII. ch. viii. §7.

GUAVA, a name fometimes given to the guajava of Tournc- fort. See the article Guajava, Suppl.

GUERKINS, a kind of cucumbers for pickling, otherwife called gherkins, Diet. Ruft. in voc.

GUERNSEY-/r7/y, a name ufed for a genus of plants, called by fome amaryllis, and by others lillo-nardjjus. See the ar- ticle Lilio-Narcissus, Suppl.

GUILLEMITES, an order of monks in Flanders, whofe ha- bit refembles that of the Ciftertians : they follow the rule of St. Auguftine, and are governed by a fuperior, who does not take the title of provincial, aad is elected every four years See Srougbton's Diet. Rehg. in voc.

GVlNEA-benzveed, in botany, a name by which fome call the peti-veria of botanical writers. " See the article Petiveria Suppl.

GuiNEA-pepper, the Engl ifh name of a genus of plants, called by authors capficum. See the article Capsicum, Suppl.

GuiNEA-w£i?tf/, a name fometimes given to the maiz, or In- dian corn, called by bbtamfts yucca. See the article Yucca, Suppl.

Guinea-kwtb, in the hiftory of infers, the fame with what zoologifts call chxtia. See the article ChjETIA, Append.

GULO, in zoology, a name fometimes given to a ipecies of mujlela. See the article Glutton, Append.

GUM (Suppl.) — Grew, in his Anatomy of Plants, makes the following remarks concerning the import of the word gum, and the diftincrion thereof both from a rofin and a muci- lage.

A rofm, he obferves, is originally a turpentine, or acidulous liquor, having an exceeding fmall quantity of watery parts mixed therewith ; and which, for that reafon, will not be diuolved in water, but only in oil : of this kind are maftic, benzoin, tacamahaca, commonly called gums, though, ftricV- ly fpeaking, they are all true rofins.

A gum-, on the other hand, is originally a milky liquor, hav- ing a greater quantity of water mixed with its oily parts; and which, for that reafon, diflblves either in water or oil : of this kind are fagapenum, opopanax, ammoniac, &c, A third fort ef gum is that which is unoily ; and which, there- fore, dilTolves only in water, as gum arable, the gum of the cherry-tree, &c.

Thefe laft fubftances, though commonly called gums, are only dried mucilages; being originally nothing elfe but the muci- laginous lymph ifiuing from the veflels of the tree, in the fame manner as it does from comfrey, mallows, fefr. and even from the cucumber ; the veflels thereof, upon being cut acrofs yielding a lymph which is plainly mucilaginous, and which being well dried at length becomes a kind of gum, or rather a hardened mucilage.

In like manner, the gu?ns of the plumb-tree, cherry-tree, and the like, are nothing elfe but dried mucilages. If we will take the word in its widen: fenfe, all gums are ori- ginally either a terebinth, or a milk, or a mucilage. Grew, Anat. of Plants, book III. ch. iv. p. 134.. Gums, in medicine, mould always be ftrained before they are ufed, as being feldom free from drofs and other admixtures, which hinder their operation.

Dr. Pringle, in his Obfervations on the Difeafes of the Army, tells us, that gums are all powerful analeptics. See the article Antiseptics, Append.

Gum-fucccry, in botany, a name by which the cbondrilla of authors is fometimes called. See the article Chondrilla, Suppl.

GUNDELIA, in botany, a dift'tnet genus of plants called ha- cub by Vaillant; the characters of which are thefe : there is fcarcely any common cup, except the furrounding leaves; the flower is of the compound kind, uniformly tubulated, being made up of equal hermaphrodite flofcules, eonfiffing of a fino-le clavated petal, divided into five fegments at the edge; the (la- mina are five very fhort capillary filaments ; and the anthers cylindraceous, tubulated, and long : the germen of the piftil is ovated, immerfed in the receptacle, crowned with very fmall fquama;, and placed at the bottom of each flofcule ; the ftyle is filiform, and longer than the flower-petals j the ftigmata are two in number, and turned backwards ; there is no peri- carpium ; the feeds, which are tingle, roundim, and acumi- nated, being concealed in the receptacle, which is of a conic figure. Linnai Gen. Plant, p. 386.

GUNNERY (Oyd.) — Mr. Robins, from the experiments re- lated in his New Principles of Gunnery, having concluded, that the force of fired gun-powder, at the inftant of its explo- fion, is the fame as that of an elaftic fluid of a thoufand times the denfity of the common air, and that the elafficity of this

fluid, like that of air, is proportionable to its denfity, propofes the following problem :

The di mentions of ^ any piece of artillery, the weight of its ball, and the quantity of its charge being given, to deter- mine the velocity which the ball will acquire from the explo- fion, fuppofing the elafficity or force of the powder at the firft inftant of its firing to be given.

In the folution of this problem he aflumes the two following principles : r. That the action of the powder on the bullet ceafes as ibon as the bullet is got out of the piece. 2. That all the powder of the charge is fired, and converted into an elaitic fluid, before the bullet is fenfibly moved from its place.

Thefe aiTumption:;, and the conclufions before-mentioned, make the action of fired gun-powder to be entirely fimilar to that of air condenled a thoufand times ; and from thence it will not be difficult to determine the velocity of the ball aris- ing from the explofion. For the force of the fired powder di- miniihing in proportion to its expanfion, and ceafing when the ball is out of the piece ; the total action of the powder may be reprefented by the area of a curve, the bafe of which re- prefents the fpace through which the ball is accelerated ; and the ordinates to which, reprefent "the force of the powder at every point of that fpace. And thefe ordinate being in re- ciprocal proportioJi to their diftance from the breech of the gun, becaufe when the fpaces occupied by the fired powder areas 1, 2, 3, 4, CSV. the force of the powder, or the ordi- nates representing it, will be as, 1, ^, T, J, dfc. it appears that the curve will be a common hyperbola, and that the area intercepted between it, its afymptote, and the two ordinates reprefenting the force of the powder at the firft explofion and at the muzzle of the piece, will reprefent the total action of the powder on the bail. But if the ball were urged through the fame fpace, by an uniform force equal to its gravity, the total action of this force would be reprefented by a rect- angle, the bafe of which would be the bale of the curve or intercepted portion of the alymptote before-mentioned, and the height of which would reprefent the uniform force of gravity. Hence the fquare of the velocity of the ball refult- ing from the action of the gunpowder, will be to the fquare of the velocity refulting from the action of gravity, as the area of the hyperbolic fpace is to the area of the rectangle a. But the velocity of the ball refulting from gravity is o-iven, be- ing the velocity it would acquire from a height equal to the fpace through which the powder accelerates it ; and the pro- portion between the hyperbolic fpace and the rectano-le is al- io given, from the analogy of hyperbolic fpaces and loga- rithms b ; therefore the velocity of the ball arifing from the action of the fired gun-powder will be given. — [ a By prop. 39. lib. i. of Newton's Principles, » See the article Loga- rithm, Suppl.]

To give an example of this, let us fuppofe the length of the barrel of a gun to be 45 inches, its diameter, or rather the diameter of the ball to be \ of an inch ; and the fpace oc- cupied by the powder to be 2 \ inches ; to determine the velo- city which will be communicated to a leaden bullet by the explofion, fuppofing the bullet laid at firft with its furface con- tiguous to the powder.

By the theory here laid down it appears, that at the firft in- ftant of the explofion the flame will exert, on the ball Iyino- clofe to it, a force one thoufand times greater than the pref- fure of the atmofphere. But the medium preflure of the at- mofphere is efteemed equal to that of a column of water 3-2 feet high; whence lead being to water as 11,345 to 1, this preflure will be equal to that of a column of lead 34,9 inches in height, whence multiplying this by 1000, a column of lead 34900 inches high would produce a preflure equal to what iis exerted on the bait by the powder in the firft inftant of the explofion ; and the leaden ball being § of an inch in diame- ter, and confequcntly equal to a cylinder of lead on the fame bafe i an inch in height, the preflure at firft acting on it will be equal 1034900X2, or 69800 times its weight ; whence the force of gravity is to that of the powder at its firft explofion, as 1 to 69800. Now an uniform force, as 1, accelerating the ball through a fpace of 45 — 2|- = 42| inches, will give it a velocity of 15.07 feet in one fecond of time ; for this is the velocity the ball would acquire in falling from a height of 42 1 inches. And an initial force, as 69800, but diminifh- ing continually, as the hyperbolic ordinates, will, upon com- putation, be found to communicate a velocity to the ball, which will be to that communicated by gravity as 1 10.7 to 1. Therefore the velocity of the ball arifing from the action of the gun-powder will be — 110.7 X 15.07 — 1668.249 feet ia one fecond of time; that is, the ball, when it firft leaves the piece, will be carried at the rate of 1668 feet in one fecond.

As to the firft of the principles here afiumed, the author has obferved, in the Philof. Tranfact. N J 469. p. 445, that it would be found erroneous, if examined with a geometrical ri- gour ; fince it cannot be queftioned but the flame acts in fome degree on the bullet after it is out of the piece : but in ex- periment no fuch accuracy is attainable; minute irregulari-