B A L 



BALLARINA, in Orniihology, a name unJ.r which 

 Olina difcribes the white-wagtail, inotacil!'. alba. 



BALLAS, atownof Egypt, ten miles fouth of Dendcra. 



BALLAST, in Naviiaiion, any heavy matter ufed to 

 Cnk a vefiTel to its prciper depth in water, or to give it a jull 

 ■weight and counterpoife, and enable it to bear fail upright, 

 without ovtrturiimg. 



The word come?! from the Flemifh helajl, formed of le, 

 and loji or hj}. The French call it fimply LJl. In the 

 Mediterranean, quarteiage. In Latin writers of the lowtr 

 age it is denominated la/lagitwi. 



The ordinary ballall 'is fand or (loiies, ftowed in the bot- 

 tom, or hold, next the falfe keel of a vcffcl : fonietimea, iron, 

 lead, corn, or other heavy goods, ferve for ballaih — Ships 

 are faid to be iu ballaft, when they have no other loading. 



, That ballad is bell which is heavielt, lies clofell; and 

 faftert, ar.d dricft, both for the lliip, bearing a fail, Rowing 

 of goods, health of the company, and faving of caflcs and 

 other goods. If a Ihip have too much ballall, llie will draw 

 too much water ; if too little, {he will bear no fail. The 

 ballall is fometimes one-half, iometimcG a third, and fome- 

 times a fourth part of the burden of a vcfTtl, Bat there is 

 often great difference in the proportion of ballaft required to 

 prepare fhips of equal burden for a voyage ; the quan- 

 tity being always greater or lefs, according to the fliarp- 

 riefs or flatnefs of the (liip's bottom, which feanien call the 

 floor. 



Although fliips in general will not carry a fufficient 

 quantity of fail till they are laden fo deep that the furface 

 of the water will nearly glance on the extreme breadth 

 amidHiip, yet a great weight of heavy ballaft, as iron, lead, 

 &c. iu the bottom, will place the centre of gravity too low 

 in the hold ; and in this cafe, though they may be able to 

 carry a great fail, they will move heavily, and hazard being 

 difmalled by their violent rolling. The art of properly 

 balialling a Ihip is that of difpjling the materials ol which 

 it confifis, &c. fo that it may be duly poifed, and maintain 

 a juft equilibrium on the water, and be neither ioo Jliffiwr 

 too crank. In the firft cafe, though the fiiip may be able 

 to carr)' a great fail, yet its velocity will not be proportion- 

 ably increafed, whilll her malls are more endangered by her 

 fudden jerks and exctirive labouring ; and in the laft cafe 

 fhe will be incapable of carrving fail, without the danger of 

 overfetting. Stiffnefs in balialling is occafioned by laying 

 a great quantity of heavy ballaft, as lead, iron, &c. in the 

 bottom, which of courfe will place the centre of gravity 

 verv near the keel ; and cranknefs is occafioned by having 

 loo little ballaft, or by difpofing the fliip's lading in fuch 

 a manner as to raife the centre of gravity too lugh. 



As the tendency of a ftiip to pitch or roll depends, not 

 only on her form, but alfo in a greater degree upon the due 

 diftributiun of the heavieft part of her cargo, the know- 

 ledge of properly ballafting a fhip, as well as of ftowing her 

 cargo, is of great importance to the mariner. Particular 

 atteatiiin ftiouid be paid to moderate her pitching, as this 

 moll fatigues a (hip and her marts ; and it is ufnally in one 

 ofthcfe motions that mafts break, particularly when the 

 head rifes after having pitched. Rolling, indeed, is a more 

 confidcrable rrovcment than pitching ; but it is flow, and fcl- 

 dom attended with any accident. However, it (liould be 

 prevented as much as pofiible ; and this may be eafily done 

 in -rcneral, without any detriment to the iliip's ftifl" carrying 

 of fail, by ftowing up the ballaft, when it is iron, to the 

 floor-htads ; becaulc the fhip will be reflored by it with 

 lefs violence after ftic has inclined, and it will adl on a point 

 at a little diftance from the centre of gravity. 



B A L 



For the farther illuftration of this importatit fubjeft, let 

 it be premifed, thit various methods have been recommended 

 fur finding the following points of a ftiip ; viz. its centre 

 of gravity, centre ol cavity, centre of motion, and metacentrc. 

 (See thele articles.) Some of thefe points are fixed ; others 

 are variable. When a ih^p is completely loaded, the centre 

 of gravity is fixed, houfoevcr the veftel may alter her pofi- 

 tion. The centre of motion is always in a line with the 

 water's edge, when the Ctiitie of gravity is even with or 

 beiow the furface of the water; but, whenever the centre 

 of gravity is above the water's fuiface, the centre of gravity 

 is then the centre of motion. In circular bodies the centre 

 of motion will be the centre of the circle. The centre of 

 cavity vaiies with every inclination of the ftiip, becaufe that 

 depends npon tue ftiape of the body immerfeii. The mcta- 

 centre, called the ftiiftir.g centre, depends upon tht ftuation 

 of the centre of cavity ; fur it is that point where a vertical 

 line drawn from the centre ol cav ty crts a line palling 

 through the centre of gravity and perpendicular to the keel. 

 I'he centre of gravity muft not by any means be placed 

 abo^e this point ; becaufe, if that were the cafe, the veflel 

 would overfct. 



Let the fegment of a circle i 2 3 (fg. 14. Plate II. Me- 

 chanics), rcprefcnt the traniverfe (etlion ot a veftel's 

 bottom J W L the furface of the water ; M the mttacentre 

 as Well as the centre of motion, becaufe this is a circle ; C 

 the centre of cavity ; G the centre of gravity ; and the 

 line 2 4 the vertical axis of the vcffcl which may be turned 

 round the point M, as on a fulcrum, fupportcd by the ci ntrc 

 cf cavity. By thus fimply cnnfidcring the veflcl as a levtr 

 in the direftion of her vertical axis playing round her centre 

 cf m.otion, it is plain, that if the centre of gravity was 

 placed above the po'nt M, being the metactntre too, the 

 veftcl would upfet ; therefore that the fliip may have ftabi- 

 lity, the centre of gravity muft be below this point : and it 

 may be obfcrved, that the farther G is removed from the 

 mctacentre, the greater mull be its force, as the gravity 

 then adls with a g eater length of lever, conlidermg 'he 

 fulcrum of that lever to be at the centre of nol'on ; rr, if the 

 weight at G be augmented, it will likewife incrtaf. tl e forte ; 

 therefore the force of G may be exp'efled, bv multiply- 

 ing the balance of weight beneath the centre of motion, by 

 the diftance of the centre of gravity from the centre of mo- 

 tion. 



The centres of cavity and motion (in circular bodies) 

 will ever be in a line perpendicular to the horizon, but the 

 centre of gravity may be either on one iide or the other of 

 this line. When luch a body is at reft, the centre of gravity 

 will be in this Une ; but if in motion it will be diverted front 

 it. Thus the points M and C, will always be perpendicular 

 to W L ; but the point G, by the body's rolling, may be 

 on either fide ; for inftance at g. While G is perpendicu- 

 larly beneath the centre of motion, its a£lion can only tend 

 to prejer-ue this circular body in her ereft pofition ; but if 

 it is removed to either fide as to g., its aftion is to return it 

 to the ercfl pofition ; and thisaftion increafes as the diftance 

 G g, which is the fine of the angle of roll j' M O, the diftance 

 M G being confidered as the radius. Thu', to g^in the force 

 of gravity with any roll as g M G, let the balance of weight 

 beneath the centre of motion be multiplied by the fine of 

 the angle of roll G g. 



But the tendency to roll may be alfo diminiftied by the 

 ftiape of the hull : for, let us fuppofe that the tranfverfe 

 feftion be allowed more beam, and increafed by the dotted 

 lines. Now when this veffel is rolled over, it is plain that 

 the cavity will be augmented towards the fide L, of courfe 



its 



