A X I 



wHl be the f.t.alleft of aU thofe able to fuftain tbe weiRht 

 W, according to the feveral paraUel lines of direc- 

 tion. 



4. If a power adin^ according to the pei-pendiciilar AL, 

 raife the weight W, the fpace pafTed through by the power 

 will be to the fpace paiTed through by the weight, as the 

 weight to the power which is able to fuftain it. 



For, in eacli revolution of the wheel, the power pafTes 

 through its whole periphery ; and in the fame time the 

 weight is raifed through an interval equal to the periphery 

 of the axis ; the fpace of the power therefore is to the fpace 

 of the weight, as the penpher)' of the wh^el to that of the 

 axis ; but the power is to the weight, as the radius of the 

 axis to that of the wheel. Therefore, &c. 



5. A power and a weight being given, to conftruft an 

 axis in peiitrochio, by which the weight {hall be fuftaincd 

 and raifed by the given power. Let the axis be large enough 

 to fupport the weight without breaking. Then, as the 

 weight is to the power, fo make the radius of the wheel, or 

 the length of the fpoke, to the radius of the axis. 



Hence, if the power be but a fmall part of the weight, 

 tlie radius of the wheel muft be vailly great. — E. gr. Sup- 

 pofe the weight 4050 and the power 50, the radius of the 

 wheel will be to that of the axis as 81 to f. But fuch a 

 machine would be of an incouvcnient fize ; and it may 

 therefore be provided againft by increafuig the number of 

 the wheels and axes ; and making one to turn round ano- 

 ther by means of teeth or pinions. 



To find the effeft of a number of wheels and axes, thus 

 turning one another, multiply together all the radii of the 

 axes, and all the radii of the wheels, and then it will be, as 

 the produdl of the former is to the produft of the latter, fo 

 is the power to the weight. Thus, if there be four wheels 

 and axes, the radius of each axis being one foot, and the radius 

 of each wheel b.'i,:g three feet ; then the continual produft of 

 all the radii of the wheels is 3 X 3 ^. ;? x 3, or Si feet, and that 

 of the radii of the axes only i ; confcquently the efftft is as 81 

 to I, or the wciglit may be 8 1 times the power. On the con- 

 trary, if it be required to find the diameter of each of four 

 equal wheels, by^which a weight of 4050 lb. fliall be ba- 

 lanced by a power of 50 lb. the diameter of each axis being 

 one foot ; divide 4050 by 50, and the quotient is 81 ; ex- 

 traft the fourth root of 81, or twice the fquare root, and 

 it will be 3, for the diameter of each of the four wheels 

 fought. See Wheels. See alfo Mechamical Powers. 



6. If P and W ?.&. in the fame plane, and in the di- 

 reftions PD and WD ('^g. 7. and 8.), meeting in D, and 

 be in equilibrio, they are equivalent to a third force, or 

 preflure upon the axis at A, wliofe direction meets PD and 

 W'D in D (fee Motion) ; and producing PD, WD, thefe 

 three forces are to each other, as the fides DF, DE, and 

 diagonal DG, -of the parallelogram EF ; confequently 

 P : W : : DF : DE, or drawing AN, AM, perpendi- 

 cular to WD and FDP refpeaively, P ; W : : AN : 

 AM. See Lever. 



7. The prefFure upon the axis at A (i. e. Pr) : P : : 

 DG : DF :: fin. /iDFG or PDAV : fin. .i.FGD or 

 ADW ; Pr : W : : DG : DE : : fin. Z.DEG or PDW 

 : fin. /LDGEorADP; and P : W : : fin. Z.ADW : 

 fin. Z.ADP. When the angle PDW is infinitely fmall, or 

 PD and WD are parallel, the perpendiculars AN, AM are 

 to each other as AW : PA. Parkinfon's Syllem of Me- 

 chanics, &c. p. 137. 



Axis of a Vejfd, is that quiefcent right line palling 

 through the middle thereof, perpendicularly to its bafe, and 

 equally dift^ant from its fides. 



Axis, in Optics. Optic ix'is, or vtfual axis, is a ray paf- 



A X I 



fing through the centre of the eye ; or it i^ that ray, which, 

 proceeding through the middle of the luminous cone, fall* 

 perpendicularly on the crjftallinc humour, and confequcntlr 

 pafles through the centre of tlie eye. 



Axis, Common, or Mean, is a right line drawn from the 

 point of concourfe of the two optic nerves, tlirough the 

 middle of the rig!;t Unc which joins the estrerr.itv of the 

 fame optic nerves. 



Axis of a Lens, or Ghfs, is a right line pafllnrr along 

 the axis of that foliJ, of which the lens is a fcgrr.cnl. 



Thus, a fpherical convex lens being a fegment of fome' 

 fphere, the axis of the lens is the fame witli the axis of the 

 fpFiere ; or it is a right line palTiiig through the centre thereof. 

 Or, the axis of a glafs is a right line joining the middle 

 points of the two oppofitc furfaces of the glafs. See 

 Lens. 



Axis of Incidince, in Dioptrics, is a right line drawn 

 through the point of ii;cidencc, perpendicularly to the re- 

 fiafting furface. See Incidexce. 



Axis of RefraSion, is a right line continued from the 

 point of incidence or refraction perpendicubriy to the re- 

 frafting furface, along the farther medium. Or, it is that 

 made by the incident ray, perpendicularly prolonged on the 

 fide of the fecond medium. See Refraction. 



Ax\i, m Zoology, a. fpecies of the Cervus, or Stas 

 genus, with branched, ro.md, creA horns, that are bifid at 

 the fummit ; and tlie body fpotted with white. Erxleb. 

 Mamm. p. 312. Schreber, &c. 



The axis, according to Sonnini and others, is an animal 

 almofi; peculiar to the colder parts of Afia ; it inhabits the 

 wooded mountains of the Celebes, Java, and Ceylon, in great 

 numbers, but it is ftill more abundant on the banks of the 

 river Ganges, and for that reafon is not unfrequently caUed 

 the Ganges flag. The axis multiplies fall in the parks and 

 menageries of England, France, and other parts of Europe ; 

 and being a moft graceful animal, is no fmall ornament to 

 the grounds of the nobility and gentry. It is faid to pro- 

 pagate with the female of the common ilag ; and it is 

 equally probable, that the female axis would produce with 

 the male of the other kind. 



This animal was known to the aneients by the name of 

 axis. Pliny fpeaks of it as a native of India, and inform* 

 us likewife that it was confecrated to Bacchus. Its Cze is 

 nearly that of the fallow deer ; colour above pale rufout 

 brown, elegantly fpotted with white, beneath white ; tail 

 hke that of the fallow deer, and rufous above, and white be- 

 neath. The axis is eafily tamed ; its fmell is exquifite ; and 

 flelh very good when faked. 



Gmelin, on the authority of Pennant, fpeaks of two va- 

 rieties of this creature ; the firft, with a body uniformly of 

 one colour, with the extremity of the horns trifurcattd ; 

 and the other with horns that are alfo trifurcated, but larger, 

 and whitilh. Thtfe are the miiuilc axis zwA fpAltd axis o^ 

 Dr. Shaw ; and are thus noticed in the Gen. Zool. of tljat 

 author. " Middle axis. Whether this be a variety of the 

 former (fpotted axis), or fpccifically dilUnft, does not appear 

 perfc£ily clear. It is, according to Mr. Pennant, of a mid- 

 dle fize between the fpotted axis and the great i:xij or fol- 

 lowing kind. In tiie colour of its hair, it refembles the 

 firft fort ; but is never fpotted. It, however, is faid to vary 

 into white, in which ftate it is confidercd as a great rarity. 

 It inhabits diy hilly forefts in Ceylon, Borneo, Celebes, and 

 Java, where it is found in ver\- numerous herds. Its flefh 

 is much efteemed by the natives, and is dried and falted for 

 ufe.'' — " Great Axis. The exillence of this fpecies, or vari- 

 ety, is afccrtained from a pair of horns in the Bricilh Mufeura, 

 refembling the former kinds in Ihape, but of a larger fize ; 

 3 E 2 they 



