HAR
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meet D k; with the same distance describe a third arc, ofcontrary curvature, and draw a vertical line to touch itj thuswill one side of the section of the rail be formed. Thecounter-part is formed by a similar operation.
Figure 3 is the most simple form for the section of a rail,being that of a circle.
To describe the mitre-cap of a rail.
Figure 4.—Describe a circle, a eb d, to the intended sizefthe proportion here between the rail and the cap is as 2 to3 ) ; draw the diameters a b and e d at right angles; producee d, and place the middle of the section of the rail upon e d;draw b Q to touch the section of the rail, and to cut the circlea e b d in Q ; draw the side PQ of the mitre ; draw A b tomeet the points of contact, A and B, of the lines parallelto e d, which are tangents to the section. Then to find anypoint in the curve of the section of the mitre-cap : let G bea point in the section of the rail; draw g k, meeting p q ink ; from the centre of the circle aeb d, describe an arc, k f,meeting a b in f; from the point of section f draw f g, per-pendicular to a b ; and make f g equal to F G.
All other points are found in the same manner ; or a seriesof lines may be drawn from any number of assumed pointsin the section, and lines parallel to ed, drawn from them tocut p Q; arcs may then be described from each point of sec-tion to meet a b, and perpendiculars drawn from the pointsof section in a b; all these perpendiculars should be madeequal to the respective ordinates of the section, and a curvedrawn through their extremities will form the curve of themitre-cap.
HANGING, of doors, or shutters, the act of placing themupon centres or hinges, for the convenience of opening andshutting. See Hinging.
Hanging Style, the style of a door or shutter, to whichthe hinge is fastened.
The terra is also applied to a narrow style fixed to thejamb, on which the door or shutter is sometimes hung. Inthis case the hanging style is used with the view of makingthe shutter or door revolve more than a right angle, in orderto turn it into a given position ; as to bring a door close toa partition, to keep it out of the way.
HANGINGS, linings for rooms, made of arris, tapestry,or the like.
HANGS OYER, an expression used in speaking of a wall,when the top projects beyond the bottom.
HARD BODIES, such bodies as are absolutely inflexibleto any shock or collision whatever.
This is the common meaning of the term : but Huygens ,by hard bodies ( corpora dura ) meant what others callperfectly elastic bodies ; for he thus expresses himself:“ Quascunque sit causa, corporibus duris, a mutuo contacturesiliendi cum se invicem impinguntur : ponimus, cum cor-pora duo inter se aequalia, aequali celeritate, ex adverso acdirecte sibi mutuo occurrent, resilire utrumque eadem quaadvenit celeritate.” Huyg. De Motu Corp. ex Percuss,ffypoth. 2. But this hypothesis is consistent only with per-fect elasticity, and not with the common supposition of hard-ness or inflexibility, which produces no resilition. The lawsof motion for hard bodies are the same as for soft bodies, andthese two sorts of bodies might be comprised under the com-mon name of unelastic.
Some who follow Leibnitz ’s doctrine, concerning the measurepf the moving force of bodies, deny the existence of hard or•nflexible bodies. And it is so far true, that no experiencee ver taught us that there are any such. The hardest bodiesto appearance do not preserve their figures in collision, suchIndies being only elastic, yielding to the shock, and thenRestoring themselves.
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M. Bernoulli goes so far as to say, that hardness, in thevulgar sense, is absolutely impossible, being contrary to thelaw of continuity. For supposing two such hard bodies ofequal masses, and with equal velocities, to meet directly, theymust either stop or return after the collision. The first sup-position is commonly admitted ; but then it follows, that thesebodies must instantaneously pass from motion to rest, withoutgoing through successive diminutions of their velocities tillthey stop : but this is thought to be contrary to the funda-mental laws of nature. Hence this author rejects perfectlysolid and inflexible atoms, which others think a consequenceof the impenetrability of matter.
Hard, a name given to a ford or passable place in a riverparticularly in and near the Fens, where many of theseformerly occurred, composed of gravel, probably broughtthither for the purpose. These Hards proved very detri- j jmental to navigation in dry seasons, and obstructed and aug-mented the floods in wet ones, until they were removed.Frequent mention is made of them by Mr. Smeaton, andby other writers on the navigation and drainage of thosedistricts.
Hard Finishing. See Plastering.
HARDENING OF TIMBER. See Timber.
HARMONIC or HARMONICAL PROPORTION, iswhen, in a series of quantities, any three adjoining termsbeing taken, the difference between the first and second is tothe difference between the second and third as the first is to j
the third. The reciprocals of a series of numbers in arith- j
metical progression are in harmonical proportion : thus the |
reciprocals J, &c. of 1, 2, 3, 4, &c., are in harmonical j
proportion ; also, the reciprocals &c., of 1, 3, 5, 7, j
&c. are harmonicals. i
HARMONY, an agreement between 11 the parts of a ibuilding ; the word is of similar import with Symmetry ,which see. j
HARNESS ROOM, a small apartment for keeping theharness in, that it may be preserved from mouldiness. Theharness-room should be perfectly dry, and placed as near thestable as possible.
HASP, a fastening; it is in form a small clasp that passesover a staple to be fastened by a padlock.
HATCH-WAY, an aperture through the ceiling, to afforda passage to the roof.
HATCHET (from the French hachette) a small axe , usedby joiners for reducing the edges of boards.
HAUNCH. That part of an arch between the vertex andthe springing.
HEAD (from the Saxon) an ornament of sculpture ofcarved work, frequently serving as the key of an arch orplatband.
These heads usually represent some of the heathen deities,virtues, seasons, or ages, with their attributes. The heads ofbeasts are also used in suitable places ; as a bullock’s or sheep’shead, for a shambles or market-house ; a dog’s, for a kennel;a deer’s or boar’s, for a park or forest; or a horse’s, for astable.
In the metopes for the friezes and other antique Doric temples, we meet with representations of bullocks’ or rams’heads flayed, as a symbol of the sacrifices offered there.
Head, Jerkin, See Jerkin Head.
HEADER. See Heading Course.
HEADING COURSE, in masonry, a course of stones in Iwhich their length is inserted in the thickness of the wall ;those with their length in the face of the wall are calledstretchers. The same is also to be understood of brickwork.
Heading Joint, in joinery, the joint of two or more boardsat right angles to the fibres; or, in hand-railin?, at right |