Heartwood

( Bot. ) The English term for DURAMEN, (q. v.) It is the central part of the trunk of a tree hardened by the deposition in its ti ue of various secretions which clog up the pa ages, and forbid the pa age of anything through them. Heart'-wounded, a. Wounded with love or sorrow; deeply moved or affected with some engro ing pa ion. Hearty, (härt'i,) a. Having the heart engaged in anything; sincere; warm; ardent; zealous; cordial; real; unfeigned; earnest; energetic; as, a hearty support; a hearty reception; a hearty shake of the hands, . In full health; robust; strong; vigorous; hale; sound-bodied durable; as, a hearty man, a hearty laugh. - Producing or promoting strength; invigorating: nourishing, as food; abundant in quantity; having a keen appetite; as, a hearty dinner, a hearty digestion, a hearty meal. A hearty eater, one who eats largely and heartily; one who plies his knife and fork well; a good feeder. Heat, ( het ,) n. [A.S. hatu, hato; L. Ger. and D. hitte; Ger. hitze ; Dan. hede; Icel. hit a, hit i; Goth. heito , a fever, akin to Gr. aitho , to burn or blaze, to Ar. hara rat , heat, and to Hind. hurûrut , heat.] The sensation caused by the approach or contact of a hot body, and the cause of that sensation. (See below, Physics.) "Great heats will follow, and large crops of grain." -Dryden. -Indication or effects of high temperature; high color of the face or body; redne ; flush; efflorescence; as, a white heat , a sparkling heat , a blood-red heat . "It has raised... heats in their faces." -Add is on. -State of being once hot or incandescent; exposure to heat; as, to give a bar of steel another heat . A violent action unintermitted; a course at a race; a single effort in running; as, three heats and a distance. "In the last heat , plain dealing won the race.' -Dryden. -Violent action or agitation of the system; utmost violence; rage; vehemence; ardor; agitation of mind; inflammation or excitement; exasperation; party spirit; as, the heat of pa ion, the heat of play, the heat of the moment, . "We have spilt no blood but on the heat of the battle." -Atterbury. -Fervency; animation in thought or discourse; ardor of expre ion or elocution. "Plead it to her with all the strength and heat of eloquence." Add is on. -Fermentation; effervescence. Blood- heat , the natural temperature of the human body, or about 98° Fahr. IMG:content-0546.png:[blocks in formation] Refrigerators and fire-proof safes are constructed with double sides, and the space between them is filled with some non-conductor of heat, as alum, charcoal, or plaster of Paris. Liquids and gases are almost perfect non-conductors of H. Water may be boiled in the upper part of a tube over ice without melting the ice, and if a quantity of alcohol be inflamed on the surface of water, the water will not be warmed below the surface. Common air is almost an absolute non-conductor. The air retained in the meshes and between the layers of clothing prevents the heat of the body from being conducted away, and thus keeps us warm. The same substance that proves the best defence against the cold also protects the body from the effects of great external heat. Workmen and firemen exposed to intense heat protect themselves by woollen garments, and we wrap ice in flannel to keep it from the heated air without. Double doors and windows render apartments warmer by enclosing a quantity of air which does not convey away the heat as readily as the solid walls. - Liquids and gases are heated by convection. If H. be applied to the surface of a liquid, we have seen that the lower portions remain unaffected by it. If the heat, however, be applied to the lower part of a ve el containing a liquid or gas, the heated particles become expanded, and rising, give place to colder ones, which are heated in their turn. In this manner all portions of the liquid are heated alike. Fig. 1258 illustrates how the heat applied to the bottom of a ve el of water is diffused through the whole ma . It will be seen that two sets of currents are established, the hot particles rising to the top, and the cold ones sinking to the bottom. On the same principle the air of a room is warmed, and for this reason the heat should en Fig . 1258. ter the apartment as near the floor as po ible. Liquids and gases cool from the surface; as the particles become cold they contract and sink, while warmer ones rise and take their places. Thick liquids, as soup, oils, mola es, tar, ., retain their heat longer, since their particles do not so readily move among themselves on account of their greater cohesion. - Radiation of H. By this is understood the pa age of H. from one body to another, either through a vacuum, the air, or even through a solid. Prof. Tyndall defines radiation as "the communication of motion from the particles of a heated body to the ether in which these bodies are immersed." Substances differ very much in their power of emitting H. , and the radiating power of the same body varies greatly, according to the nature of its surface. Highly polished surfaces are poor radiators, while dark, dull bodies are generally good radiators. It is proved, however, that color alone has no effect on radiation. If a metallic cube, having its sides coated with different coloring-matters, be filled with hot water, it will be found that the radiation from each will be the same. Ve els designed to retain the heat of their contents should have clean, polished surfaces, while stoves, or bodies intended to impart H. , should be somewhat rough, or not highly polished. Radiant H. is thrown off in straight lines, and is reflected, absorbed, transmitted, and refracted, in obedience to the same laws that govern light. It is also susceptible of polarization. That it is reflected, may be proved by placing a hot ball of iron in the focus of a concave reflector, while some gunpowder is placed in the focus of a similar reflector, a number of feet distant from the ball. The powder will be ignited, though, placed at any other point much nearer the ball, it would remain unaffected. If we stand with our back to a bright fire, and hold a mirror in such position that we may see its reflected light, the face receives at the same time the sensation of heat. By an arrangement of mirrors, Arch i me des, in his famous defence of Syracuse, was enabled to fire the fleet of Mar cell us by the concentrated and reflected heat of the sun's rays. Radiant heat is absorbed readily by surfaces that are good radiators, and but imperfectly by those surfaces that are good reflectors. Dark, rough bodies absorb readily and become sooner heated than smooth and polished ones; for instance, water is sooner heated in a kettle whose outside is covered with soot, than in one that is bright and clean. In the experiment above described, with the hot ball, the mirror is not heated, though within a few inches of the hot iron, so perfectly does its polished surface reflect the rays of heat. The air is a poor abBorber of H. The sun's rays pa through it without sensibly increasing its temperature; and it becomes warmed principally by convection from the heated surface of the earth. The sun's heat pa es thiough the air and transparent bodies without lo , but heat from other sources is more or le absorbed by bodies that allow light to pa readily through them. Bodies allowing a free pa age of H. through them are called dia therm a no us , and those that absorb the most of the H. they receive are called athermanous. Rock-salt and air transmit the rays from sources of heat of all kinds, but all other bodies absorb a portion of the heat-rays in the same manner that colored gla es intercept or absorb some of the rays of light. The facts in this connection are very remarkable; we can give space for but few. If we take, as a source of heat, a kettle filled with boiling water, a thin plate of transparent rock-salt will transmit 92 out of 100 rays, while rock-crystal, plategla , transparent alum, and clear ice, all of the same thickne , will not transmit any. With the exception of rock-salt, the transmi ive power of different bodies varies with the quality of the heat, and it differs in the same body with the intensity of the heat. Thus, plate glase which transmits none of the heat from a copper ball heated to 2120, transmits 6 per cent. of that from the same ball at a temperature of 750°. The facts of radiation and absorption afford an explanation of the interesting phenomena of DEW (q. v.), of frost which is frozen dew, of land and sea breezes, and of winds. (See WINDS.)- H. tends to diffuse itself until all neighboring bodies have acquired a uniform temperature. If a hot ball of iron be placed in a room, it parts with its heat until the objects in the room and itself have the same temperature. If a block of ice at 320 be introduced into a room having a temperature lower than its own, it radiates H. , and thus warms or elevates the temperature of the room.- Latent H. Whenever a solid is changed into a liquid, a certain amount of heat disap pears, or becomes insensible to the thermometer. To melt ice at 32° requires 143 degrees of heat, and yet the water produced has a temperature of only 320. The latent H. of water is then said to be 143°, and this amount of heat reappears when it is re-frozen. A similar effect is produced when a solid or liquid is changed to a vapor or gas. To change water at 2120 into steam of the same temperature, 067 degrees of H. are required. The latent heat of steam, then, is 967°, which becomes sensible, or reappears on its condensation into water. Cold is produced when solids are liquefied by slow empty end plunged into a freezing mixture, as ice and