R. 



RAD 



RACOON, in Geography, a townfliip of Gallia county, 

 ill Ohio, having 295 inhabitants. 

 RADIATION of Heat, a property of heat or cir- 

 cumilancc belonging to it, which has been lately invefti- 

 gated and fuccel'sfnlly ilhillrated by profefTor Leflie of 

 Edinburgh. There are two modes in which heat is dif- 

 chargcd from bodies. A portion is communicated to the 

 contiguous matter, and is llowly diffufed through it. 

 Another portion, when the body is placed in an aerial 

 medium, is difchargcd with rapidity, darts through the air 

 to a diftance, and even at that diftance, when intercepted, 

 produces a heating effeft. This forms what is called the 

 " radiation of heat." Mr. Ledie has difcovered the 

 important faft, that different kinds of matter, at the fame 

 temperature, difcharge very different quantities of heat by 

 radiation. From a metallic furface, the quantity is compa- 

 ratively fmall ; from a vitreous furface, it is much greater ; 

 and it is Hill more fo from a rough fpongy furface. 



The power of different furfaces in difcharging different 

 portions of heat, in this mode, at the fame temperature, 

 Mr. Leflie afcribes to the more or lefs clofe contaft which 

 they admit with the external air ; a vitreous furface, for 

 example, admitting of a clofer proximity of the air than 

 a metallic furface does, and thereby communicating to it, 

 in a given time, a larger portion of heat. And on the 

 fame principle he explains the faft, that thofe furfaces 

 which are moll powerful in thus difcharging heat, are 

 alfo moll powerful in arrefting and abforbing it ; the 

 clofer contadl into which the heated air comes v\ itli the 

 furface on which it impinges, favouring the transfer of 

 its heat ; while a furface, to which the heated air does not 

 approach fo clofely, will in a great meafure reflctl it with 

 little lofs of heat. Hence the difcharging and abforbing 

 power are proportional to each other ; while the refledling 

 power is the revcrfe. 



Some important praclical applications refulting from thefe 

 differences are fuggcfted by the author. 



A veffcl with a bright metallic furface is the beft fitted 

 to preferve liquors either long warm, or as a confervatory 

 to keep them cool. A filvcr pot will emit fcarcely half 

 as much heat as one of porcelain ; and even the very 

 (lighten varnifhing of gold, platina, or fdver, which com- 

 municates to the ware a certain metallic glofs, renders this 

 new kind of manufafture about one-third part more 

 retentive of heat. The addition of a covering of flannel 

 though indeed a flow conduftor, far from checking the 

 diflipation of heat, has direttly the contrary tendency ; for 

 it prefents to the atmofphcre a furface of much greater 

 propulfive energy, which it would require a thicknefs of 



RAM 



not fewer than three folds of this loofe fubllance fully to 

 counterbalance. The cylinder of the fteam-engine has 

 lately been mofl advantageoufly flieathed with poliflied 

 copper. 



The progrefs of cooling is yet more retarded, by fur- 

 rounding the heated veffel, on all fides, at the diftance of 

 near an inch, with a cafe of planiflied tin ; and the addition 

 of other cafes, following at like intervals, augments con- 

 tinually the effeft. With an obilruclion of one cafe, the 

 rate of refrigeration is three times flower, with two cafes it 

 is five times flower, with three cafes it is feven times 

 flower, and fo forth, as expreffed by the fucceflion of the 

 odd numbers. By multiplying the metallic cafes, therefore, 

 and difpofing them like a neft at regular intervals, the 

 innermoil could be made to retain the fame temperature with 

 little variation for many hours or even days. Such an 

 apparatus would obvioufly be well calculated for various 

 culinary and domeftic purpofes. 



In the conveyance of heat by means of fteani, the furface 

 of the condufting tubes fhould have a metallic luftre. On 

 the contrary, if it be intended by that mode to warm an 

 apartment, they fhould be coated on the outfide with foft 

 paint, to facilitate their difcharge of heat. For the fame 

 reafon, metallic pots are more eafily heated on the fire, after 

 their bottoms have become taniiflied or fmokcd. If a 

 bright furface of metal be flightly furrowed or divided by 

 fine flutings, it will emit heat lenfibly fafter, becaufe the 

 prominent ridges, thus brought clofer to the general atmo- 

 fpheric boundary, will excite the pulfations with augmented 

 energy. 



For the experiments which led to this difcovery, and the 

 conclufions deduced from it, we refer to his " Effay on 

 Heat," and to a " Short Account of Experiments and Inilru- 

 ments depending on the Relations of Air to Heat and 

 Moifture." 8vo. Edinb. 1814. See Heat. See alfo Dew, 

 Rays of Heat, and Refrangibility of Radiant Heat. 



RADNOR, in Geography, a townfliip of Ohio, in Dela- 

 ware county, having ^7 perfons. 



RAJAPOOT, denotes literally the fon of a king, and 

 is ufed as the name of a warlike race of Hindoos. 



RAIN. For Inverary r. Inverarie. 



RAIN-GAGE, 1. 4, for LXIV. /•. XVI. ; for fg. 2. 

 r. 10. 



RALEGH, col. 5, 1. 20, /-. 1601. 



RAM of M. Montgolfier. Add— See Water. 



RAMA, or Ramah. Add — This was a common name 

 applied to many places in the Holy Land : and it is fug- 

 gelled (fee Clarke's Travels, vol. iv. p. 432.), that the 

 modern village of Bethoor and the modern Rama are the 



places 



