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Newton's law of cooling states that ''the rate of heat loss of a body is proportional to the difference in temperatures between the body and its surroundings while under the effects of a breeze.'' As such, it is equivalent to a statement that the heat transfer coefficient, which mediates between heat losses and temperature differences, is a constant. This condition is generally true in thermal conduction (where it is guaranteed by Fourier's law), but it is often only approximately true in conditions of convective heat transfer, where a number of physical processes make effective heat transfer coefficents somewhat dependent on temperature differences. Finally, in the case of heat transfer by thermal radiation, Newton's law of cooling is not true. Isaac Newton did not originally state his law in the above form in 1701, when it was originally formulated. Rather, using today's terms, Newton noted after some mathematical manipulation that ''the rate of temperature change'' of a body is proportional to the difference in temperatures between the body and its surroundings. This final simplest version of the law given by Newton himself, was partly due to confusion in Newton's time between the concepts of heat and temperature, which would not be fully disentangled until much later.〔(History of Newton's cooling law )〕 When stated in terms of temperature differences, Newton's law (with several further simplifying assumptions, such as a low Biot number and temperature-independent heat capacity) results in a simple differential equation for temperature-difference as a function of time. This equation has a solution that specifies a simple negative exponential rate of temperature-difference decrease, over time. This characteristic time function for temperature-difference behavior, is also associated with Newton's law of cooling. == Relationship to mechanism of cooling== Convection-cooling is sometimes called "Newton's law of cooling." This use is based on a work by Isaac Newton published anonymously as "Scala graduum Caloris. Calorum Descriptiones & signa." in ''Philosophical Transactions'', 1701,〔(824 )–829; ed. Joannes Nichols, ''Isaaci Newtoni Opera quae exstant omnia'', vol. 4 (1782), (403 )–407.〕 In cases where the heat transfer coefficient is independent, or relatively independent, of the temperature difference between object and environment, Newton's law is followed. This independence is sometimes the case, but is not guaranteed to be so. The heat transfer coefficient is often relatively independent of temperature in purely conduction-type cooling, but becomes a function of the temperature in classical natural convective heat transfer. In this case, Newton's law only approximates the result when the temperature changes are relatively small. Newton himself realized this limitation. A correction to Newton's law concerning larger temperature differentials was made in 1817 by Dulong and Petit. (These men are better-known for their formulation of the Dulong–Petit law concerning the molar specific heat capacity of a crystal.) Another situation with temperature-dependent transfer coefficient is radiative heat transfer. Newton's law is not followed here. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Newton's law of cooling」の詳細全文を読む スポンサード リンク
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