Newton's Law: Its Application for Expressing Heat Losses from Homeotherms

Abstract

The applicability of Newton's law of cooling as a means of expressing heat losses from homeothermic animals has geen discussed at length in recent literature (Kleiber 1961, McNab 1970, Strunk 1971). Although this law has been used extensively (Scholander et al. 1950, Tucker 1965, Dawson and Schmidt-Nielson 1966, Herried and Kessel 1967, McNab 1966, Henshaw 1968), the relationship between Newton's original law and the Newton's law used by biologists today is at best remote (Strunk 1971, Kleiber 1961). Strunk (1971) has argued against the use of Newton's law as a biological model in favor of models that are based on the physical principles of heat loss from animals. McNab (1970) states that simple biological variability makes impractical the use of the more mechanistically correct equations, and Newton's law is perhaps a good pragmatic approach for expressing heat loss from homeotherms. This paper reports a theoretical examination of some similarities and differences between Newton's law and the thermodynamic energy balance as they have been used to describe heat losses from homeothermic animals in artificial and natural environments.