Applications of the Formulas 93 



ature of 74.8. The time employed by a particle of the liquid in 

 traversing the entire length of the pipe was eight and one-half 

 hours. The liquid when motionless cooled 9.9 in seven hours. 

 It is probable that the transmission is proportional to the excess 

 of the temperature of the pipe above 32, and for steam would 

 be between 75 and 100 B. T. U. 



INFLUENCE OF THE VARIATIONS OF EXTERIOR TEMPERATURE 

 ON THE QUANTITY OF HEAT TRANSMITTED THROUGH WALLS 



902. In what we have said regarding the transmission of 

 heat through bodies of low conductivity, we have supposed the 

 regime to have been established, and consequently that the inter- 

 ior and exterior temperatures were constant ; ordinarily the heat- 

 ing is regulated so that the interior temperature does not change, 

 but the transmission is always affected by the variations of exter- 

 ior temperature. These variations are of two sorts ; the general 

 decrease and increase of the mean exterior temperature during 

 the season of heating, and the accidental variations which mani- 

 fest themselves almost every day. We will examine the influence 

 of these two in turn. 



In our climate, * heating generally is necessary from the first 

 of October to the end of April, and during these seven months, 

 the mean exterior temperatures, deduced from the records of ten 

 years, are 

 Oct. Nov. Dec Jan. Feb. Mar. Apr. 



5i-8 45-i 37-4 36-1 39-7 43-9 5.9 



If we assume that the interior temperature is maintained at 

 59, that the walls are all exposed to the outer air, and that their 

 thickness is 39.37", the total quantity of heat transmitted per 

 square foot during the total duration of the heating, admitting 

 that the regime is constantly established would be (871) ; 



2.59X210X24=13050 #. 7". U. f 

 and the total heat above 32 contained in the wall at 59; 



3.28X62 4 X 2. 2X0.2 X 27 = 2430. 



This last quantity being less than two-tenths of the first, and 

 the cooling of the wall being never complete, it is easy to see that 

 if the variations of temperature took place gradually, without 



*Paris, France. 



fThe average exterior temperature for the seven months is here taken as 42.8 



