PROM WOOD AAli COAL. 3f> 



Numerous experiments have been made to determine tin 

 law which obtains in the cdbling of heated bodies. Although 

 my apparatus did not admit of making experiments on tin's 

 subject at high temperatures, yet it appears in one respect 

 better adapted for the purpose than any other which has. to my 

 knowledge, been made use <>f. as we are enabled to maintain 

 both the heated body and the refrigerating medium at the same 

 difference of temperature, for a sufficient period of time, to 

 determine the question with accuracy. My experiments con- 

 sisted in maintaining the temperature of the interior room 10 

 20°, 30°, and 40° above the temperature of the exterior mom 

 for the same period of time, and the quantity of fuel required 

 was found to be directly proportional to the increased diffe- 

 rence in temperature. These results are in agreement with 

 the assumption of Newton, the geometrical law of Richmann, 

 and also correspond at these differences of temperature with 

 the experiments of MM. Dulong and Petit, although the 

 latter gentlemen found very different results at higher tempo- 

 ral ores. 



The usual method which has been adopted to determine this 

 question, by finding the period which fluids require, when 

 heated, to cool through a given number of degrees in different 

 parts df the scale of a thermometer, appears liable to rami 

 objections, which it becomes inc. however, to notice with de- 

 ference. The shape or size of the containing vessel is aof 

 perhaps, material, lint as spheres have been most generally used. 

 my remarks will he confined to thai shape. 



We will, for illustration, assume thecontainingvessel t" be the 

 hulh of a thermometer two inches in diameter, and filled with 

 mercury. This we will suppose to he heated to i" 1 * "i Fahren- 

 heit, and placed in vacuo, in which case it is said to Insc its beat 

 by radiation only Now. a- the stratum of mercury in contact 

 with the bulb, parts with i1s heat, it contracts and occupies |< — 

 •pace in the hulh. which causes a portion of that within tin 



tube to sink into the hulh in order to supply the deficiency. 

 This e\teri.. i stratum must tin n he supposed, from its |,,s, ,.| 



heat, to have acquired gr< ater density, and t" \< ave 'he sides ol 



