32 Emission and Transmission of Heat 



values of rates of cooling, can not be made simple on thermome- 

 ters. I have used spheres of thin brass with diameters ranging 

 from two inches to twelve inches, a number of cylinders with 

 diameters of one and a quarter inches to twelve inches and 

 lengths of two to twenty inches, and also several rectangular 

 vessels of different dimensions. 



All of these vessels have been employed successively bare 

 and covered with different substances. The water which they 

 contained was continuously agitated. The temperatures were 

 measured by very sensitive thermometers. Intervals of time 

 were determined by means of a Breguet counter. 



The vessels were placed in an open chamber having a double 

 wall. The interval between the walls was filled with water, and 

 the contained air was constantly renewed through passages 

 which gave to the entering air the temperature of the walls of 

 the chamber. 



782. Figure 149 represents a vertical section of the constant 

 temperature chamber, figure 150 a plain of the same. ABCDEF 

 and A' B' CHEF are two cylinders of sheet iron plated with 

 lead. They are concentric and the intervening space is filled 

 with water. 



This envelope is formed of two halves separated in a vertical 

 plane and held together by suitable fastenings. The interior cyl- 

 inder is 39 inches high, and 32 inches in diameter ; the interval 

 between the two cylinders is i ^ inches and the water contained 

 in this interval is frequently agitated by horizontal annular 

 plates, to which are attached vertical iron rods projecting 

 through the little stuffing boxes GG. 



The temperatures of the water in each half of the envelope is 

 given by thermometers inserted at /and I. JfLMsmd K 1 L' M' are 

 two vertical enclosures fastened on the outside of each half of the 

 chamber. They are open above and communicate below with the 

 openings NP (fig. 149) fashioned in the lower part of each of the 

 two halves of the chamber. The outer wall of these enclosures 

 is made of wood. They contain throughout their height, strips 

 of sheet iron soldered perpendicular onto the outer surface of 

 the chamber, each 4 inches high, and extending to the wooden 

 outside of the enclosure, and the strips of one horizontal row are 



