98 



Prof. Tyndall on the Absorption and Radiation 



venieuce I have called the radiation and absorption of a gas or 

 vapour thus dynamically heated and cooled, dynamic radiation 

 and dynamic absorption. 



In illustration of the manner in which dynamic radiation may 

 be applied in researches on radiant heat, I have had made, 

 during the last half-year, a considerable number of experiments, 

 some of which I will here describe. In the first place, the expe- 

 rimental tube was divided iuto two compartments, as in the 

 experiments described in the foregoing section. The source of 

 heat was abolished, and one end of the experimental tube was 

 stopped by a plate of polished metal ; the other end was stopped 

 by a transparent plate of rock-salt, while the space between the 

 ends was divided into two compartments by a second plate of 

 rock-salt. The thermo-electric pile occupied its usual position 

 at the end of the tube, the compensating cube, however, being 

 abandoned. Tor the sake of convenient reference, I will call the 

 compartment of the tube most distant from the pile the first 

 chamber, and that adjacent to the pile the second chamber. 

 An outline sketch of the arrangement is given in fig. 3. 



Fig. 3. 



Jfad. Ckamb. 



MChaml. 



> 



^s 



The experiments were conducted in the following manner: — 

 Both compartments being exhausted and the needle at zero, the 

 gas was allowed to enter the first chamber through a gauge- 

 cock which made its time of entry 40 seconds. The second 

 chamber was preserved a vacuum ; the gas on entering the first 

 chamber was dynamically heated, and radiated its heat to the 

 pile through the vacuous second chamber; the needle moved, 

 and the limit of its excursion was noted. The first chamber 

 was then exhausted and carefully cleansed with dry air. The 

 second chamber was filled with the same gas, not with a view to 

 determine its dynamic radiation, but to examine its effect upon 

 the heat radiated from the first chamber. The needle being at 



