THE CHEMISTRY OF THE ATMOSPHERE. 103 



learned in Part I, Chapter XIV., he found that the yellow 

 ray is that portion which is the peculiar stimulus of the 

 chemistry of the leaves. 



130. Priestley's Experiment. This chemical action of the 

 leaves was first demonstrated by Priestley, the discoverer 

 of oxygen (48). The exper- 

 iment by which he demon- 

 strated it is represented in 



Fig. 32. Some green leaves 

 were placed in a bell-jar filled 

 with water well charged with 

 carbonic anhydride, and the 

 bell-jar was then inverted, as 

 you see, in a vessel of water. 

 Placing the apparatus in the Fig. 32. 



sun, he saw bubbles of gas arise continually from the sur- 

 face of the leaves, and soon quite a quantity of this gas was 

 collected in the upper part of the bell-jar, forcing of course 

 a part of the water downward. This gas, on being tested, 

 was found to be oxygen, and an examination of the water 

 showed that the carbonic anhydride in it had disappeared. 

 The conclusion was clear, then, that the leaves had absorbed 

 carbonic anhydride, and at the same time had given out 

 oxygen. 



131. Wonderful Balancing of the Chemistry of the Atmos- 

 phere. Free air, we have told you, is everywhere composed 

 of its three ingredients in the same proportions. Climate 

 makes no difference. A gallon of air taken from the torrid 

 zone, where the rank vegetation is breathing out such quan- 

 tities of carbonic anhydride, and taking in from the air so 

 much of its oxygen, on being examined by the chemist, 

 shows the same proportions of nitrogen, oxygen, and car- 

 bonic anhydride that a gallon of air does which has been 

 taken from the icy regions of the North, where all vegeta- 



