CHAPTER IV. 



ATMOSPHERE OF THE CAVE. 



As the circulation of the air, its temperature, 

 purity, etc., in the Cave, are subjects upon which 

 we are frequently interrogated, and which pos- 

 sess great interest to all anticipating a visit, we 

 proceed to give the explanation of these points 

 in the words of Dr. Wright, who thus treats 

 of what he very properly terms the respiration 

 of the cave. « 



The Mammoth Cave breathes once a year. 

 That is to say, in summer, or when the tempera- 

 ture of the external air is above that of the 

 Cave, the current sets from the latter to the 

 former. In other words, the Cave is the entire 

 summer in making an expiration. On the other 

 hand, when the order is reversed, or the tem- 

 perature of the outer atmosphere is below fifty- 

 nine degrees, the Cave makes an inspiration, 

 or draws in its breath, which it accomplishes 

 during the winter. The respiratory mechanism 

 of the Cave ceases to operate — or, to carry out 



(43) 



