OF PNEUMATICS. 203 



This enlivening quality in air, is also destroyed by LECT. 

 //if ur's passing through fire ; particularly charcoal ^[^^ 

 fire, or the flame of sulphur. Hence, smoking chim- 

 neys must be very unwholesome, especially if the rooms 

 they are in be small and close. 



Air is also vitiated, by remaining closely pent up in 

 any place for a considerable time ; or perhaps, by being 

 mixed with malignant steams and particles flowing from 

 the neighbouring bodies ; or lastly, by the corruption 

 of the vivifying spirit ; as in the holds of ships, in oil- 

 cisterns, or wine-cellars, which have been shut for a 

 considerable time. The air in many of them is some- 

 times so much vitiated, as to be immediate death to any 

 animal that comes into it. 



Air that has lost its vivifying spirit, is called damp, 

 not only because it is filled with humid or moist va- 

 pours, but because it deadens fire, extinguishes flame, 

 and destroys life. The dreadful effects of damps are 

 sufiiciently known to such as work in mines." 



If part of the vivifying spirit of air in any country 

 begins to putrify, the inhabitants of that country will be 

 subject to an epidemical disease, which will continue 

 .until the putrefaction is over. And as the putrefying 

 spirit occasions the disease, so if the diseased body 

 contributes towards the putrefying of the air, then the 

 disease will not only be epidemical, but pestilential and 

 contagious. 



The atmosphere is the common receptacle of all the 

 effluvia or vapours arising from different bodies ; of 

 the steams and smoke of things burnt or melted ; the 

 fogs or vapours proceeding from damp watery places ; 



3iote 56. We have stated that atmospheric air is a compound fluid, 

 and one of its constituents is in the preceding page not unaptly called 

 a vivifjing spirit, but by far the largest portion of the air we breathe 

 is destructive both of animal life and flame. The latter constituent is 

 called nitrogen ; and, in general, when we speak of an impure atmo- 

 sphere, we mean one exhausted of its vivifying principle. 



