ON THE AIR ANDRATN OP MANCHESTER. 209 



sulphureous, and aqueous salts." Here, however, is brought 

 prominently forward an opinion of long standing, the mix- 

 ture of solids with the air, giving rise to the expressions, 

 "lighter and denser," "moist and earthy," "mixed with the 

 exhalations of the earth." " Terreni halitu miscens" are 

 Pliny's words. 



Des Cartes found it necessary, therefore, to give a more 

 minute description of air : " We know that air can be no- 

 thing but a collection of particles of the third element — that 

 it is a fluid very rare and pellucid," distinctly bringing it 

 under the class of ordinary material bodies, and taking it from 

 the sphere of mind. 



The great difference of difi'erent airs, and the effect they 

 have in the system in raising or depressing the spirits, have no 

 doubt been causes why air should have had many indefinite 

 notions connected with it, independent of the ordinary want of 

 a correct definition of matter, and the peculiar difficulties 

 in the case of a body which cannot be seen. When a person 

 is depressed in one place, and elevated in another, he is not 

 unwilling to believe the very poetical idea of Heraditus that 

 " we receive our life by breathing in the air the soul of the 

 world." And to a great extent there is a practical truth in 

 this, as we are often found to possess more or less life accord- 

 ing to the condition of the air. 



Modern chemistry has gone far towards proving the correct- 

 ness of ancient impressions, that the air goes with the blood 

 through the whole body, and some have almost gone as far 

 as a Greek philosopher, who said that " the soul is in the 

 lungs." 



As so many opinions have already been delivered on air, it 

 is not easy for any one to bring forward more beautiful or 

 more expansive ones ; there is room, however, for experi- 

 ments to make our ideas more definite. We hear of pure 

 and impure air, but these phrases do not convey the same 

 meaning to all persons. Impure air is simply air with impu- 



2e 



