28o THE POPULAR SCIENCE MONTHLY. 



ON GEOUND-AIR m ITS HYGIENIC RELATIONS.' 



Br De. ALtVX von PETTENKOFER, 



PEOFESSOK OF HYGIE>'E IN TUE LTSlVEESITy OF MUNICH. 



IF in the two preceding lectures I have tried to draw your attention 

 to the penetration of the air into our clotliing and our dwellings, 

 I shall try in this last lecture to do the same in reference to the air 

 which is in the ground, and to its connection and intercourse with the 

 air above the ground. The air in the ground has been somewhat a 

 stranger to our minds; the terms air and earth, just like air and 

 water, implied to our mind things contrary, and exclusive of each 

 other. The earth seemed to have its limit where the air began. 

 Common-sense seems inclined to believe that there can be no air in 

 that whereon we walk and stand. If we say of the surface of the 

 earth that it is the limit of the earth and the beginning of the atmos- 

 phere, we are not correct in reference to the latter. The air begins 

 much below the ground, and we ought to say that where the ground, 

 which is a mixture of earth, water, and air, ends, from there the at- 

 mosphere exists alone. It is no wonder that no particular attention 

 was paid to the air in the soil ; its presence there does not make any 

 direct impression on anyone of our senses; we infer its presence 

 more from otlier experiences and consequent conclusions. The human 

 mind formerly looked upon the air as something unsubstantial, spir- 

 itual, although men saw the effect of hurricanes ; no wonder, then, 

 that no one thought of the air hidden in the ground, which cannot 

 even blow the hat from our head. 



We again meet here with the fact that, originally, only that calls 

 forth ideas which impresses our senses directly. No one doubts that 

 water penetrates the soil, and moves there according to hydrostatic 

 laws, because we see it run, vanish into the soil, collect and run out 

 again, or we pump it up ; but hitherto not many have clearly undei*- 

 stood that the whole surface of the earth, as far as it is porous and 

 its pores are not filled with -water, contains air, which is also subject 

 to aerostatic laws. And why so ? One feels nothing of that air ; it is 

 always calm, it has no color, no smell, no taste, in fact we take it for 

 nothing, I have shown you already how great an error we commit 

 when we suppose a calm air to be motionless. This applies just as 

 much to the air in the soil, wliich, if its motion were even snail-like, 

 would still travel from a good depth to the surface in one day. 



Perhaps I shall succeed in giving you a better idea of the change 

 of the air in the ground than of that in walls. To have a correct idea 



' Abridged and translated by Augustus Hess, M. D., member of the Royal College of 

 Physicians, London. 



