4 Dr. Carpenter on Hard Water. 
the chalk hills in this neighbourhood far above the present 
level of the sea. When new land was thus thrown up, it 
immediately became liable to be worn away again by air and 
water, and carried back into the sea; so that nature might be 
said to keep up a constant system of change on the face of 
the globe. The main object, however, of his paper was to 
point out that nature did not leave man unprotected from his 
own acts. He might foul his supply of drinking water, but 
Providence turned the ammonia compounds into nitrates and 
nitrides, and prevented a carbonic acid atmosphere in the under- 
ground air by providing an abundance of lime. The under- 
ground air is purified by it in those places in which vegetation 
does not take up the carbonic acid, and thus the spread of such 
diseases as typhoid by drinking water is limited, Dr. Carpenter 
contending that typhoid germs cannot vegetate in the absence 
of carbonic acid. 
