CHANGES OF QUANTITY. 239 



kalies and most of the salts. No man could, there- 

 fore, though he could gauge all the seas and lakes, 

 measure all the rivers and streams, and weigh all 

 the clouds, venture to give even an approximate 

 estimate of the quantity of water and its elements, 

 even for one time. 



The seasonal changes of it are also consider- 

 able. In England, it is in fogs and fens in the 

 winter, and in the crops on the fields, and the 

 leaves, flowers, and fruits of other annual and 

 deciduous vegetables, in the summer. In cli- 

 mates farther to the north, it is during winter 

 piled up in snow and ice : and in summer, it is 

 either at work in the more scanty vegetation, or 

 it has ebbed away to the ocean in the spring 

 " freshes " and floods. The action of gravitation 

 distributes it equally in the ocean ; and when it 

 rises in vapour, the action of heat disperses it in 

 the atmosphere. 



What these causes may, from time to time, 

 produce, we cannot calculate ; but within a very 

 long period of duration one as long at least as 

 we have any thing like authentic information, it 

 does not appear that the great collected quantity 

 has varied much. Now, according to the esti- 

 mates, which on such a subject must be vague, if 

 the solid parts of the earth those parts that we 

 have denominated land in distinction from water 

 were in the form of a regular spheroid, the form 

 which gravity, and the revolution and rotation of 

 the earth (the only external causes that we know, 

 that could act upon principles that we understand 

 in moulding the earth into its form), the water 

 would cover it with a crust, (if the term may be 

 used) or shell of water, something about two 



