SCIENCE OF COMMON THINGS. 169 



Why a dew-drop is round. AVhy a duck is not wet with water. 



Because every part of it is equally balanced ; and 

 therefore there is no cause why one part of the drop 

 should be farther from the centre than another. 



11O5 Why will dew-drops roll about cabbage plants, poppies, &c., with- 

 out wetting the surface ? 



Because the leaves of cabbages and poppies are 

 covered with a very fine waxen powder, over which the 

 dew-drop rolls without wetting the surface, as a drop of 

 rain would over dust. 



HO 6 Why does not a drop of rain wet the dust over which it rottsf 



Because dust has no affinity for w^ater, and therefore 

 repels it. 



HOT* Why can swans and ducks dive under water vnthout being wetted 1 



Because their feathers are covered with an oily secre- 

 tion, which has no affinity for water, and therefore re- 

 pels it. 



11O8 WJiat is tlie figure which water always assumes when unsupported, 

 or supported on a surface having little attraction for it? 



The figure of a sphere. This figure becomes more or 

 less globular or spheroidal in its shape, as the attraction 

 of the substances upon which it is received increases or 

 diminishes ? 



11O0 What is the form of a drop of rain when descending in the air? 



A sphere. 



11O Why should drops of water, resting upon surfaces which have no 

 affinity for them, assume a spheroidal shape? 



Because such surfaces not having so great an attrac- 

 tion for the drops of water as the particles of water have 

 for each other, the drops tend to preserve, as nearly as 

 possible, the spheroidal form which they would have 

 if entirely unsupported, as when falling as drops of 

 rain. 



1111 Is dew ever formed upon the surface of water ? 



The formation of dew upon ships which traverse the 

 vast solitudes of the ocean has never been noticed ; and 

 it has been ascertained by experiment that even a small 

 quantity of water gains no weight by exposure during 

 a single night. 



