clings with its claws, but partly supports itself by 

 strongly inclining its tail against the wall, making 

 that a fulcrum ; and thus steadied, it works and plas- 

 ters the materials into the face ot the brick or stone. 

 But then, that this work may not, while it is soft and 

 green, pull itself down by its own weight, the provi- 

 dent architect has prudence and forbearance enough 

 not to advance her work too fast ; but by building 

 only in the morning, and by dedicating the rest of 

 the day to food and amusement, gives it sufficient 

 time to dry and harden. About half an inch seems 

 to be a sufficient layer for a day. Thus careful work- 

 men when they build mud-walls (informed at first per- 

 haps by this little bird) raise but a moderate layer at 

 a time, and then desist ; lest the work should become 

 top-heavy, and so be ruined by its own weight. By 

 this method in about ten or twelve days is formed an 

 hemispheric nest with a small aperture towards the 

 top, strong, compact, and warm ; and perfectly fitted 

 for all the purposes for which it was intended. But 

 then nothing is more common than for the house- 

 sparrow, as soon as the shell is finished, to seize on it 

 as its own, to eject the owner, and to line it after its 

 own manner. 



After so much labour is bestowed in erecting a 

 mansion, as Nature seldom works in vain, martins 

 will breed on for several years together in the same 

 nest, where it happens to be well sheltered and se- 

 cured from the injuries of weather. The shell or 



ig6 



