40 THE ARCHITECTURE OP BIRDS. 



stone. But, then, that this work may not, while it 

 is soft and green, pull itself down by its own weight, 

 the provident 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 suf- 

 ficient time to dry and harden. About half an inch 

 seems to be a sufficient layer for a day. Thus care- 

 ful workmen, when they build mud walls (inform- 

 ed at first, perhaps, 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 a 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. 



" The shell or crust of the nest is a sort of rustic- 

 work full of knobs and protuberances on the outside : 

 nor is the inside of those that I have examined 

 smoothed with any exactness at all ; but is rendered 

 soft and warm, and fit for incubation, by a lining of 

 small straws, grasses, and feathers ; and sometimes 

 by a bedding of moss interwoven with wool. They 

 are often capricious in fixing on a nesting-place, be- 

 ginning many edifices and leaving them unfinished ; 

 but when once a nest is completed in a sheltered 

 place, after so much labour is bestowed in erecting 

 a mansion, as nature seldom works in vain, the same 

 nest serves for several seasons. Those which breed 

 in a ready-finished house, get the start in hatching 

 of those that build new by ten days or a fortnight. 

 These industrious artificers are at their labours in 

 the long days before four in the morning ; when they 

 fix their materials, they plaster them on with their 

 chins, moving their heads with a quick vibratory 

 motion. 



" It has been observed that martins usually build 

 to a northeast or northwest aspect, that the heat 



