40 THE ARCHITECTURE OF 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 abedding 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 
