158 NATURAL HISTORY 
but partly fupports itfelf by ftrongly inclining it's tail againft the 
wall, making that a fulcrum ; and thus fteadied it works and 
plaflers the materials into the face of the brick or ftone. But then, 
that this work may not, while it is foft and green, pull itfelf down 
by it's own weight, the provident archited has prudence and for- 
bearance enough not to advance her work too faft ; but by building 
only in the morning, and by dedicating the reft of the day to food 
and amufement, gives it fufficient time to dry and harden. About 
half an inch feems to be a fufficient layer for a day. Thus careful 
workmen when they build mud-walls (informed at firft perhaps by 
this little bird) raife but a moderate layer at a time, and then defift; 
left the work fliould become top-heavy, and fo be ruined by it's 
own weight. By this method in about ten or twelve days is formed 
an hemifpheric neft with a fmall aperture towards the top, ftrong, 
compad, and warm ; and perfeilly fitted for all the purpofes for 
which it was intended. But then nothing is more common than 
for the houfe-fparrow, as foon as the fhell is finiflied, to feize on it 
as It's own, to ejedt the owner, and to line it after it's own 
manner. 
After fo much labour Is beftowed in ereding a manfion, as 
Nature feldom works in vain, martins will breed on for feveral 
years together in the fame neft, where it happens to be well ftielter- 
ed and fecure from, the injuries of weather. The fhell or cruft of 
the neft is a fort of ruftic-work full of knobs and protuberances 
on the outfide : nor is the infide of thofe that I have examined 
fmoothed with any exadtnefs at all ; but is rendered foft and warm, 
and fit for Incubation, by a lining of fmall ftraws, graffes, and fea- 
thers ; and fometimes by a bed of mofs interwoven with wool. In 
this neft they tread, or engender, frequently during the time of 
building ; and the hen lays from three to five white eggs. 
At 
