184 
NATURAL HISTORY 
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. 
They dip and wash as they fly sometimes in very hot 
weather, but not so frequently as swallows. It has been 
observed that martins usually build to a north-east or north- 
west aspect, that the heat of the sun may not crack and 
destroy their nests : but instances are also remembered 
where they bred for many years in vast abundance in a hot 
stifled inn-yard, against a wall facing to the south. 
Birds in general are wise in their choice of situation : but 
in this neighbourhood, every summer, is seen a strong 
instance to the contrary at a house without eaves in an 
exposed district, where some martins build year by year in 
the corners of the windows. But, as the corners of these 
windows (which face to the south-east and south-west) are 
too shallow, the nests are washed down every hard rain; 
and yet these birds drudge on to no purpose from summer 
to summer, without changing their aspect or house. It is 
a piteous sight to see them labouring when half their nest 
is washed away, and bringing dirt — generis lapsi sarcire 
ruinas.^' Thus is instinct a most wonderfully unequal 
faculty : in some instances so much above reason, in other 
respects so far below it ! Martins love to frequent towns, 
especially if there are great lakes and rivers at hand ; nay, 
they even affect the close air of London. And I have not 
only seen them nesting in the Borough, but even in the 
Strand and Fleet Street ; but then it was obvious from the 
dinginess of their aspect that their feathers partook of the 
filth of that sooty atmosphere. Martins are by far the least 
agile of the four species ; their wings and tails are short, 
and therefore they are not capable of such surprising turns 
and quick and glancing evolutions as the swallow. Accord- 
ingly they make use of a placid easy motion in a middle 
region of the air, seldom mounting to any great height, and 
never sweeping long together over the surface of the ground 
or water. They do not wander far for food, but affect 
