272 NATURAL HISTORY 



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 rimias." Thus is instinct a 

 most wonderful 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. Mar- 

 tins 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. Accordingly 

 they make use of a placid easy motion iu 



