mass of matter that at first he could not account for. 

 After some examination, he found that it was the 

 congeries of the bones of mice, and perhaps of birds 

 and bats, that had been heaping together for ages, 

 being cast up in pellets out of the crops of many 

 generations of inhabitants. For owls cast up the 

 bones, fur, and feathers of what they devour, after 

 the manner of hawks. He believes, he told me, that 

 there were bushels of this kind of substance. 



When brown owls hoot their throats swell as his: 

 as a hen's egg. I have known an owl of this species 

 live a full vear without anv water. Perhaps the case 

 may be the same with all birds of prey. When owls 

 fly they stretch out their legs behind them as a bal- 

 ance to their large heavv heads: for, as most noc- 

 turnal birds have large eyes and ears thev must have 

 large heads to contain them. Large eves I presume 

 are necessary to collect every ray of light, and large 

 concave ears to command the smallest degree of 

 sound or noise. ^ 



The liirundincs are a most inoffensive, harmless, 

 entertaining, social, and useful tribe of birds ; they 

 touch no fruit in our gardens; delight, all except 

 one species, in attaching themselves to our houses; 

 amuse us with their migrations, songs, and marvellous 



* It will be proper to premise here that the Letters LIIL. LV., LVIL. 

 and LX., have been published already in the " Philosophical Trans- 

 actions," but nicer observation has furnished several corrections and 

 additions. 



187 



