128 WHITE 



some examination he found that it was a 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 big as a hen's 

 egg. I have known an owl of this species live a full year 

 without any 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 balance to their large heavy heads, for as 

 most nocturnal birds have large eyes and ears they must have 

 large heads to contain them. Large eyes I presume are neces- 

 sary to collect every ray of light, and large concave ears to com- 

 mand the smallest degree of sound or noise. I am, etc. 



[It will be proper to premise here that the sixteenth, eigh- 

 teenth, twentieth, and twenty-first letters have been published 

 already in the " Philosophical Transactions ; " but as nicer 

 observation has furnished several corrections and additions, it 

 is hoped that the republication of them will not give offence ; 

 especially as these sheets would be very imperfect without 

 them, and as they will be new to many readers who had 

 no opportunity of seeing them when they made their first 

 appearance.] 



" The hirundines are a most inoffensive, harmless, entertain- 

 ing, social, and useful tribe of birds ; they touch no fruit in our 

 gardens; delight, all except one species, in attaching them- 

 selves to our houses ; amuse us with their migrations, songs, 

 and marvellous agility ; and clear our outlets from the annoy- 

 ances of gnats and other troublesome insects. Some districts 

 in the south seas, near Guayaquil, are desolated, it seems, by 

 the infinite swarms of venomous mosquitoes which fill the 

 air and render those coasts insupportable. It would be worth 

 inquiring whether any species of hirundines is found in those 

 regions. Whoever contemplates the myriads of insects that 

 sport in the sunbeams of a summer evening in this country, 



