one drop on the back of another, and both of them sink down together for many fathoms with a loud piercing shriek.  This I take to be the juncture when the business of generation is carrying on.

As the swift eats, drinks, collects materials for its nest, and, as it seems, propagates on the wing, it appears to live more in the air than any other bird, and to perform all functions there save those of sleeping and incubation.

This hirundo differs widely from its congeners in laying invariably but two eggs at a time, which are milk-white, long, and peaked at the small end; whereas the other species lay at each brood from four to six.  It is a most alert bird, rising very early, and retiring to roost very late; and is on the wing in the height of summer at least sixteen hours.  In the longest days it does not withdraw to rest till a quarter before nine in the evening, being the latest of all day-birds.  Just before they retire whole groups of them assemble high

in the air, and squeak, and shoot about with wonderful rapidity.  But this bird is never so much alive as in sultry thundery weather, when it expresses great alacrity, and calls forth all its powers.  In hot mornings several, getting together in little parties, dash round the steeples and churches, squeaking as they go in a very clamorous manner; these, by nice observers, are supposed to be males serenading their sitting hens; and not without reason, since they seldom squeak till they come close to the walls or eaves, and since those within utter at the same time a little inward note of complacency.

When the hen has sat hard all day, she rushes forth just as it is almost dark, and stretches and relieves her weary limbs, and snatches a scanty meal for a few minutes, and then returns to her duty of incubation.  Swifts, when wantonly and cruelly shot while they have young, discover a little lump of insects in their mouths, which they pouch and hold under their tongue.  In general they feed in a much higher district than the other species—a proof that gnats and other insects do also abound to a considerable height in the air; they also range to vast distances, since locomotion is no labour to them who are endowed with such wonderful powers of wing.  Their powers seem to be in proportion to their levers, and their wings are longer in proportion than those of almost any other bird.  When

they mute, or ease themselves in flight, they raise their wings, and make them meet over their backs.

At some certain times in the summer I had remarked that swifts were hawking very low for hours together over pools and streams, and could not help inquiring into the object of their pursuit that induced them to descend so much below their usual range.  After some trouble, I found that they were taking phryganeæ, ephemeræ, and libellulæ (cadew-flies, may-flies, and dragon-flies), that were just emerged out of their aurelia state.  I then no longer wondered that they should be so willing to stoop for a prey that afforded them such plentiful and succulent nourishment.

They bring out their young about the middle or latter end of July: but as these never become perchers, nor, that ever I could discern, are fed on the wing by their dams, the coming forth of the young is not so notorious as in the other species.

On the 30th of last June I untiled the eaves of a house where many pairs build, and found in each nest only two squab, naked pulli; on the 8th July I repeated the same inquiry, and found that they had made very little progress towards a fledged state, but were still naked and helpless.  From whence we may conclude that birds whose way of life keeps them perpetually on the wing would not be able to quit their nest till the end of the month.  Swallows and martins,

that have numerous families, are continually feeding them every two or three minutes, while swifts, that have but two young to maintain, are much at their leisure, and do not attend on their nest for hours together.

Sometimes they pursue and strike at hawks that come in their way, but not with that vehemence and fury that swallows express on the same occasion.  They are out all day long in wet days, feeding about, and disregarding still rain: from whence two things may he gathered; first, that many insects abide high in the air, even in rain; and next, that the feathers of these birds must be well preened to resist so much wet.  Windy, and particularly windy weather with heavy showers, they dislike, and on such days withdraw, and are scarce ever seen.

There is a circumstance respecting the colour of swifts which seems not to be unworthy of our attention.  When they arrive in the spring, they are all over of a glossy, dark soot-colour, except their chins, which are white; but, by being all day long in the sun and air, they become quite weather-beaten and bleached before they depart, and yet they return glossy again in the spring.  Now, if they pursue the sun into lower latitudes, as some suppose, in order to enjoy a perpetual summer, why do they not return bleached?  Do they not rather perhaps retire to rest for a season, and

at that juncture moult and change their feathers, since all other birds are known to moult soon after the season of breeding?

Swifts are very anomalous in many particulars, dissenting from all their congeners not only in the number of their young, but in breeding but once in a summer, whereas all the other British hirundines breed invariably twice.  It is past all doubt that swifts can breed but once, since they withdraw in a short time after the flight of their young, and some time before their congeners bring out their second broods.  We may here remark that, as swifts breed but once in a summer, and only two at a time, and the other hirundines twice, the latter, who lay from four to six eggs, increase at an average five times as fast as the former.

But in nothing are swifts more singular than in their early retreat.  They retire, as to the main body of them, by the 10th August, and sometimes a few days sooner; and every straggler invariably withdraws by the 20th, while their congeners, all of them, stay till the beginning of October—many of them all through that month, and some occasionally to the beginning of November.  This early retreat is mysterious and wonderful, since that time is often the sweetest season in the year.  But what is more extraordinary, they begin to retire still earlier in the most southerly parts of Andalusia, where they can be

in no ways influenced by any defect of heat, or, as one might suppose, failure of food.  Are they regulated in their motions with us by a defect of food, or by a propensity to moulting, or by a disposition to rest after so rapid a life, or by what?  This is one of those incidents in natural history that not only baffles our searches, but almost eludes our guesses!

These hirundines never perch on trees or roofs, and so never congregate with their congeners.  They are fearless while haunting their nesting-places, and are not to be scared with a gun, and are often beaten down with poles and cudgels as they stoop to go under the eaves.  Swifts are much infested with those pests to the genus called hippoboscœ hirundinis; and often wriggle and scratch themselves in their flight to get rid of that clinging annoyance.

Swifts are no songsters, and have only one harsh screaming note; yet there are ears to which it is not displeasing, from an agreeable association of ideas, since that note never occurs but in the most lovely summer weather.

They never can