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hawks, shrikes, polecals, and indeed on all animals of prey, must have met the observation of almost every person, all the weakest and most helpless birds in a neighbourhood uniting in a body to drive the invaders away. I have somewhere met with an account of a similar attack made upon a hunting spider by flies, though we must look upon this as quite anomalous, for amongst thousands of these spiders, whose proceedings I have watched, I never observed such an occurrence. But connected with such singular attacks of the weak upon the strong, a much more remarkable circumstance is frequently witnessed; for, passing over the cuckoo, who is persecuted by small birds, evidently because they mistake him for a hawk,* most night birds are attacked in the same way, whenever they make their appearance by day. We might, perhaps, refer this in the case of owls to the general principle, though owls seldom, I believe, prey upon birds, if they can procure mice and other small quadrupeds; but what are we to think of the night-jar (Nyctichelidon Europæus, RENNIE), which is subjected to similar persecution ? This poor bird appears, indeed, to be the butt of innumerable mistakes in all quarters ; for, though it feeds, like the bat, upon nocturnal moths and other night-flying insects,—the small birds show, by the attacks they make upon it, that they believe it to prey upon them. The name also, which it has received in all languages of youtsucker (most absurdly continued by most recent naturalists in the term Caprimulgus), shows the opinion entertained of it by the vulgar. It is, however, as impossible for the night-jar to suck the teats of cattle,
* Sce Insect Transformations, page 78.
(though most birds are fond of milk *), as it is for cats to suck the breath from sleeping infants, of which theyare absurdly accused, inasmuch as the structure of their organs would baffle any such attempt.
RADIATED CLOUDS.— Even when the sky is serene, it is not uncommon to see one or more clouds, usually white, light, in form of streaks, in arch-formed curves, and directed to some opposite point of the horizon. This sort of cloud is called a rayed or streak-cloud. The opposition may take place in two ways, either in the entire circle of the horizon, or in the half-circle. If the ray pass through the zenith, its extremities will necessarily stretch to points which are diametrically opposite in the entire circle. When there are several rays, they commonly converge in two opposite points in the entire circle of the horizon, and this group or system of rays is what I call a meteorological radiation. The point in which the rays become united together, whether real or supposed, may be called the converging point. It is real, if the rays are continuous; and supposed, if they are broken or interrupted. It is but seldom, however, that
* See Sweet's British Warblers, passim.
rays meet in one point. It more frequently happens, that they issue from a small mass which is of various shades of color, but generally grey or whitish ; and this I have named the focus of radiation. In this mass the rays melt away, or are lost. The conver. gence of rays to a single focus is sufficient to constitute a radiation : but as it is the nature of rays to stretch towards two opposite foci, it is probable, that the convergence towards the second focus is prevented by circumstances, which do pot render the phenomenon at all extraordinary. The radiation, consequently, will be only partial in one case, and entire in the other. If the rays be more apparent on one side than on the other, the radiation is unequal—and if the rays appear on one side only, it is then incomplete, or unilateral It is irregular when the rays are sinuous, or ill-disposed ; — direct when the middle ray passes towards the ze. nith, while the lateral rays on each side have the same inclination in respect of the horizon. Itis inclined or oblique, when the rays on one side are nearer to the horizon than the cor
responding rays on the other side. I may remark, that sometimes, according to the degree of the obliquity, the two points of convergence are not directly opposite. Rays may be spread. at unequal distances
—and the separation, great or little, of the extreme rays may be denominated the amplitude of the radiation. The axis is a line which may be supposed to be drawn from one point of convergence to the other.
There are radiations, the rays of which are equal, or nearly alike. There are others, the rays of which are unequal, either in their dimensions, or in their consistency and color. For instance ; on one side, they may be united, fine, light, or wbite; on the other side, thick, black, large, dappled : and sometimes, even the lower are in well defined streaks.
We have bitherto spoken of radiation, as if the two points of convergence were exactly in the horizon. But it is not always thus ; for both are often above the horizon, and sometimes they are below, though it more frequently occurs, that radiation is disposed in such a manner that one of them is above, and the other below.
I have often observed, that when the axis of the radiation is drawn from one equinoctial point to another, the two points of convergence are in the horizon, or equally elevated above the horizon ; and that when the axis is in the direction of north to south, or reciprocally, the focus or point of convergence on the north, is raised above the horizon, whilst that on the south is below. The disposition is rarely otherwise, and seems to favour the opinion of the ancients, that the winds blew downwards from the north, and upwards from the south. It is, however, unknown to me, whether that opinion was founded upon an exact observation of facts, or whether it was only a hypothetical consideration originating from the elevation of the pole in our northern climates. It is, at all events, certain, that, in general, the point of radiation is so much raised above the horizon as to correspond directly with due north ; and if it be not placed in such a situation (which frequently happens) it is progressively lower in proportion as the focus approaches the east or the west.
Radiation is moreover a phenomenon so common, that few days pass without our having an opportunity of observing it. Radiations may be seen to succeed each other without interruption for some time. Nevertheless, there is no mention made of them in treatises of Meteorology. Mons. de Lamarck alone has, I think, in his Calender designated them by the name of Barred Clouds. But this iilustrious author has paid but little attention to the characteristics of the phenomena. As for me, I attach so much importance to it, that I regard it as the key to almost all the appearances of the celestial vault. *
That this phenomenon did not attract earlier atten
* See a paper on this subject, with figures, by J. Rennie, Mag. Nat. Hist. vol. i.