October 1, 1895.] 



KNOWLEDGE 



219 



and turning round sat back to the birds, holding the 

 camera in one hand in front of me and pointing it over 

 my shoulder. Thus the right distance and elevation 

 •were obtained, and the result may be seen in the two 

 accompanying illustrations. It will be noticed that the 

 birds are very much huddled up and sleepy -looking in 

 both photographs, but having my back to them it was 

 impossible to keep them in good attitudes. In the small 

 illustration the bough from which the growth sprang may 

 be traced back to the trunk, and the general position of 

 the growth itself is better seen than in the large one. 



A great deal of time and a certain amount of patience 

 are undoubtedly needed in photographing birds and beasts 

 from life. There are svu-e to be many disappointments, 

 even after an immense amount of trouble has been taken. 

 Nevertheless, let me urge upon field-naturalists the im- 

 portance of taking up photography as not only a pleasure, 

 but an extremely useful adjunct in their pursuit. 



To pass on from photoi^'raph to subject, it may be said 

 that the kestrel hawk,* which is a tolerably common bird 

 in the British Isles, will no doubt increase in numbers 

 now that farmers and gamekeepers are beginning to under- 

 stand its usefulness. Just as there are " rogue " elephants, 

 so there are " rogue " kestrels. These will go into the 

 pheasant held and take the young chicks. But it has 

 been well said, " Never shoot a kestrel unless you see 

 it in the act of doing damage." 



The usual food of the kestrel is composed of rats, mice, 

 small birds, beetles and other insects, and of the first two 

 it destroys great numbers. Its graceful movements in 

 the air when in search of food demand admiration from 

 everyone. Hovering over a field, suspended as it were in 

 space, it seems fixed and motionless but for the rapid 

 beats of the wings. This feat, which has won for it the 

 name of " windhover," is by no means an ordinary one. 

 Few birds, and no other British hawk, can accomplish it, 

 and the kestrel itself would be unable to hover, did it not 

 make use of the wind, however little there may be stirring. 

 When in the act of hovering, it invariably has its head to 

 the breeze ; and its body is placed at such an angle, 

 according to the strength of the wind, that the bird is 

 stationary in space. The forces of the wind and 

 wings meet and balance each other, while both help 

 in counteracting gravity. It will be noticed that on a 

 very windy day the kestrel's position when hovering is 

 almost parallel to the ground, while on a very still one it 

 is almost vertical. From its elevated position it takes in 

 the surrounding land at a glance, and the smallest mouse 

 in the grass beneath will not escape its keen sight. With 

 a downward swoop it drops on its prey like a stone, and 

 transfixes it with its sharp talons before escape is possible. 

 One of the most striking sights in bird life I have ever seen 

 was the action of three kestrels as they hunted a mouse- 

 infested wheat stack. They hovered above it with the 

 sides well in view, and every time a mouse incautiously 

 appeared at the edge, one of the birds dropped down upon 

 it, and, clinging to the side for a moment. Hew ofi' again to 

 devour the captive in a neighbouring clump of trees, from 

 which it soon returned to renew the hunt. 



The kestrel very rarely builds its own nest. A hole or 

 a ledge in a clift' or quarry is a favourite site in many 

 districts. In woods it uses a hole in a tree or an old or 

 deserted nest of a crow, magpie, or some such bird, in 

 which to lay its eggs. These are five or six in number, 

 thickly speckled with rich brown. The yoimg are at first 

 covered with down, and when in this condition they are 

 harmless. Nevertheless, they place themselves in all sorts 



* Faleo finnujiculus. 



of defensive attitudes. To lie on their backs with open 

 mouths, and tear at the intruder with their claws is a 

 favourite position, while at other times they stand up in 

 the nest, and. Happing their wings, strike with the beak. 



At all times and at every age the kestrel hawk is an 

 extremely interesting bird, and in captivity it forms a 

 most pleasing pet. 



THE INTERNATIONAL GEOGRAPHICAL 

 CONGRESS IN LONDON. 



(Continued from paye 106.) 



OCEANOGEAPHY. 



THIS subject was opened by Mr. J. Y. Buchanan, 

 F.E.S., who, after referring to the London 

 Congress as coinciding with the completion of 

 the Chdllenycr Report, proposed to look back 

 to the state of the oceanography before, during, 

 and since the great expedition, and at the direction which 

 investigations should take later on. On the first lino of 

 soundings across the North Atlantic the Chdhmjer 

 found the calcareous deposits limited by depth, and 

 discovered the abysmal ochreous and argillaceous deposits, 

 and peroxide of manganese was found in all of the earliest 

 dredgings. The limitation by depth of the calcareous 

 deposits suggested to Sir Wyville Thomson his solution 

 theory. The areometric method of ascertaining salinity 

 was approved, and the instruments used in expeditious, 

 from the time of the Cliallcnijer to the present, were 

 particularly described, and the possibilities in the improve- 

 ment of oceanographical instruments were adverted to. 



The Prince of Monaco contributed a paper detailing the 

 recent work of his yacht the Princrsse Alice, which 

 had been built and fitted specially for oceanographical 

 investigation. Soundings are made by a cable of three 

 strands, each of three very fine steel wires, the whole 

 only one-tenth of an inch in diameter, and very flexible. 

 Very important zoological discoveries were made by a 

 deep-sea trap of wood and network, on the principle of the 

 lobster-pot, for many of the animals obtained by it could 

 not have been procured by the ordinary trawl or dredge. 

 It is suspended by thirty fathoms of rope, connected by a 

 swivel with a steel wire cable of four thousand fathoms, 

 in lengths of two hundred and fifty fathoms, easily 

 separated at any joining. This apparatus showed that 

 the deepest waters of the western Mediterranean swarmed 

 with highly organized life, and valuable biological results 

 were obtained in the Bay of Biscay at a depth of two 

 thousand seven hundred fathoms, whUe a fish, Macuius, 

 two feet six inches long, and some remarkable holothurians 

 had been brought from a depth of two thousand fathoms. 

 A submerged electric light for attracting specimens had 

 also been used with success. 



A paper by Captain A. S. Thomson, R.N.E., classified 

 the movements of ocean water as stream currents, flowing 

 at the surface and occasionally extending to a considerable 

 depth ; counter currents, which return the excess of water 

 conveyed away by the induction of the stream currents ; 

 drift currents, due to winds blowing continuously more or 

 less in the same direction ; and perimlic and sidi-surface 

 currents. Sub-surface currents form an important factor 

 in oceanic circulation, and offer a rich field for scientific 

 discovery. Evaporation is the chief cause of oceanic 

 circulation. In the trade-wind regions, from each square 

 inch of surface in twenty-four hours, a cubic inch of water 

 evaporates, and the current chart of the world shows that 

 the principal surface currents circulate round the areas 



