SCIENCE-GOSSIP. 



153 



its course. Such side winds would, in particular, 

 be brought into action first on one side and then on 

 the other, whenever the bird passed through the 

 centre of an atmospheric vortex. The exact part 

 played by variations of wind- velocity m the direction 

 of the bird's course is more difficult to understand, 

 but it seems improbable that such variations alone 

 could account for the phenomena. If the bird were 

 moving slowly enough to receive the wind some- 

 times in front and sometimes from behind, it 

 would at intermediate instants be at rest relative to 

 the wind, and would then obtain the minimum 

 degree of support. If it were moving rapidly 

 through the air the latter would always strike the 

 bird in front so that its horizontal motion would 

 be constantly retarded. 



Anyone watching a flock of birds will observe 

 that they often actually are carried up by a sudden 

 side-gust of wind in the manner here described, 

 showing that if this is not the only cause of the 

 phenomena presented by the sailing bird, it is at 

 any rate one of the causes. So much has been 

 written on the subject that it is impossible to say 

 how far these remarks may have been anticipated 

 by other writers, but I think they may help to 

 clear up some of the difficulties which have been 

 experienced in accounting for the sailing of birds. 



The above paper was written at Cambridge, 

 where very few birds are observed to "sail" for 

 any considerable length of time. The explana- 

 tions which were suggested purely by theoretical 

 considerations obtained a striking confirmation in 

 the course of the excursion of the British Association 

 to the Atlantic steamer "Campania," when the 

 author was enabled to watch the gulls sailing on 

 the River Mersey. A strong wind was blowing at 

 the time, so that when the gulls were at rest, the 

 effect was precisely the same as it the birds were 

 moving through still air with a velocity equal and 

 opposite to that of the wind. It was observed 

 that every now and then the wind would swerve 

 round in direction so as to strike the gulls sideways. 

 When this happened the birds would heel over on 

 one side so as to catch the side-wind on the under- 

 side of their wings, and immediately rise in the air. 



Some writers have suggested that the actual 

 velocity of the wind and not the variations of this 

 velocity constitutes the source from which the bird 

 derives its energy. But a knowledge of the laws of 

 mechanics shows that a uniform current of air does 

 not possess any more energy available for a bird 

 floating freely in it than does a mass of air at rest. 

 In the discussion following the reading of the paper, 

 Professor G. F. Fitzgerald, who has himself made 

 some experiments with artificial wings, pointed out 

 that such fallacious arguments were readily met by 

 the consideration that the zuhole of the earth's 

 atmosphere, in consequence of the earth's orbital 

 motion round the sun, is moving at the enormous 



rate of eiglileen miles a second. If we are not able 

 to easily support ourselyes in the air in a wind 

 blowing with this enormous velocity, we thus 

 surely have sufficient proof that a uniform wind is 

 not capable in itself of supporting a bird. 



It is different in the case of a kite fastened to the 

 ground with a string. Here the difference of velocity 

 of the wind and ground— in other words the relative 

 motion of the wind as compared with the point of 

 support — furnishes a source of available energy, and 

 the effect is the same whether the air is in motion 

 and the point of attachment is fixed, or the air is at 

 rest and the kite is being drawn along by a string. 

 Cambridge ; Ociobcv, iSgC. 



RHYNCHOLOPHUS PLUMIPES, 



By C. F. George. 

 'npHIS beautiful and very wonderful looking 

 mite has not (so far as I can ascertain) been 

 recorded as found in the British Isles. When I 

 first saw it I thought it was new to science, but my 

 friend, Mr. Michael, informs me that it was 

 originally found by Lucas, in Algeria (Annal Soc. 

 Entom. France, 4 ser. t. iv., p. 206.), and has also 

 been figured by Haller (" Zur Kentniss der 

 Schweizerischen Milbenfauna," Zeitsch. Wiss., 

 1880) ; it has also been found in Switzerland, and 

 abundantly in Corfu. 



The specimen was found early in August, 1S94, 

 by Mr. W. A. Luff, of Guernsey, on the sand-hills in 

 St. Owen's Bay, Jersey. When he found it, it was 

 moving pretty quickly and carrying its posterior 

 brush-like legs elevated in the air. It is, when 

 alive, of a beautiful scarlet colour, and scattered 

 over its body are a number of club-like hairs. 



The Rhyncholophidse form Koch's second 

 family of earth-mites, and are mostly very hand- 

 some creatures when alive, rejoicing in various 

 beautiful shades of crimson, yellow and black, 

 well deserving their name of ornament-mites. 

 They are somewhat difficult to mount in balsam, 

 and, of course, fluid removes aU their splendid 

 colours ; their legs, also, are difficult to arrange, 

 they are very delicate, and have a tendency to curl 

 up. The best way to kill them for mounting is, I 

 think, to pour boiling water suddenly over them 

 whilst they are moving. They resemble closely 

 Koch's first family of earth-mites, the Trombidida: 

 or velvet mites, so well known by the rather 

 common but very beautiful Trombidium holoscriceum, 

 found often in our gardens. The position of the 

 eyes, as well as their structure, easily distinguish 

 the two families from each other. Koch figures 

 and describes eighteen species, but Rhynclioloplius 

 plumipcs is not one of them, as it was unknown to that 

 author. It would be interesting to know of what use 

 to the creature can be the curious brush-like tarsi. 

 Kirton-in-Lindscy. 



