February, 1906.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



361 



been put up, but according to the authors nests have been 

 supplied to save the birds the trouble of building. " The 

 Department," he .says, " has undertaken the supply of arti- 

 ficial nests suitable' for the different species ... for 

 swallows, moss or a few dead leaves are provided" ! Either 

 the translator has misread some portion of the original 

 account of this work, or the well-meaning authors of these 

 nests have not so wide a knowledge of field ornithology as 

 we should expect. Be this as it may, the provision of nest- 

 boxes, and the efTorts to encourage these birds, is a step in 

 the right direction. In this country the question of the pro- 

 tection of birds is a cause of much difference of opinion ; 

 and we shall never arrive at any satisfactory solution of the 

 problem until the matter is taken up by the Beard of Agri- 

 culture as is done in Germany and .America. 



Lesser Grey Shrike at Chichester. 



At the last meeting of the British Ornithologists' Club (Dec, 

 1905), Mr. A. F. Griffith exhibited a specimen, in autumn 

 plumage, of the Lesser Grey Shrike {Laniiis minor), which had 

 been killed near Chichester in (October, 11)05. 



Little Shearwa-ter a.t Lydd. 



At the meeting above referred to a male example of the 

 little dusky Shearwater {Puffinus assiintlis), which had been 

 captured at Lydd. in Kent, was exhibited on behalf of Dr. 

 N. F. Ticehurst. This bird, which marks the fourth occur- 

 rence of this species in Britain, was taken alive after the 

 south-west gale of Nov. 26. 



Breeding Place of Ross's Gvill. 



Mr. H.E. Dresser at this same meeting announced the fact 

 that a breeding place of Ross's Gull (Rhudustcthia i-ossi) had 

 been recently found in the Kolyma delta, North-East Siberia. 

 Mr. Bnterlin, a Russian naturalist, the fortunate discoverer, 

 procured an adult bird, young in down, and eggs. 



PHYSICAL. 



Bv Altred W. Porter, B.Sc. 



Instrument for Compounding Vibrations. 



The following means of compounding several harmonic 

 motions, all taking place parallel to one straight line, is de- 

 scribed by Lord Rayleigh in the Philosopliical Magazine for 

 January. 



" A wooden batten, say i inch square and 5 feet long, is so 

 mounted horizontally as to be capable of movement only along 

 its length. For this purpose it suffices to connect two points 

 near the two ends, each by means of tn'O thin metallic wires 

 with four points symmetrically situated in the roof overhead. 

 . . . The movement of the batten along its length is controlled 

 by a piece of spring-steel against which the pointed extremity 

 of the batten is held by rubber bands. Any force acting in the 

 direction of the length of the batten produces a displacement 

 proportional to the force. The tracing point by which the move- 

 ments are recorded is at the other cud, as nearly as possible in 

 the line joining the two ponits of attachment of the four suspend- 

 ing wires. The longitudinal forces are due to the vibrations 

 of pi'ndulums hanging from horizontal cross pieces attached 

 to the batten at their centres. The two ends of a wire or 

 cord are attached to the extremities of a cross piece, the bob 

 of the pendulum being a mass of lead (perhaps half a pound) 

 at the middle of the cord. When set swinging the movements 

 of the pendulums are thus parallel to the batten, and tend to 

 displace it along its length." The smoked paper or glass upon 

 which the style leaves a trace must, of course, be given in 

 addition a uniform motion either by drawing it along a guide, 

 or by rotating it in its own plane like the face plate of a lathe. 

 If done in the latter way excellent lantern slides may after- 

 wards be made by photography showing the resultant etTect 

 of combining simple harmonic motions in the way described. 

 If it be required to make the component vibrations have 

 periods in simple proportion to one another, it must be re- 

 membered that the period of a pendulum is proportional to the 

 square root of its length (i.e., in this case the distance of the 

 centre of the bob to the centre of the hue joining the ends 

 of its suspending wires). For example, the elTectof combin 

 ing a note and its octave (which has half the period of the note) 

 can be illustrated by having two pendulums only, whose 

 lengths are, say, 4 feet and i foot. 



Active Deposit from Radium. 



Dr. H. L. Broasoa shows (i) that temperatures between 

 700° and II 3o' C. do not psrmaneatly afifect the rate of decay 

 of the active deposit from radium; (2) That radium B and 

 not radium C has the longer decay period ; (3) Thit the pre- 

 vious values of twenty-eight and twenty-one minutes are both 

 too large for the decay periods of radium B and C respectively; 

 and that twenty-six and nineteen minutes are much closer to 

 the true values. 



ZOOLOGICAL. 



By R. Lydekker. 

 Regenerai-tion in Mammals. 



At the December meeting of the Zoological Society was ex- 

 hibited the skeleton of the tail of a dormouse showing distinct 

 evidence of reparation after an accident ; this being apparently 

 the first recorded instance of the regeneration of bony struc- 

 ture in mammals. 1 he re-formed vertebra, which had assumed 

 the form of a slender rod, was composed externally of true 

 bone, whereas in the regenerated tails of lizards the new 

 structure consists of calcified fibro-cartilage. 



Spicules of Sponges. 



A remarkable instance of diversity of view is exemplified by 

 two explanations which have recently been offered of the 

 function of the triradiate mineral spicules found in many sponges. 

 A writer in the Xo\ember issue of the American Saturalist 

 tells that these structures at first merely took the form of small 

 spiny developments in the flesh in order to prevent sponges 

 from being eaten by other creatures. .As time went on these 

 spicules were carried to the perfection of symmetrical devel- 

 opment by what the author is pleased to call " momentum," 

 that is to say, the continuance of development along a particu- 

 lar line long after any useful result accrues to the animal in 

 which such evolution takes place. By a curious coincidence, 

 in the Quarterly Journal of Microscopical Science for the very 

 same month, an English naturalist points out that these tri- 

 radiate spicules are probably a special adaptation to prevent 

 the stems of slender sponges from being broken by the action 

 of the waves of the shallow water in which they grow ; the tri- 

 radiate form affording protection in three different planes. 

 The moral of this is, Never affirm a structure to be useless 

 unless you are absolutely sure there is no possible purpose 

 it can serve. 



Fossil Flying-fishes. 



Fossil flying-fishes form the subject of an interesting and 

 well-illustrated communication by Dr. O. .Abel to the Vear- 

 Book of the Austrian Geological Survey. .\t the present day 

 there are two distinct types of flying-fishes, namely, the flying- 

 gurnards and the flying-herrings, the latter being what may be 

 called the typical flying-fishes ; and it is quite evident that each 

 of these has acquired its powers of flight quite independently 

 of the other. Similarly, Dr. .Abel shows that in past geological 

 times several kinds of fishes, totally distinct from the modern 

 types, possessed long pectoral fins, which were intended, in 

 all probability, to enable their owners to skim the surface of 

 the water in flying-fish fashion. The earlier of these fishes — 

 Thoracopteriis and Gii;antoplenis — occur in strata belonging to 

 the period of the Trias, or New Red Sandstone, and, like their 

 non-flying contemporaries, had their bodies encased in an 

 irmour of quadrangular enamel-covered scales. 



Papers Rea-d. 



At the meeting of the Zoological Society held on Decem- 

 ber 12, Mr. 11. R. Hogg read a paper on South African 

 spiders of the family l.ycosiiiir : Mr. O. Thomas discussed 

 mammals collected in Persia, describing a new genus and 

 ipecies of hamster-like rodent allied to the North .-Vnierica Pero- 

 inyscus; colour-variation in a beetle formed the subject of a 

 connnunication by Mr. L. Doncastor : the Society's Prosecter 

 discoursed on new worms ; Dr. de Man described a crab and a 

 orawn from Christmas Island ; the heredity of webbed feet in 

 pigeons was discussed by Mr. Iv. S. Browne ; while Messrs. 

 W'arbuvton and Pearce gave an account of new and rare 

 British Oribatida:. 



