February, 1907.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



41 



thousand tons, subsided, pushing its foot across the beach 

 until below low-water line. As the sea washed away the base, 

 the mass continued to sink, and fresh horizons were denuded. 

 In 1905 a series of heavy " ground-seas" cast up blocks of 

 limestone and ironstone, containing crocodile bones, which 

 were discovered on the sand between high and low-water 

 marks. The skull came ashore in six pieces, whilst fragments 

 of bones and scutes were constantly picked up, and Mr. 

 Hooley spent many days collecting the remains as the sea 

 sorted them out and cast them up on shore. The specimens 

 were derived from a horizon So to 90 feet below the top of the 

 Wealden Shales. 



The paper describing the discovery was read before the 

 Geological Society of London, and Dr. A. Smith-Woodward 

 in commenting favourably on it remarked that although 

 the remains of Goniopliolis cicissideits were among the com- 

 monest Wealden fossils, the precise characters of the species 

 had remained unknown, until the discovery which the author 

 had described. The new observations were of all the greater 

 value because the Goniopholid:E represented an entirely new 

 departure in the evolution of the Crocodilia at the end of the 

 Jurassic Period, and biologists needed an exact knowledge of 

 the skeleton of these reptiles before they could discuss the 

 meaning of the development in question. The late Sir Richard 

 Owen thought that the first appearance of alligator-shaped 

 crocodiles such as Goniopholis was correlated with the in- 

 coming of warm-blooded quadrupeds and birds. 



ORNITHOLOGICAL. 



By W. P. PvcRAFT, A.L.S., F.Z.S., M.B.O.U., &c. 



The " Dpumming " of the Snipe. 



At the last meeting of the Zoological Society, Mr. Philip H. 

 Bahr gave a most interesting demonstration, illustrating the 

 results of his inquiry into the vexed question as to the mechan- 

 ism which causes the remarkable sounds made by the Common 

 Snipe during the breeding season — sounds which are described 

 by some as "drumming," by others as " bleating." 



While the older naturalists believed these sounds to be 

 vocal, later observers held that they were produced by the 

 wings, and others by the tail. The latter view has been widely 

 accepted for many years, and the experiments which Mr. Bahr 

 made to test the truth of this should remove the last doubts 

 on the subject which some yet maintain. 



He showed conclusively that the principal agents in this 

 matter are the outer tail feathers, which are peculiar, not only 

 in having an unusually thickened and peculiarly curved shaft, 

 but also in the great width of the inner vane. This is further- 

 more strengthened by means of very large and numerous 

 " booklets " — microscopic structures which hold the backs of 

 the feather in position by reason of the grip they take of certain 

 specially modified barbules. 



He extended his examination so as to include every known 

 species of Snipe, and found that in many species the sounds 

 produced are extremely high-pitched, by reason of the narrow- 

 ness of the feathers concerned. This decrease in the width of 

 the vane reaches its maximum in the Pin-Tailed Snipe 

 {Galliiiogo stcnuni), which has furllier increased the number 

 of the tail feathers to 26 pairs ! But here the development 

 has been carried to such an extreme that all sound-producing 

 power has become lost. 



House Martin in December. 



Mr. C. H. Howard, in the Field, December 22, records the 

 fact that he saw a House Martin hawking for flies on the 

 Parade at ICaslbourne on December 9. 



Baiiion's Crake in Kent. 



According to the I'icU, December 22, a Baillon's Crake 

 (Pur::ana hailloni) was shot at Lydd, Kent, on November 24, 

 by Captain R, .-Vlexander, It proved to be a female, and was 

 flushed from a rush-covered pool near the sea. 

 Sea Eagle in Surrey. 



An immature male Sea l^agle (llaliintus (ilhlciUa) was shot 

 at Chevcrills, Surrey, by a gamekeeper on November 12, and 

 was duly recorded, as usual, in the daily Press as a Golden 

 Eagle. This makes the fourth authenticated record of this 

 species for Surrey. 



Honey Buzzard in Wales. 



Mr. H. E. Forrest, in the Zoologist for January, gives a short 

 account of a Honey Buzzard {Pcniis nt>ivorotis} which was 

 •' inadvertently " shot by a keeper at Kerry, near Montgomery, 

 on June 21, igo6. On dissection it proved to be a female. 

 This appears to be the first authenticated record of the 

 occurrence of this species in the county ; while in the whole 

 of North Wales it does not appear to have occurred more 

 than eight times. 



Mediterranean Black-Headed Gull. 



Mr. Forrest, in the same issue of the Zoulogist, brings to 

 light two hitherto unrecorded instances of the occurrence of 

 the Mediterranean Black-Headed Gull {Lams melatiocephahis) 

 in this, countr)'. These birds are now in the collection of 

 Mr. Beville Staines, of Peplow Hall, Salop. They are described 

 in the M.S. Catalogue of Harry Shaw as follows : "The pair 

 of birds in this collection were killed near Falmouth in 

 March, 1S51 ; the only specimens of their kind recorded as 

 obtained in the country." It is certainly remarkable that such 

 rarities should so long have remained in obscurity. 



PHYSICAL. 



By Alfred W. Porter, B.Sc. 



Poulsen-Pederson System of Wireless 

 Telegraphy. 



The great desideratum in wirek^s telegraphy is a system 

 of \v;ivfs which is practically continuous. In Hertzian tele- 

 ijraphy each spark in the sending apparatus lasts for only a 

 small fraction of the time, and the corresponding waves are 

 equally intermittent. A few waves pass, each one less in- 

 tense than the one before it, there is then a long pause 

 before a new series is excited, and this, in turn, rapidly de- 

 creases in intensity. The consequence is that the total 

 effect in any moderate time is very small, and the greatest 

 distance for easy signalling is correspondingly short. It is 

 now claimed by Poulsen that this desideratum is supplied by 

 making use of the singing electric arc. 



Duddell some years ago showed that if a shunt consisting 

 of a suitable inductance and cnp.acity be applied to the 

 terminals of a solid carbon continuous current arc lamp the 

 arc will, under definite conditions, begin and continue to 

 sing. The singing is the audible sign of an oscillatory 

 current in the shunt circuit. By adjusting the inductance 

 and capacity, Duddell was able to obtain very high fre- 

 quencies of alternation amounting to 40,000 periods per 

 second. But with a single arc he was un.ible to satisfy the 

 necessary conditions with a larger current than five amperes. 

 This frequency and current are small compared with what 

 is required for distant wireless telegraphy. Poulsen now 

 claims that by putting the arc in hydrogen or a hydrogen- 

 containing atmosphere a much higher frequency is obtain- 

 .ible ; for example, as high as one million per second; and, 

 moreover, that succeeding oscill.itions are all of equal in- 

 tensity. Improv(Mnent is also elTected by applying a trans- 

 verse magnetic lield to the arc, and also by keeping the 

 anode cool. The l.itter is effected by repl.icing the anode 

 carbon by copper and cooling it with a stream of water. 

 The externals at the sending station do not present much 

 peculiarity. There is the usual antenna attacheil to the 

 oscill.iting circuit. In a large station erected in Denmark 

 the potential difl'erence between antenna and earth amounted 

 to .ibout 2,000 volts, ant! the rate of radiation of energy from 

 the antenna was .about 100 watts, or about one-seventh of 

 that sujjplied to the arc. With this good signals were re- 

 ceived 300 kilometres .iw.iy. Later still greater radi.ilion 

 has been obtained, sulVicient to carry some thousands of 

 metres. .\t the receiving end a special receiver is useil 

 which was devised by Pederson. 



The radiation is received by an antenna whoso circuit is 

 accur.Uelv tuned to the frequency of the w.ives received, so 

 that the principle of resonance is utilised to the fullest ex- 

 tent. To prevent the damping of tliise oscillations the 

 indicating appar.itus is only intermittently connected with 

 the receiver. This intermittent connection is made bv a 

 small, electromagnelically driven interrupter called a 

 Tikker. The indicator itself may be an electrolyte cell, a 



