526 



NA rURE 



[March 31, 1887 



the flowers, Dr. King is of opinion tliat the evolutionary history 

 ■of the genus Ficiis may be traced. On data derived th^refrom 

 he arranges the Indo-Mil.ayan species into two great groip;, 

 the second of these being again divided into three subsidiary 

 sub-groups as follows : — 



i Group I. Pseudo-her.naphrodite. . Palxraiorphe 



j I Sect. I . , Urostigmi 



_. I Sect. 2 . . Synoe;ia 



<:'f"'' ' Group II. Unisexual ) f , f Sycidium 



^•""■| Is^c, , ) icovellia 



!, I ' ' \N;omorphe 



Physical Society, Ma-ch 12. — Prof. G. Carey Foster, Vice- 

 President, in the chair. — Mr. Shelford Bidwell described some 

 e.xperiments which seem to show that the electrical resistance of 

 suspended copper and iron wires, alters with the direction of the 

 testing current. The apparatus used consisted of a metre bridge 

 with coils of too ohms in the gaps adjoining the standard wire, 

 the other two arms being two suspended wires united at the top, 

 to which point one terminal of the galv.anometer was joined. A 

 commutator placed in the battery circuit served to reverse the 

 testing current. When a wire is suspended vertically the stress 

 increases from below upwards, and the author believes the 

 observed effects to be due to the absorption of heat by the current 

 as it passes from a stretched towards an unstretclted part of a 

 copper wire, and the evolution of heat when it passes from an 

 unstretched towards a stretched part. As the apparatus was 

 arranged the current passed up one side and down the other, 

 heating the one and cooling the other, thus disturbing the 

 position of balance. If iron wires were used the heating and 

 cooling effects were reversed. Prof. S. P. Thompson suggested 

 loading the wires at different points in order to vary the stress 

 without using such long wires, and Mr. C. V. Boys thought still 

 shorter wires could be used by joining the ends to a revolving 

 spindle and stretching them by centrifugal force. — On a lecture 

 experiment in self-induction, by Mr. Shelford Bidwell. A tele- 

 phone is placed in series with the secondary coil of an induction 

 coil and another coil whose self-induction can be raised by 

 inserting a core of iron wires, or another coil, or both. The 

 effect of introducing the iron core is very marked, reducing the 

 sound enormously. If a coil of wire containing an iron core be in- 

 serted, the effect of short-circuiting the coil is to increase the sound 

 in the telephone. The same author also described and showed 

 ail experiment due to Dr. Fleming, in which a disk of copper 

 inclined at an angle of 45° to the axis of a coil of wire and sus- 

 pended bifilarly, is deflected by passing an undulatory current 

 round the coil. In expl.anation of the former experiment. Dr. 

 Fleming wrote down the formulae for the effective resistance and 

 self induction of a circuit near another closed circuit, which 

 show that the former is greater and the latter less for uudulatoi-y 

 than for steady currents. He had not arrived at any satisfactory 

 explanation of the deflection of tlie copper disk. Prof Ayrton 

 exhibited a tuning-fork worked electrically, in which the pitch 

 could be varied by altering the self-induction of the circuit, or 

 by vai-ying the position of the make-and-break screw. Mr. C. 

 V. Boys referred to his experiments, published in 1S84, on the 

 impulse given to metal disks suspended in a magnetic field 

 whose strength is suddenly changed, as being of a similar 

 character to that described by Mr. Bidwell, and suggested the 

 use of aluminium instead of copper in future experiments, owing 

 to its conductivity for the same weight being greater. Prof. 

 Thompson said he had recently used a similar apparatus to that 

 described by Mr. Bidvvell as an illustration of the effect of self- 

 induction, and pointed out the uses of self- and mutual-induction 

 in multiplex telegraphy and telephony. As an explanation of 

 the deflection of the copper disk by alternating currents. Prof. 

 Foster thought it possibly due to its initial position being that 

 of maximum sensibility, and therefore each impulse had less 

 effect than the preceding one. Mr. W. M. Mordey mentioned 

 a simple arrangement for varying self-induction used by Mr. 

 Ferranti to control the power of incandescent lamps worked by 

 alternating currents, and Prof. Ayrton described a closed mag- 

 netic circuit of gi'eat self-induction, used to protect voltmeters 

 on the telpher line at Glynde from disastrous inductive effects 

 produced by breaking the locomotive circuit. Referring to 

 tuning-forks, Mr. Bosanquet thought some self-induction was 

 necessary in order that the current should act to the best 

 advantage in attracting the prongs at the proper instant. 

 Further remarks were made by Mr. Boys and Prof Perry. — On 



a lecture experiment to show that capacity varies inversely as 

 the thickness of the dielectric, by Profs. W, E. Ayrton and 

 John Perry. The authors consider it easy for students to see 

 that, other things remaining constant, capacity is proportional to 

 area. Taking this as proved, a condenser is arranged such 

 that the area A of the insulated inner coating varies as the 

 thickness t of the dielectric, and the potential difference between 

 the coatings is found by experiment to be constant. Then since 



capacity = 1"^"''')'.^ ^nd both the latter being constant, there- 

 potential 

 fore the capacity of the condenser is constant. But by the con- 

 struction of the apparatus - is constant, and it is assumed that 



capacity varies as A, therefore capacity must vary inversely as /. 

 — Note on magnetic resistance, by the same authors. Two iron 

 rings about 6 inches diameter, made from the same bar of best 

 Swedish iron about half an inch in diameter, were wound with 

 insulated wire in two halves, so that a current could be sent 

 round either or both halves, and the resulting induction measured 

 by the throw of a ballistic galvanometer placed in series with a 

 few convolutions of wire wound round the outside of the main 

 winding. One of the rings was continuous, and the otlier had a 

 small air space of about o'8 mm. in a plane perpendicular to that 

 of the ring and passing through its axis, as if the ring had been 

 cut by a saw. The primary object of the experiments, which 

 were made by Messrs. Aldworth, Dykes, Lamb, Robertson, 

 and Zingler, of the Central Institution, was to determine 

 whether there was any appreciable "surface magnetic resistance." 

 The resvdts do not show any such resistance, and the relative 

 resistance of air and iron as calculated from the unsaturated 

 parts are about as 1200 to i, a number agreeing fairly well with 

 those obtained by other experimenters. From this the authors 

 conclude that for small distances magnetic resistance of air is 

 proportional to length. When the magnetising current was 

 passed round the one half of the divided ring on which the test 

 coil was wound, a greater induction could be obtained than by 

 any other way of magnetising, and this the authors do not 

 attempt to explain. Mr. Bosanquet said he had alw.ays found 

 greater inductions obtainable in the middle of bar electro- 

 magnets or open magnetic circuits, than could be produced in 

 closed magnetic circuits, and thought the above observations 

 confirmed his own results. A discussion followed in which Mr. 

 C. V. Boys, Mr. W. M. Mordey, iVIr. Bosanquet, and Prof 

 Perry took part. — On account of the late hour the reading of a 

 note on dynamo machines and motors, by Profs. Ayrton and 

 Perry, was postponed till the next meeting. 



Zoological Society, March 15. — Dr. St. George Mivart, 

 F. R.S., Vice-President, in the chair. — The Secretary read a 

 report on the additions that had been made to the .Society's 

 menagerie during the month of February 18S7. — Mr. Howard 

 Saunders exhibited a young male Harlequin Duck (Cosmone/ta 

 hisiriouica), shot off the coast of Northumberland on December 

 2 last, and remarked that it was the second authentic British- 

 killed specimen in existence. — Mr. Oldfield Thomas read a paper 

 on the Bats collected by Mr. C. M. Woodford in the Solomon 

 Islands. — A communication was read from Mr. W. R. Ogilvie 

 Grant, containing an account of the birds collected by Mr. C. 

 M. Woodford at Fauro and 'Shortland Islands, in the Solomon 

 Archipelago, and in other localities of the group. — A communi- 

 cation was read from Mr. G. A. Boulenger, containing a second 

 contribution to the herpetology of the Solomon Islands. — Mr. 

 Oldfield Thomas re.ad a paper describing the m.iIk-dentition of 

 the Koala [Pnascolarctos cinercus), which was shown to be in 

 the same state of reduction as had been described by Prof 

 Flower in the case of the Thylacine. — A second communication 

 from Mr. Boulenger contained a description of a new Gecko of 

 the genus Chondyodactyhis from the Kalahari Desert, South 

 Africa, based on a specimen which had been presented to the 

 Natural History Museum by Mr. J, Jenner Weir. The author 

 proposed to call it C. weiri. 



Geological Society, March 9.— Prof. J. W. Judd, F.R.S. 

 President, in the chair. — The following communications were 

 read: — On Chondrostcits acipenseroides, Ag., by Mr. James W. 

 Davis. — On Aristosuchus pusillus, Ow. , being further notes on 

 the fossils described by Sir R. Owen as Poikiloplairon pusillus, 

 Ow. ; on Patricosaiirus merocratus, Seeley, a lizard from the 

 Cambridge Greensand, preserved in the Woodwardian Museum 

 of the University of Cambridge ; on Hetcrosiichus valdensis, 

 Seeley, a procoelian crocodile from the Hastings Sands of 



