]66 



NA TURE 



[June 14, 1906 



eastern sides, giving rise to at least three important streams 

 of lava. Another rift, to the north-north-east of the cone, 

 emitted lava that forms an apron on that side of the 

 mountain, and must, of course, have been formed early 

 in the eruption, that is, before April 7 to 8. The ejected 

 blocks are chiefly old lavas and scoria, partly re-cooked 

 and metamorphosed, with their cavities filled by tachylytic 

 juice from the fluid magma of the neighbouring chimney. 

 The cavities are also often lined by sublimations of augite, 

 hornblende, leucite, microsommite, haematite, halite, and a 

 well-crystallised, yellow, deliquescent mineral which proves 

 to be a new chloride of manganese and potash for which 

 a new mineral name is proposed. A few fragments of 

 limestone, and the various mineral aggregates derived by 

 metamorphism from it, are met with, but they are chiefly 

 re-ejected old ejected blocks. A light green spongy tachy- 

 lyte is also frequent. The "essential ejecta," either as 

 scoria or lava, does not show any marked difference from 

 the usual products of Vesuvius in such eruptions during the 

 last three centuries. Although much damage has been 

 done, great areas of rugged lava-surfaces that would have 

 required centuries to render cultivable are now available 

 for the growth of woods, vines, and herbaceous plants. 



Physical Society, Mav 25. — Dr. C. Chree, F.R.S., vice- 

 president, in the chair. — Colour phenomena in photometry : 

 J. S. Dow. The author has found that to compare lights 

 of different colours is chiefly a matter of practice. The 

 central portion of the retina is more sensitive to red, and 

 less sensitive to green, than the surrounding portion. 

 When an attempt to photometer lights of different colour 

 is made, differences are found as the distance of the eye 

 from the photometer-screen is altered, and different results 

 are obtained with different photometers. Differences of 

 5 per cent, can easily be obtained. The Purkinje pheno- 

 menon, generally regarded as a cause of uncertainty in 

 ordinary work, only becomes noticeable at small illumin- 

 ations and with large fields of view. E.xperiments are 

 described to show that flicker photometers seem to be 

 affected by colour-phenomena, but to a smaller extent than 

 ordinary ones. Whether flicker or an ordinary photometer 

 is adopted, it is necessary to specify the size of the field, 

 the distance of the eye, and the order of illumination used 

 in order to get consistent results. — Automatic arc-lamp : 

 H. Tomlinson and G. T. Johnston. A simple form of 

 automatic arc-lamp. A vertical brass tube supported by 

 a wooden framework carries the upper carbon, which can 

 be raised or lowered by hand and clamped in any position 

 in the tube. The lower carbon fits into a hollow brass 

 tube, and into the lower part of the tube is fitted an iron 

 plunger. The plunger is surrounded by a solenoid, con- 

 sisting of a layer of No. 14 copper wire, the internal 

 diameter of the solenoid being slightly greater than the 

 diameter of the plunger. The plunger dips into a box of 

 mercury, and is made to float upright by means of a brass 

 collar and by the rounded ends of three nails forming an 

 equilateral triangle. The current enters the upper carbon 

 through the brass cylinder, passes through the lower carbon 

 into the mercury, and then through the solenoid. To 

 " strike the arc " the lower carbon is raised to touch the 

 upper one, and the plunger is then permitted to sink into 

 the mercury until the suction of the solenoid balances the 

 buoyancy of the mercury. — The theory of moving coil and 

 other kinds of ballistic galvanometers : Prof. H. A. 

 Wilson. The exact formulae giving the quantity of elec- 

 tricity passed through various types of ballistic galvano- 

 meters in common use are obtained. The various types 

 require different formulas, all of which reduce to the same 

 formula when the angle of deflection is small. In the case 

 of a moving-coil galvanometer with rectangular coil, iron 

 core, and pole-pieces arranged so as to give a radial mag- 

 netic field, the formuU-E take a simple form. — Bifilar 

 galvanometer free from zero creep : A. Campbell. For 

 ni'asuring direct currents and voltages of ordinary range 

 moving-coil galvanometers are convenient. The usual 

 instruments are affected by gradual displacement of zero 

 Avhen a deflection is maintained for some time. This diffi- 

 culty is got over by replacing the torsional suspension by 

 a bifilar .system with two wires so far apart that the gravity 

 control swaiTips that due to the torsion of the wires. The 

 wires are more than i cm. apart, and the scnsitiviiv with 



40 ohms resistance is 40a mm. at i metre for 0001 ampere. 

 The full deflection may be maintained for hours without 

 causing a zero creep of i part in 2000. To attain good 

 damping a powerful magnet is used. 



Zoological Society, May 29. — Mr. Frederick Gillett, vice- 

 president, in the chair. — Mammals collected by Mr. 

 C. H. B. Grant in the Zoutpansberg district of the Trans- 

 vaal, and presented to the National Museum by Mr. C. D. 

 Rudd : H. Schwann and O. Thomas. The collection was 

 obtained at two localities — Klein Letaba at 1000' altitude 

 and Woodbush at 4500' — and so gave a good general 

 idea of the fauna of the region. In all it consisted 

 of about 250 specimens belonging to fifty-one species and 

 subspecies, of which several were described as new. In 

 addition, the old genus Macroscelides was broken up into 

 three, the new name Elephantulus being given to the group 

 of which M. rupestris was the type, and Nasilio to that 

 typified by M. brachyrhynchus. — The vascular system of 

 Heloderma, with notes on that of the monitors and croco- 

 diles : F. E. Beddard. — The external characters of an 

 unborn foetus of a giraffe (Giraffa caiiiclopanlalis 

 antiquorum rf X G. c. laardi ' 'i) : F. E. Beddard. — The 

 South .African dinplosaurian reptile Howesia : Dr. R. 

 Broom. 



Dt'lil.lN. 



Roval Irish Academy, May 14. — Dr. F. A. Tarleton, 

 president, in the chair. — Some applications of Bessel's 

 functions to physics : Prof. F. Purser. In this paper the 

 author applies (i) the Besselian forms K„(nr) sin, cos 112 

 and !„(»!»•) (sin /;, cos h 1-112), where K„()!»-) = J„(<)ir), to the 

 solution of problems of electric potential, viz. the finit' 

 Leyden jar and equal circular disks fronting one another 

 at different potential, the theory of the condenser formed 

 by a circular disk midway between two large circular 

 plates, and of the guard-ring electrometer. (2) The same 

 functions are applied to some problems in fluid motion. 

 (3) Certain problems in the theory of the elastic equilibrium 

 of a right circular cylinder are discussed bv the use of the 

 Besselian forms 



J] ""' 



sin /;, cos h, 1112 ), 



Kj 



("' 



sm, cos «/■ 



J,(.v)= -'l^).i-^), K,(,v)=|l(K„(.v). 



NO. tgi I, VOL. 74] 



(4) Lastly, the functions ]„(mr), ],(""■) are applied to 

 some problems of vortical motion of fluids under the in- 

 fluence of viscosity. — .\ map showing the relative distribu- 

 tion of various types of rock on the sea-floor off the west 

 of Ireland, based on materials dredged by the Fishery 

 Survey of the Department of Agriculture for Ireland : Prof. 

 Cole. It is proposed to publish further details in the 

 report of that survey, but meanwhile it is believed that the 

 stones show the actual local distribution of rocks on sunken 

 land, and are not the result of casual drift. The Porcupine 

 Bank undoubtedly consists of a mass of olivine-gabbro, 

 while a Carboniferous area west of CO. Galway indicates 

 that Connemara may have risen as an island in the 

 Carboniferous sea. 



Royal Dublin Sociuy, May 15. — Pror. J. A. McClelland 

 in the chair. — Injurious insects and other anim'als observed 

 in Ireland during 1905 : Prof. G. H. Carpenter, In 

 addition to records of several well-known farm and orchard 

 insects, the paper contains an account of the rare " cauli- 

 flower " disease of the strawberry, due to the small nema- 

 tode worm Aphelenchus fragariae, J. R. Bos, observed in 

 county Wicklow. — A possible connection between the recent 

 disturbances at Vesuvius and San Francisco : Rev. H. V. 

 Gill. This paper contained an account of some experi- 

 ments with rotating bodies, and an application of the prin- 

 ciples involved to certain seismic phenomena. A hollow 

 tee-totum weighted at one point will not spin about its 

 axis of symmetry, but if it contain matter capable of shift- 

 ing its position, it will automatically tend to steady itself, 

 owing to the symmetrical distribution of the movable 

 matter round its circumference. For example, if three 



