June 29, 1905J 



NA rURE 



215 



SOCIETIES AND ACADEMIES. 



London. 



Geological Society, June 7.— Dr. J. E. Marr, F.R.S., 

 president, in the chair. — The microscopic structure of 

 minerals forming serpentine, and their relation to its 

 history ; Prof. T. G. Bonney and Miss C. A. Raisin. 

 The authors embody their investigations in the following 

 conclusions : — (i) That both a tint and pleochroism are 

 accidental rather than essential characteristics of antigorite. 



(2) Neither are low polarisation-tints characteristic, unless 

 two mica-like minerals e.xist, otherwise indistinguishable. 



(3) That it is doubtful whether any hard and fast line can 

 be drawn between antigorite and the more fibrous forms 

 in ordinary serpentine rocks. (4) That the most typical 

 antigorite appears when the rock has been considerably 

 affected by pressure, but it becomes less so when the latter 

 has been very great. (5) That so far from the nearly 

 rectangular cleavage of augite originating the " gestrickte 

 struktur, " it is worse preserved than any other original one 

 in the process of serpentinisation. Typical antigorite, how- 

 ever, apparently is rather more readily produced from 

 augite than from the other ferromagnesian silicates, but 

 is more directly a consequence of pressure than of chemical 

 composition. — The tarns of the Canton Ticino : Prof. E. J. 

 Garwood. The lakes dealt with comprise the larger 

 .Alpine tarns which occur in the Canton Ticino. Most of 

 these drain into the Ticino basin ; one or two, however, 

 flow into the Reuss or the Rhine. These lakes owe their 

 origin, when they are rock-basins, to the presence of lines 

 of weakness, along which in many cases solution has taken 

 place, while in some shallow tarns ice may have removed 

 detached fragments ; but in no case has a lake been found 

 which can reasonably be assigned to ice-excavation inde- 

 pendent of rock-structure. 



Mineralogical Society, June 14. — Prof. If. A. Miers, 

 F.R.S., president, in the chair. — The chemical composi- 

 tion of lengenbachite : A. Hutchinson. A quantitative 

 analysis of the new mineral from the Binnenthal recently 

 described by Mr. R. H. Solly leads to the formula 

 7PbS.2As,S3, part of the lead being replaced by silver and 

 copper, and part of the arsenic by antimony. — The 

 chemical composition of hutchinsonite : G. T. Prior. 

 Chemical examination of this new and extremely rare 

 mineral from the Binnenthal described by Mr. R. H. Solly 

 showed that it could be added to crookesite and lorandite 

 as a third mineral containing the rare element thallium 

 as an important constituent. Quantitative analysis, made 

 on a small amount of material (about 70 mg.), showed 

 the presence of about 20 per cent, of thallium, and 

 suggested the formula (Tl,Cu,Ag),S.As,Sj + PbS.As,S,. 

 — The identity of the amiantos of the ancients with 

 chrysotile : Dr. J. W. Evans. The principal source of 

 amiantos appears to have been Cyprus. Specimens brought 

 by Prof. Wyndham Dunstan from the ancient workings on 

 the slopes of Mount Troodos prove to be chrysotile, and 

 not tremolite asbestos. A chemical analysis by Mr. G. S. 

 Blake confirmed this result. — Gnomonic projection on two 

 planes at right angles : Dr. J. \V. Evans. By means of 

 these projections and the rotation of one plane on an 

 axis at right angles to the other, simple solutions of 

 crystallographic problems are obtained. — The President 

 exhibited supersaturated solutions of sodium nitrate show- 

 ing the transition from the metastable condition, in which 

 crystallisation is only possible in the presence of solid 

 crystals, to the labile condition, in which the liquid can 

 crystallise spontaneously. 



Physical Society, June 16. — Prof. J. H. Poynting, 

 F.R.S., president, in the chair. — On the ratio between the 

 mean spherical and the mean horizontal candle-power of 

 incandescent lamps : Prof. Fleming;. This paper contains 

 a theoretical deduction from first principles of experimental 

 results given bv Mr. G. B. Dyke in a paper read before 

 the Physical -Society on November 11, 1904, respecting the 

 ratio of the M.S.C.P. of incandescent electric lamps to 

 the M.H.C.P. taken when the lamp was rotating round a 

 vertical axis. In the case of nine different types of electric 



NO. 1 86 1, VOL. 72] 



glow-lamps, this ratio was found to be a number near 

 0-78. The author shows, by discussing the simple case of 

 linear filament, that the ratio of the M.S.C.P. to the hori- 

 zontal candle-power for this last case must be represented 

 by the value 7r/4 = o-785, and hence that the constant ratio 

 found experimentally by Mr. Dyke necessarily follows as 

 a simple consequence of the fact that the light sent out 

 in any direction from each unit of length of an incandescent 

 filament varies as the cosine of the angle of inclination 

 of the ray to the normal to the filament. In the paper it 

 is shown also how a simple correcting factor may be 

 obtained for reducing the actual horizontal candle-power 

 of a linear filament of finite length to the candle-power in 

 the same direction which would be found if the elements 

 of the filament were concentrated on the axis of the photo- 

 meter and all normal to it. — The electrical conductivity of 

 flames : Dr. H. A. Wilson. The paper contains an account 

 of a series of experiments on the conductivity of a coal-gas 

 flame for electricity between platinum electrodes immersed 

 in the flame. The variation of the current with the dis- 

 tance between the electrodes and the fall of potential along 

 the flame are investigated by using a special burner pro- 

 ducing a long narrow flame. The burner consists of a 

 fused quartz tube with a series of small holes parallel to 

 its diameter. The electrodes are two parallel discs of 

 platinum, one fixed at one end of the flame, and the other 

 capable of movement horizontally in the flame, so that it 

 can be placed at any desired distance from the fixed 

 electrode. The current through the flame was measured 

 by a moving coil galvanometer, and the potential difference 

 between the electrodes by an electrostatic voltmeter. The 

 quartz-tube burner being a good insulator enables a current 

 to be passed from one end of the flame to the other without 

 fear of any of it going through the tube instead of through 

 the flame. It thus enables the effect of putting salts into 

 different parts of the flame to be easily studied. — Contact 

 with dielectrics : Rollo Appleyard. Among the conclusions 

 arrived at are the following : — (a) Except in the case of 

 homogeneous dielectrics, it is misleading to deduce specific 

 values referred to unit cube of the material from the 

 results of tests on sheets, (b) With tin-foil electrodes, the 

 apparent resistance of press-spahn diminishes as the load 

 increases, and it attains a fairly constant value at a load 

 of 400 grams per cm.', (c) If, with tin-foil electrodes, the 

 load is gradually diminished after a load of 543 grams 

 per cm.", the resistance gradually rises, but the rise is 

 less rapid than the diminution in the former case (b). 



(d) When the full load with tin-foil electrodes is again 

 restored the resistance falls to its minimum value. 



(e) For small loads, with tin-foil electrodes, the 2nd-minute 

 deflection is in general greater than the ist-minute de- 

 flection. As the load increases, a point is reached at which 

 these deflections become approximately equal. For loads 

 greater than about 360 grams per cm.-, the ist-minute 

 deflection is in general greater than the 2nd-minute de- 

 flection. (/) Increase of voltage, with tin-foil electrodes, 

 especially with small loads, behaves like increase of load, 

 apparently increasing the contact area, and diminishing 

 the observed dielectric resistance. Load, voltage, and the 

 normal effect of " absorption " thus combine to determine 

 the ratio of the ist-minute deflection to the 2nd-minute 

 deflection, (g) When mercury electrodes are used, the 

 dielectric-resistance, as measured at different voltages, is 

 sensibly the same, even for abrupt and great changes of 

 voltage. (/?) When mercury electrodes are used, the 

 2nd-minute deflection is in general never greater than the 

 ist-minute deflection. The inference is that when, with 

 tin-foil electrodes, the converse is the case, it arises from 

 imperfect contact, and not from the material itself, 

 (i) When mercury electrodes are used, the dielectric- 

 resistance, as measured with a voltage applied in a given 

 direction, is sensibly the same as that measured with the 

 voltage reversed, and this equality appears to becoine 

 greater after a few reversals. (;') There is a critical load 

 at which . tin-foil electrodes yield fairly accurate results. 

 With greater loads there is danger of crushing the material. 

 With a less load the contact is faulty. — The pendulum 

 accelerometer ; an instrument for the direct measurement 

 and recording of acceleration : F. Lanchester. — A new 

 form of pyknometer : N. V'. Stanford. 



