546 



NA TURE 



[April 9, 1885 



which the centre conducting plate was of copper, iron, and 

 carbon respectively ; but the general effects were practically the 

 same as when platinum was used. The currents (from Faure- 

 Sellon-Volckmar cells) were increased gradually, the effects of 

 each increase being carefully noted. The nature and resistance 

 of the rarified space in the shunt-circuit had to be ascertained. 

 Certain increments in the current were followed by a diffused 

 blue effect in the globe, more or less intense, accompanied in 

 each instance by a marked fall in the resistance of the shunt — 

 pointing to an intimate connection between the two phenomena. 

 The strength of the shunt-current when the faint blue tinge ap- 

 peared was : with carbon, 3'42 ; with iron, 3^85 ; and with cop- 

 per, 3'8o milliamperes. No perceptible difference in the results 

 was observable with lamps in which the centre plate was a fine 

 wire or a very broad surface, nor when the plates were doubled. 

 That the effect was due primarily to the " Crooke's bombard- 

 ment," or the projection of molecules in right lines from the 

 carbon filament on to the metal plate was confirmed by the 

 following experiments : — Lamps were constructed varying the 

 position of the plate. In one the plate, was fixed at the end of 

 a tube having a portion of the filament exposed to the plate ; in 

 this case, with an E.M.F. of 108 volts in the main circuit, the 

 blue effect entered the tube. In another lamp the tube was so 

 constructed that no portion of the filament was opposed by right 

 lines to the metal plate ; with 1 12 volts the blue in the globe 

 became very marked ; with 120 volts the bulb was hot, the tube 

 cool. Another lamp was constructed with three branches at 

 right angles to each other, and each metal plate taken in suc- 

 cession ; no result was obtained, no current being evident in 

 either section. All the experiments went to show that, when 

 once the blue effect appeared, destruction was only a question of 

 time. Hence this blue effect is an indication of the advent of 

 disintegration, and a very useful warning of danger ahead. 

 Whenever the incandescence of the filament is raised beyond a 

 certain limit, the interior of the glass envelope is blackened by 

 a layer of carbon which has been deposited by a Crooke's bom- 

 bardment effect. 



It was evident from the observations that the Edison effect is 

 due to the formation of an arc between the carbon filament and 

 the metal plate fixed in the vacuous bulb, and that this arc is 

 due to the projection of the carbon particle in right lines across 

 the vacuous space. Its presence is detrimental to the life of the 

 lamp, and as its appearance is contemporaneous with the blue 

 effect, the latter is a warning of the approach of a critical point 

 and a sure indication that the E.M.F. is dangerously high. It 

 is also clear that, as the Edison effect is only evident when we 

 are "among the breakers," it is not available for practically 

 regulating the conditions of electric light currents as its ingenious 

 discoverer originally proposed. 



Mathematical Society, April 2. — J. W. L. Glaisher, 

 F.R.S., President, in the chair.— Dr. R. Stawell Ball, F. R.S., 

 Astronomer Royal, Ireland, and Baboo Basu, of Bhowanipore, 

 were elected Members. — The following communications were 

 made : — New relations between bipartite functions and deter- 

 minants, with a proof of Cayley's theorem in matrices, by Dr. 

 T. Muir. — On eliminants, and associated roots, by E. B. Elliott. 

 — On five properties of certain solutions of a differential equation 

 of the second order, by Dr. Routh, F.R.S. — On the argu- 

 ments of points on a surface, by R. A. Roberts. — On congruences 

 of the third order and class, by Dr. Hirst, F.R.S. 



Geological Society, March 11. — Prof. T. G. Bonney, 

 D.Sc, LL.D., F.R.S., President, in the chair.— William 

 Lester and Thomas Stewart were elected Fellows of the Society. 

 — The following communications were read : — The granitic and 

 schistose rocks of Donegal and some other parts of Ireland, by C. 

 Callaway, D.Sc, F. G. S. The author first recalled attention 

 to the current theories on the nature of the Donegal granitic 

 rock, one which described it as a highly metamorphosed portion 

 of a sedimentary series, another which regarded it as a mass of 

 Laurenrian gneiss. Tn his view, however, it was a true igneous 

 granite, posterior in age to the associated schists. In six dis- 

 tricts examined it was intrusive and sent out veins. The apparent 

 interstratification with bedded rocks was explained as a series of 

 comparatively regular intrusions. Where the granite was seen 

 in contact with limestone, the latter contained garnets and other 

 accessory minerals. No gradation could be discovered between 

 the granite and any other rock, the junctions (even in the case 

 of small fragments of schist immersed in granite) being well 

 marked. The granite was distinctly foliated. In some localities 



there was merely a linear arrangement of the mica ; but near 

 the western margin of the granite promontory there was a 

 striping of light and dark bands, the colour of the latter being 

 due to the abundance of black mica. The gneissic structure was 

 attributed to lateral pressure, the existence of which in the 

 associated strata was seen in the conversion of grits into schist-like 

 rocks, in the production of cleavage in beds of coarse materials, 

 in the crushed condition of some masses, in the overthrow of 

 folds, and in the production of planes of thrust. The direction 

 of the pressure was perpendicular to the planes of foliation in 

 the granite. The schistose rocks of the region were divided into 

 two groups. The Lough Foyle series consisted of quartzites, 

 quartzose' grits with a mineralised matrix, slaty-looking schists, 

 fine-grained satiny schists, black phyllites,3and crystalline lime- 

 stones and dolomites. The semicrystalline condition of most of 

 these rocks was characteristic. This series was well seen at London- 

 derry and on Lough Foyle, and formed a broad band striking to 

 the south-west. These rocks were compared with similar types in 

 the Hill of Howth (north of Dublin), near Aughrim (Co. Wick- 

 low), and south of Wexford. The Leinster semicrystalline 

 masses were quite unlike the Wicklow Cambrians, and bore a 

 strong resemblance to the slaty series of Anglesey. They were 

 lithologically intermediate between -the Donegal and Anglesey 

 groups, and from a comparison of all these areas the author re- 

 ferred the Lough Foyle series, with some confidence, to the 

 Pebidian system. The prolongation of the Lough Foyle rocks 

 into the Grampian region was well known, and Ireland thus 

 served to connect some parts of the Scottish highlands with 

 South Britain. The author was not prepared to correlate this 

 Donegal series with any American group, but the lithological 

 affinities were rather with the Taconian that with the Huronian. 

 The Kilmacrenan series, in which the granite is intrusive, was 

 described as crystalline, and older than the Lough Foyle group. 

 It was mainly made up of micaceous, quartzose, hornblendic, 

 and hydromagnesian schists, quartzites, and crystalline lime- 

 stones. There were no indications in these rocks of a meta- 

 morphism progressive in the direction of the granite. This series 

 was lithologically similar to the Montalban system. Fifty-five 

 microscopic slides of Donegal and Leinster rocks had been 

 examined by Prof. Bonney, whose observations confirmed those 

 of the author both as regards the nature and relations of the 

 granite and the general characters and state of crystallisation of 

 the two schistose groups. — On hollow spherulites and their 

 occurrence in ancient British lavas, by Grenville A. T. Cole, 

 F.G.S. 



Edinburgh 



Royal Society, March 2. — Robert Grey, Vice-President, in 

 the chair. — At the request of the Society's Council, Dr. A. 

 Geikie, Director-General of the Geological Survey, gave an 

 address on the recent progress of the Survey. He indicated 

 what would be the future work of the Survey. 



March 16. — Thomas Stevenson, M.I.C.E., President, in the 

 chair. — Prof. Tait called attention to anticipations of the kinetic 

 theory, and of synchronism, which occur in a trac t, " De 

 Potentia Restitutiva," published by Hooke in 167S. — Prof. 

 Cram Brown read a paper on the hexagonal system in crystallo- 

 graphy. The forms of the uniaxial systems may be regarded as 

 derived from forms or parts of forms or combinations of the 

 regular system by uniform expansion or contraction in a direc- 

 tion parallel to the axis of the uniaxial system, i.e. normal to a 

 face of the cube for the tetragonal, and normal to a face of the 

 octahedron for the hexagonal system. Faces, therefore, which 

 are, in the regular form or combination, at right angles to or 

 parallel to such axis, retain their relative angular position un- 

 changed in the uniaxial form or combination, and can be 

 represented by means of indices referring to the rectangular axes 

 of the regular system, whatever be the amount of the deforma- 

 tion (expansion or contraction). These faces are prism faces, 

 parallel to the axis, and basal faces at right angles to it. All 

 other faces have their angular position affected by the deforma- 

 tion. These other faces are pyramid faces. Each pyramid face 

 lies between, and in the same zone with, a prism face and a basal 

 face. It may, therefore, be represented by the symbol 



as + -l>t, where s and t are the symbols of the prism face 



P 

 and the basal face respectively, a and h are small whole numbers, 

 and p is the ratio of the length of a line parallel to the axis after, 



to the length of the line before deformation. We may put - = 11, 



