March 6, 1879 J 



NATURE} 



427 



Fane, Benjamin Neeve Peach, were elected Fellows of the 

 Society. — The President announced the receipt of a legacy of 

 1,000/. bequeathed to the Society by the late Sydney Ellis, Esq., 

 of The Park, Nottingham. — The following communications 

 were read : — On the occurrence of pebbles with Upper-Ludlow 

 fossils in the lower carboniferous conglomerates of North Wales, 

 by Aubrey Strahan, F.G.S., and Alfred O. Walker, F.L.S. 

 The authors described the mode of occurrence near Abergele of 

 certain lower carboniferous conglomerates, best exposed in 

 Ffemant Diogle, and especially of one containing numerous 

 red and green sandstone pebbles, which inclose fossils of Upper- 

 Ludlow forms, and lying above the so-called "bastard lime- 

 stone." From the arrangement of the beds the authors believe 

 that they may have been deposited against a bank or sloping 

 surface of Wenlock shale ; and they state that the great majority 

 of the pebbles in the conglomerate are quite unlike any rock 

 known in the district, but closely resemble the Upper-Ludlow 

 beds of Kendal and Central Wjdes. The authors discuss the 

 origin of the pebbles, and suggest "the probable extension of 

 the Ludlow beds under Lancashire as the most likely source 

 from which they can have been derived." — On a new griup of 

 pre-Cambrian rocks (the Ar\onian) in Pembrokeshire, by Henry 

 Hicks, F.G.S. ; with an appendix on their microscopic structure 

 by T. Davies, F.G.S. In some new areas of pre-Cambrian 

 rocks, discovered by the author last summer in Pembrokeshire, 

 some rocks of a character hiiherto unrecognised in this country 

 were made out. As they were found to hold there, and subse- 

 quently also in other areas, a very definite stratigraphical 

 position, with a vertical thickness of several thousand feet, they 

 have been separated by the author from the other pre-Cambrian 

 groups under the distinctive name of Arvonian. They were 

 also found to occupy an intermediate position between the 

 Dimetian and Pebidlan formations, and at all points, so far as 

 could be made out, appeared to be separated from each of those 

 formations by stratigraphical breaks. The new areas where they 

 are chiefly exposed are situated some few miles to the north of 

 Haverfordwest, where they form ridges running in a direction 

 from north-east to south-west. They occupy an average width of 

 about a mile, attain at some points to a height of nearly 600 feet, 

 and together have a length of over nine miles. The rocks are 

 flanked by Pebidian and Cambrian beds along their north-west 

 borders, and on the south-east Silurian rocks have been brought 

 against them by faults. In general appearance, as well as in 

 their more minute lithological characters, they are easily distin- 

 guished from any of the rocks hitherto described by the author 

 as characteristic of the Dimetian and Pebidian groups in Pem- 

 brokeshire. They are, however, so closely allied to some of the 

 true "halleflinta" rocks of Sweden, that it seems to the author 

 and Mr. Davies that this is the name that should be applied to 

 them in a petrological sense. The author and Mr. Da\'ies 

 believe the origin of the rock to have been a sedimentary one. — 

 On the pre-Cambrian (Dimetian, Arvonian, and Pebidian) rocks 

 of Caernarvonshire and Anglesey, by Henry Hicks, F.G.S.; 

 with an appendix on their microscopic structure by the Rev. 

 Prof, T, G. Bonney, F.R.S. In this paper the author gave the 

 results of some further researches made in Caemar\-onshire and 

 Anglesey since his previous communication to the Society on 

 December 5, 1877. -A- brief statement of some of the results 

 was read at the last meeting of the British Association in Dublin ; 

 much additional evidence was now brought forward, besides 

 y important facts obtained since by microscopical examina- 

 ii-.i of the rocks. — On the quartz -felsite and associated rocks at 

 the base of the Cambrian series in north-western Caernarvon- 

 shire, by the Rev. Prof. T. G. Bonney, F.R.S. The great 

 masses of quartz-felsite (or quartz- porphyry) which occur in the 

 vicinity of Bangor, Caemar\'on, and Ll3m Padarn, are coloured 

 ae Survey map as intrusive, and in the memoir r^;arded as 

 probably the result of an extreme metamorphosis of the 

 ij..erbeds of the Cambrian series. The author showed that 

 these quartz-felsites exhibited, in places, all the characteristics 

 of true igneous rocks. — On the metamorphic series between 

 Twt Hill, Caernarvon, and Port Dinorwic, by the Rev. Prof. T. 

 G. Bonney, F.R.S., and F. T. S. Houghton, B.A. In the Geo- 

 ioaJ Sun-ey map this district is coloured as " intrusive felsite," 

 •-her with those sjwken of in the last paper. It was asserted 

 e probably metamorphic rock by Prof. Hughes and Dr. 

 -ks in a communication made to the Society last year, and 

 rirst author confirmed that view by microscopic examination 

 specimen collected by them. The authors had during the 

 : autumn more minutely examined the district, and found : 



I. That the general character of the series was that of a meta- 

 morphic one ; 2. That the rocks of granitoid aspect were asso- 

 ciated with well-marked beds of conglomerate ; 3. That this 

 series extended up to a little beyond Port Dinorwic, where the 

 quartz-felsite set in. The paper described the microscopic 

 structure of some of the rocks, and the author expressed the 

 opinion that the more granitoid specimens were probably the 

 results of alterations of felspathic grits. 



Physical Society, February 22. — Prof. W. G. Adams, in 

 the chair. — New Members : Rev. Coutts Trotter, Prof. G. D, 

 Living, T. C. Adam^, F. W. Paterson. — Dr. C. W, Siemens 

 described his new electric current regulator. A necessary con- 

 dition of the transmission of power to a distance by electricity 

 along a single conductor and re-distributing it by means of 

 branch circuits to separate electric lamps or motors, is that the 

 current strength in each lamp shall be practically uniform. Other- 

 wise the current flowing in the whole branch varies. Hence the 

 necessity of a regulator to regulate the flow of current so as to 

 keep it uniform, however the resistance of the circuit or the elec- 

 tromotive force of the source may vary. The author believes 

 that by properly arranging a nimiber of dynamo-electric ma- 

 chines, either in series or parallel (for intensity or quantity), at 

 each end of the wire, a vast amount of power may be sent along 

 a small copper conductor successfully, provided the distribution 

 is properly regulated. He has designed a regulator based on the 

 heating of a wire by the passage of a current through it. A fine 

 strip of mild steel ^V^™- thick is stretched horizontally between 

 two terminals. An upright spindle is supported by means of an 

 insulating foot, upon the middle of this strip, in such a manner 

 that, as the strip bends or sags by its expansion, the spindle 

 sinks with it. Now this spindle carries at its top a table or 

 plate of metal (or, as the case may be, a set of radial springs), 

 and as the spindle rises or sinks to different heights, this plate or 

 these springs make contact with other springs set radially round ; 

 and these contacts take out from or throw in resistance coils 

 into the circuit of the current. The sensitive strip is so thin 

 that it may be regarded as a radiating surface merely, 'and 

 it may be assumed that its temperature, due to heating by the 

 current, balances itself with the radiation instantaneously. 

 After passing through the steel strip, the current flows through 

 the coils thrown into circuit, and, by the arrangement we have 

 described, if the current increase so as to over-heat the strip, 

 the latter sags a little more, the spindle sinks, and the conse- 

 quence is that one or more of the spring contacts is broken, 

 and one or more coils inserted in circuit A rise of 1° F. in 

 the temperature of the strip is sufficient to liberate two or three 

 of these coils. The fact that the temperature of the strip varies 

 as the square of the current, favours the sensibility of the appa- 

 ratus. An older form of this apparatus, ha\Tng pendulDtis con- 

 tacts, was also shown ; also a regulator in which the expansion 

 by heating of a sensitive wire caused the resistance of several 

 carbon buttons in contact to vary through the pressure exerted 

 on them by means of a bell-crank lever. Dr. Siemens had not 

 been able to prepare carbons which gave the wide variations 

 of resistance obtained by Mr. Edison. Siemens' regulator can 

 also be used as a current meter by causing the sensitive strip 

 to actuate a lever carrying at its end a pencil writing on a 

 moving paper. Dr. Coffin said that he had thought of a r^u- 

 lator in which the heating of a wire spiral in a gaseous chamber 

 would cause the gas to expand and drive up a mercury colunm 

 past a series of contacts which would throw resistances in circuit. 

 Dr. Guthrie suspected, from some experiments of his, that the 

 conductivity of conductors was not strictly proportional to their 

 sectional area. — Dr. Schuster then gave the results of some 

 observations of his on the spectrum of lightning. These were 

 made by a spectroscope with two prisms, one for the red and 

 the other for the blue end of the spectrum, which were shifted 

 into the line of sight by a chamber arrangement. Thre ? obser- 

 vations were made : one at Las Animas, one at Manitou, and 

 one at Salt Lake City last year. These showed the three nitro- 

 gen lines with three well-defined bands and one doubtfu band. 

 The nitrogen lines correspond to the spectrum of air. and the 

 bands appear to Dr. Schuster to agree with the spectrum of the 

 light round the negative pole of the sf^rk in a tube containing 

 oxygen with adulteration of carbonic oxide. — Prof. Ayrton then 

 exhibited an exisothermal model of a cooling globe, the globe 

 in question being a trachyte earth 8,000 miles in diameter. The 

 model gives graphically the temperature of everj- single part of 

 the cai\h. from the moment when it was at the temperatxire of 



