July 31, 1884] 



NA TURE 



33i 



Mr. John Home, F.G.S. — On the occurrence of Prehnite and 

 other zeolites in the rocks of Samson's Ribs and Salisbury 

 Crags, by Mr. Andrew Taylor. — On a new locality for zoisite 

 at Loch Garve, Ross-shire, by Mr. Hamilton-Bell. — On diatom- 

 aceous deposits in Scotland, by Prof. W. Ivison Macadam. 

 The author drew attention to the vast extent of some of these 

 beds, and gave particulars as to the proportions of silica, &c, 

 contained in them. The deposits were being worked up to 

 yield an absorbent for dynamite manufacture, and gave a 

 material having double the liquid retaining power of samples 

 of " kieselguhi " experimented on. — On the albertite beds of 

 Strathpeffer, Ross-shire, by Mr. Wm. Morrison. Mr. J. 

 Stuart Thomson referred to the fact that an allied jet mineral 

 was found embedded in the oil-yielding bituminous shales of 

 Midlothian. The substance only occurred in small quantities, 

 the largest pieces not exceeding a pound in weight. It is 

 capable of taking a fine polish, being similar to jet. In fact a 

 jet-worker pronounced it at first to be Spanisli jet. — On new 

 localities for kyanite in Glen Urquhart, Drumlach Glen, In- 

 verness-shire, and for staurolite at Presholme, Enzie, Banffshire, 

 by Mr. Thomas Walker. — On the crystallography of Bournonite, 

 by Mr. H. R. Miers, British Museum. The paper criticised the 

 history of the subject, and corrected various errors which have 

 crept into the earlier literature. To those crystallographic forms 

 hitherto recorded twenty-nine new forms are added as deter- 

 mined without doubt, and twenty-one as probable. A list of 

 over 1000 angles, calculated from the elements of Miller, is 

 given. The twinning (twin-plate the prism no) is dis- 

 cussed ; the observations of Hessenberg are supported, and it is 

 concluded that the twinning is always by juxtaposition, not by 

 interpenetration, but that Cornish crystals afford an example of 

 composition perpendicular to, as well as parallel to, the plane of 

 composition. — On a peculiar development of tourmaline from 

 Lockport, New York County, by Mr. R. H. Solly, F.G.S.— 

 Notes on the metallic veins of the Upper Hartz, Germany, by 

 Mr. H. M. Cadell. — Scottish localities for actinolites, by Mr. 

 Peyton. — On Welsh gold, by Mr. T. A. Readwin. A specimen 

 weighing 160 grains, from the Mawddach Valley, Merionethshire, 

 was exhibited. 



Dublin 



Royal Society, June 16. — Section of Physical and Ex- 

 perimental Science. — G. Johnstone Stoney, D.Sc, F. R. S., 

 Vice-President, in the chair. — The following papers were read 

 by Prof. G. F. Fitzgerald, M.A., F.R.S., Hon. Sec. :— (1) On a 

 nan-sparking dynamo. By applying the principles of Maxwell's 

 modification of Thomson's electrical doublet - to a dynamo in 

 which the current passes through two or more coils in parallel 

 circuit, it is possible to arrange the magnetic field and the 

 brushes so that when the terminals of any coil come into contact 

 with their brushes, the terminals shall be at the same difference 

 of potential as the brushes, and that when they break contact 

 there shall be no current running in the coil, thus avoiding all 

 sparking. The energy of self-induction usually wasted on local 

 currents and sparks will in this case be spent in producing useful 

 current. — (2) On dust repulsion. Prof. Osborne Reynolds's theory 

 of the action of the radiometer leads to the conclusion that a 

 very small body in dense gas is subject to similar forces as the 

 vanes of a radiometer in rare gas, and he made experiments which 

 showed that silk fibres in air at considerable pressures were sub- 

 ject to apparent repulsion by radiation : a similar action on dust 

 would explain the dust repulsion observed by Dr. Lodge. — (3) On 

 currents of gas on the vortex atom theory of gases. As the mo- 

 mentum of a simple ring vortex is not proportional to its velocity 

 and varies with its temperature, the momentum of a current of 

 vortex rings would do so too. This and the variations with 

 temperature of the velocity of sound and of the diffusion of gas 

 through small apertures all point to the conclusion that a simple 

 vortex ring is certainly too simple to explain the laws of material 

 atoms. A difficulty is raised as to the amount by which the 

 medium is carried forward by the translation and rotation of the 

 earth. — (4) On a method of studying transient currents by means 

 of an electrodynamometer. By comparing the initial swing of a 

 ballistic galvanometer which depends on S Cdtv/ith the initial 

 swing of an electrodynamometer which depends on 5 C 2 dt it is 

 possible in many cases to determine, in addition to the total 

 quantity of electricity that passes in the current, several matters 

 as to the distribution of the current during its time of passage. — 

 Prof. E. Hull, LL.D., F.R.S., on the' geological age of the 

 North Atlantic Ocean as bearing on the question of the per- 

 manency of continents and oceans. After referring to the views 



of those who hold the doctrine of " the permanency of oceans 

 and continents " as opposed to those who, with Lyell, hold that 

 continents and oceans have been interchanged during the past 

 history of the globe, the author proceeded to consider how the 

 formation of the North Atlantic Ocean might be adduced in 

 support of one or other of these views. Remarking that this 

 ocean was the only one at present known which could be used 

 in evidence, inasmuch as we were in possession of sufficient 

 knowledge of the geological structure of the regions by which it 

 is bounded to the east and to the west, he proceeded to show 

 how the distribution of the Silurian and Carboniferous rocks of 

 North America, on the one hand, and of the British Isles and 

 Western Europe on the other, pointed to the existence of the 

 derivative lands in the direction of the Atlantic Ocean during 

 these periods. In each case it was shown, by reference to details, 

 that the sedimentary portions of these formations swell out 

 towards the borders of the ocean, and tail out or become attenu- 

 ated towards the interior of the continents in the opposite direc- 

 tions. From this it was inferred that the lands from which the 

 sediment was derived occupied the region now overspread by 

 the ocean ; and, considering the great thickness of the sedi- 

 ments of these formations, the derivative lands were inferred to 

 be of continental proportions. An additional argument in support 

 of this view was also adduced from the distribution of the cal- 

 careous with the sedimentary deposits ; for it was shown that the 

 calcareous deposits (which were in the main of marine organic 

 origin) swell out and sometimes replace the sedimentary de- 

 posits, as we recede from the borders of the ocean on either 

 hand. From these consideration, the author concluded that 

 down to the close of the Carboniferous period the North 

 Atlantic was for the most part in the condition of a continent, 

 while the regions of Central and Eastern America, and of the 

 British Isles and Western Europe, were submerged under 

 oceanic waters. After this period, however, the relations were 

 altered. With the upheaval of the Alleghanies at the close of 

 the Falreozoic epoch, and with the terrestrial movement which 

 at the same time affected the Carboniferous and older rocks of 

 the British Islands and Western Europe, the Atlantic continent 

 was converted into an ocean, in which condition it has remained 

 to a great degree ever since. The author inferred from all this 

 that the history of the North Atlantic Ocean might be adduced 

 in support of the views of those who hold the doctrine of the 

 " interchangeability of oceans and continents" rather than of 

 the other. 



Section of Natural Science. — Rev. M. H. Close, M.A., in 

 the chair. — Rev. Dr. Haughton, F.R.S., on the possibility of 

 the formation of coloured solar and lunar halos produced by the 

 suspension in the air of volcanic dust caused by the explosion of 

 Krakatoa in August 1883.— Prof. C. R. C. Tichborne, Ph.D., 

 on an argentiferous galenitic blende found at Ovoca, Co. 

 Wicklow. This mineral is very little known ; it has been called 

 " kilmacooite " locally in Ovoca, and it is generally termed 

 "blue-stone" in the Island of Anglesey, the only two places in 

 the United Kingdom where it is found. An analysis of the 

 mineral made by the author gave the following results : — 



This mineral contains various amounts of pyrites according to 

 the situation of the lode. The specific gravity was 473 — inter- 

 mediate between blende and galena — but it was harder than 

 either of these minerals, and was therefore raised by blasting. 

 The author finds by experiments that this mineral is a mechanical 



1 Equal to about 3 troy ounces per ton, 

 mineral may be said therefore to consist of- 



Sulphide of zinc 



Sulphide of lead 



Sulphide of silver ... 



avoirdupois. The 



37 "63 per cent. 

 29'07 11 



