so6 NATURE (SEPTEMBER 22, t904

Is Selenium Radio-active? THE HEART OF SKYE.' lT occurred to me recently that a possible ·method of deciding between the two hypotheses which have been THIS volume of detailed -description, raising brought forward to explain radio-activity, namely, that of in its successive chapters questions of profound atomic degradation (Rutherford and Soddy, Ramsay, &c.) interest in philosophic , proves that the Geo• and that of molecular change (Armstrong and Lowry, Proc. logical Survey of the United Kingdom is confident Roy. Soc., 1903), lay in attempting to realise radio-activity that the scientific spirit should permeate its public in the case of an element well known to undergo molecular work. None of the rocks dealt with possesses at pre• change readily, but with an atomic weight small enough sent an economic value; most of the area is untraversed to exclude the probability of an atomic instability such as by roads, and the exposures are not to be sought in is assumed for radium and thorium. Such an element is quarries, but in rain-swept uplands, or high on selenium (at. wt. .79), which suggested itself to me as a desolate mountain-walls. Yet no detail is regarded suitable material to experiment with because, under the as unimportant; the surveyor, for months together, influence of light, it undergoes a remarkable alteration in its electrical resistance and E.M.F. of contact, suggesting leads a life as hard and remote as that of an Alaskatt an allotropic change of an altogether unusual character. pioneer; and the result is a book in which the daily As this change, whatever be its real nature, occurs almost difficulties are concealed, while an array of facts is instantaneously (Bellati and Romanese, A tti R. I st. Veneto, given to us, any one of which may help observation 1881 ; Maiorana, Atti dei Lincei, 1894 and 1896), it seemed in other and more favoured lands. possible that the rapidity of the intermolecular vibration Few lands, however, are more favoured in scenery, might be sufficient to cause a radiation similar to that of and the defects of Skye are mainly meteorological. radium and thorium which, by " ionising " the selenium, The very audacity with which the black Cuillins rise would render it conducting. In order to ascertain whether from the edge of the Atlantic seems a temptation to such a hypothetical radiation could be detected photo• the summer-storms. Yet the glaciated surfaces allow graphically, I exposed a piece of selenium, placed on a of small decay, and Mr. Harker directs our attention photographic plate, wrapped in three thicknesses of black to the remarkable freshness of the rocks. Despite the glazed paper, during thirty-six hours to the bright sunshine of July. On developing the plate a distinct black stain on absence of maps, the crystalline core of the island, with a background of clear glass indicated the position the its striking scenic contrasts, long ago attracted selenium had occupied. The first experiment was made geologists, and has been again described, in all its with. ordinary vitreous selenium, and the stain, although picturesqueness, by Sir Archibald Geikie in our own distinct, was not very . pronounced. A second experiment day. \Ve well remember the seductive map, on the with freshly prepared " metallic" selenium, obtained by scale of four miles to an inch, with which we ourselves heating the vitreous variety at 190° for half an hour and tramped across the boggy grasslands, or wandered then cooling very gradually to the ordinary temperature, midnight prodigality above the Sound of Sleat; and gave a much mote intense stain on the negative. Mr. Harker complains that, even now, names and I should have hesitated before publishing these experi• details are not always exactly placed on the sheets ments il1' their present form had I not,. since. they were issued by the Ordnance Survey. The work that he has made, seen a paper in the Physikalische Zeitschrift of now done, and the manner of it, will be honoured by August 25 in which similar results are recorded by J. J. Taudii;J Chabot. This observer, approaching the sub• all who know the island. ject from a different direction, has also been led to the The view that the crystalline central masses repre• conclusion that selenium in a selenium " cell " is feebly sent the core of the volcano from which the abundant radio-active to the extent of emitting radiations capable of plateau-basalts flowed appears to be now untenable, passing through black paper and affecting a photographic although some kind of a volcano, and a fairly large plate. It may, of cburse, be urged that the stain on the one, may have existed on the crown of the great lacco• plate is due to selenium vapour penetrating the paper in litic dome. Certain earlier volcanic vents, moreover, which the plate is enclosed. I am therefore making experi• provide curious evidence that gabbro and granite ments in which this possibility is excluded. Further, --I existed, in a consolidated form, down below, while intend studying the beha.viour of sulphur, as it is already the plateau-basalts were being extruded. In a very known that the other members of the selenium family, remarkable passage (p. 24), the author shows that namely, oxygen and tellurium, can in certain circumstances give rise to radio-active phenomena. W. A. DAVIS. even the sequence of these rocks was the same as that City and Guilds of London Institute, Central now known to exist in the central laccolitic area. The Technical College, S. W. acid tuffs of Skye containing granite (p. zo), the basic tuffs crowded with fragments of gabbro (p. 2 r ), go far as evidence of the continuity of lava-types with Rare Moths in England. holocrystalline representatives below. It is interesting MRs. THOMAs's letter in your issue of September 8 is to remember that, when Prof. Judd wrote his well interesting, both as affording definite proof that Deilephila known papers, this natural-history view of igneous livomica does sometimes breed in this country, and as rather masses was very far from general acceptance ; and tending to support the view that this species enters the the fact that he strove for it so successfully has been country from abroad-for the proximity of Warmwell to the sea is certainly suggestive. obscured by the subsequent controversy as to the local Apropos to rare moths, it may be of interest to state that sequence in. the Hebrides. I recently took a specimen of Deiopeia pulchella on the cliff Mr. Harker, in dealing with the basalt plateaux here. This moth used to be so rare that Newman wrote:• (pp. 29, 239, and 435), shows excellently how large a " Mr. Doubleday has a single specimen taken at Epping, part is played by the abundant intrusive sills. These and we believe there are two or three other British speci• form, indeed, on weathering, most of the terraced mens in different cabinets." Since that was written the structure that observers were formerly apt to attribute number of English specimens has, of course, been increased, to successive lava-flows. It is remarkable (p. 12) that but I believe that the insect is still considered a rarity; and the dykes or vents can so rarely be traced into the the scarce occurrence of a weak-flying moth like this, which lava-sheets to which they gave rise; but this is a one can hardly suppose could cross the Channel, and which common <:omplaint in all areas of copious and long• has been found so far inland as at Epping, is a greater continued activity. The temporary theory of fissure- puzzle than the rarity, but occasional comparative abundance, of a strong-flying hawk moth. I "The :rertiary Igneous Rocks of Skye." By , M.A., F. H. PERRYCOSTE. F.R.S., wah by C. T. Clough, M.A., F.G.S. Pp. xii + 482. Higher Shute Cottage, Polperro, (Memoirs of the Geological Survey of the United Kingdom. Glasgow: R.S.O. Cornwall, Printed for His Majesty's Stationery Office by James Hedderwick and September 12. Sons, 1904.) Price gs. NO. 1821, VOL. 70] © 1904 Nature Publishing Group SEPTEMBER 22, 1904] NATURE

eruptions has been practically modified into that of suggests rapidity of solution. But the case is eruption from a large number of small and easily con• certainly a n uncommon one,. as other contacts of these cealed vents, which were doubtless situated along two rocks show. Down below us as we write, an fissures ; and this theory is borne out by observed ancient granite sends off zig-zag veins abundantly into occurrences along rifts on Etna. Mr. Harker himself the " " limestone of Donegal; behind us, points out (p. 14) that " the great thickness and extent the same granite produces a coarse quartz-diorite, by of the basalt group results only from the superposition interaction with a basic sill of the same series. A and overlapping of a vast number of separate flows, little south, at Summy Lough, the pre-Devonian each of which is of very insignificant dimensions." gabbros have brought up inclusions of an earlier The small group of trachytes a nd rhyolites (p. 56) gabbro, which " weather into little hollows," like those in Skye occurs clearly between two series of basalts, of the corrie of Tairneilear. In the universality of the a fact very satisfactory for Irish geologists, who have problems discussed by Mr. Harker lies their wide had to maintain similar views for their acid lavas on g eological attraction; and we venture to think that less convincing evidence. Much of the interest of many of his questions will receive their answer in more the petrographic details furnished by Mr. Harker lies distinctively plutonic regions. For a long time, Con• in the attack of one rock on another. The dissection tinental geologists maintained that some fundamental of an early peridotite by an overpowering mass of difference separated our modern lava s from the crystal• gabbro (p. 64), the occurrence of " xenoliths " of one line masses revealed in older regions of the crust. kind of gabbro in another (p. rzr), the mutual modifi• Similarly, our fluidal gneisses, with their mutual inter• cations of gabbro and granite in the Red Hills (p. r83), actions, have been held to be something primordial which are justly attributed to a process of diffusion, and apart. This purely mental barrier is now rapidly may be named as examples of the important problems breaking down, and we may find that the phenomena dealt with. We confess to a personal interest in the so carefully set before us in the case of Skye have results of Mr. Harker's researches on composite sills (p. 209), where an acid rock is shown to pick up fragments of an earlier basic one, and to discharge, as it were, its own porphyritic crystals into the latter along its margins. Such facts make us doubtful of the necessity for assuming a distinction between " segregation-veins," with ill-detlned edges, and " ordinary veins of intrusion " (p. 78), or for the belief that bands, the crysta ls of which interlock at the common surface, " must have existed side by side in the fluid state " (p. I 19). The discussion of the banded gabbros, with the beautiful plates accompanying it, forms a chapter of exceptional value, though it hardly does justice to Mr. Harker's own recent work, in which he has explained the genesis of a Cain• ozoic banded gneiss. The refer• ence (p. ns) of the " pyroxene• granulites " of Skye to " altered FIG. r.-View of Sgurr nan Gillean. (From" The Tertiary Igneous Rocks of Skye." representatives of basic lavas en• tangled in the gabbro complex " is in happy agree• deep-seated and more impressive representatives in the ment with the most modern views as to similar rock• floor of Saxony or Norway. masses in the Saxon metamorphic a rea. Mr. Harker's book, with its handsome photographic A local rock of hybrid origin is termed marscoite illustrations, is published at a very moderate price, (pp. 175 and 192); this occurs as sills, and is regarded seeinP" tha t it appeals entirely to the professed geologist. as a basic magma modified by the absorption of Indeed, when dealing with so superb an area, we think granitic material prior to its intrusion. Mr. Harker that a little more descriptive power might have been holds that such " hybrid rocks are essentially abnormal used to unite the scenic and the petrographic features. in composition "; yet it may be urged that in the W e thus wish that chapter xxvi., on " physical features deeper plutonic regions many rock s, which we have and scenery," had sent off intrusive sheets into those come to consider normal, have arisen by processes of that went before it, and had even wrapped round much admixture and diffusion. The junction of the granite of their contents as literarv " xenoliths." \Vith the and the Cambrian limestone in Skye (p. 135) presents ma nner of the text we have little fault to find. It is evidence of solution of the limestone, without addition always clear and direct-far clearer, in fact, than the of lime to the granitic magma. We prefer to believe explanatory diagram on p. 433· The Americans have that a slow diffusion and transference of the lime given us many worse names than " mugearite "; and occurred into the great subterranean m ass, or that the other a uthors beside Mr. Harker have written " amyg• locally modified granitic magma flowed on elsewhere, dule" in pl ace of the obvious "amygdale." "Pheno• leaving new and unmodified materia l in contact with cryst," like " cab " and " bus," must probably be the limestone, rather than to conclude that a rock accepted as a compromise, though we expect better which absorbed gabbro and Torridon Sandstone be• things of scientific men; and the inconect use of haved in a mysteriously different manner towards " granophyre," introduced by Rosen busch , has become dolomitic limestone. The singular absence of veicns widely tolerated through repeated publication. The passing from the granite into the limestone rather t P- ml "ophitic plat?s, •· rather than "ophi tic NO. I82I, VOL. 70l © 1904 Nature Publishing Group 508 NATURE [SEPTEMBER 22, 1904 or "ophitic nodules," where augite or hornblende are notable works appeared, and some of these were concerned, has been sanctioned by microscopists, but , trea tises on medicine. Among others published by tends to mislead when actual rock-specimens are Cockayne nea rly fifty years ago were " The Leech• examined. Beyond these trifling criticisms, we have Book " of Bald (written when Alfred wa s king, or nothing but praise for this conscientious exposition of soon after his death), a book of recipes and a glossary results, behind which lies a vista of per sonal sacrifice of the names of plants, of which the manuscript is and prolonged observation in the field. preserved in the library of the Cathedral of Durham. GRENVILLE A. J. CoLE. The following remarks by Dr. Payne deserve to be widely read, for their application is general :- " Before speaking in detail of the old English ENGLIS H JIEDICINE IN THE ANGLO-SAXON medical books, I will venture to say a word about the TIMES. 1 spirit in which they should be studied. Too often, those few persons who have interested themselves in FROM an educational point of view, an acquaintance these monuments of ancient science have treated them with the hist