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his various problems without always recurring to the occurring minerals, such as quartz, calcite, galena, mathematical point of view. Unfortunately, one &c., which may be found in almost all the different word must be said regarding the typography. The districts; but this repetition is not tedious. As an present reviewer has seldom read a book so badly | example, the district of Cornwall and Devon may be corrected for the press. There are two pages of taken, in which the main groups are as follows:corrigenda; but a full statement of all the small cassiterite, minerals associated with cassiterite, copper misprints would with difficulty be contained in four sulphides and sulpho-ferrites, copper-bearing minerals or five pages more. If it is not c for o ore, it is of the gozzans, arsenates and phosphates of the u forn, or l for t, or b for h, or das for dass. This copper-gozzans, ores of lead, zinc, antimony, &c., is the more to be regretted because-granted the sulphides and sulpho-salts, ores of iron, &c., minerals author's point of view the i's of the philosophy are of the rarer metals, the spars of the mineral veins, quite carefully dotted.

miscellaneous minerals.

Apart from a few minor misprints, the only point

which calls for criticism is that undue importance BRITISH MINERALS.

seems to have been attached to many quite trivial and A Handbook to a Collection of the Minerals of the

local names. As for the printing, there is certainly British Islands in the Museum of Practical Geology.

much room for improvement; the lines are so badly By F. W. Rudler, I.S.O. Pp. x+241. (London :

broken that it is surprising that the whole did not H.M. Stationery Office, 1905.) Price is.

fall to pieces in the course of printing.

L. J. S. SINCE his retirement from the post he so long

and efficiently held as curator of the Museum of Practical Geology, Mr Rudler has installed in that

OUR BOOK SHELF. museum a collection illustrative of the modes of occurrence of British minerals. The museum has Moths and Butterflies. By Mary C. Dickerson. long possessed collections of British rocks, fossils, and

Pp. xviii + 344; with 200 photographs from life by

the author. (Boston, U.S.A., and London : Ginn ores, the last named arranged under the various

and Co., n.d.) Price 5s. net. metals which they contain. In the new collection,

This is a prettily got-up book, intended for the which is neatly arranged in twelve table-cases, the

training of classes in “nature-study," with reference minerals found in each district are brought together; /

to a considerable number of common and conspicuous half the space is allotted to Cornwall and Devon, one- North American butterflies and moths, the life-history eighth to Scotland, Ireland, and the Isle of Man, of which is very fully described and illustrated. The and the remainder to the rest of England, the concluding chapter, on collecting, keeping, and divisions being roughly according to the several

studying, recapitulates the points to be noted in

practical observations on the insects themselves. mining districts, with a general group for the

To English readers the book will be useful for the minerals of the Neozoic strata. The specimens, information it supplies about American forms, and to the number of 1652, have mostly been selected from also as indicating a similar method of study for the Ludlam collection, which was bequeathed to the British insects, but many of the species here noticed museum in 1880; though mostly small in size, they

are much larger and more conspicuous than those

likely to fall under our own observation, among them are of excellent quality. In addition to the name and

being several species of Papilio, and large Saturniidæ. locality attached to each specimen, there are many

The figures, of which (including apparatus, &c.) explanatory labels in the cases, and the present there are 233 in all, are generally very good, though volume admirably serves the purpose of a guide to the some are indistinct. The frontispiece, representing collection.

a Smerinthus at rest, and Fig. 17, on p. 147, repreThe volume is by no means a tedious catalogue or

senting a procession of the young caterpillars of

Saturnia, may be specially noticed. But it looks descriptive list of all the individual specimens, but is

odd to see a Smerinthus closely allied to our own rather an extremely readable and interesting account S. ocellatis called “a most beautiful little moth " of the mode of occurrence and history of the more (p. 232); and, though we do not object to the use of common British minerals, especially those which are appropriate English names, we are sorry to see on of economic importance. Instead of long descrip

p. 231 a Sphinx allied to S. convolvuli called “the

Humming-Bird Hawkmoth," a name by which the tions of the characters of species, much is said of

very different Macroglossa stellatarum has been known their paragenetic relations, and many valuable

all the world over, ever since the commencement of suggestions are made as to their possible modes of the study of entomology. origin. The book will therefore be found interesting We had expected to find some notice of the and instructive not only to mineralogists, but also to gipsy moth, the crusade against which has recently geologists and miners; whilst quite apart from the

been given up in America in despair, but find only a

passing reference. I lew British species are noticed, collection, for which it is primarily intended, it will

such as Vanessa antiopa, called in America the have a permanent value as a treatise. In this con

mourning cloak, a translation of its German name; nection mention may be made of the numerous and V. atalanta, Pieris rapae, &c. extremely valuable references to original authorities A great deal of useful general information is given consulted in the preparation of the work.

in the book, and it seems on the whole to be careful The mode of treatment is a novel one, and neces

and accurate. One statement, however true in the sarily involves

abstract, ought not to have been made without quali a certain amount of repetition, | fication or explanation in a popular book. On. p. 265 especially in the case of some of the more commonly | we read, “We are familiar with the fact that all living

creatures develop from eggs." Further comment is addition to a great many data which will be of needless.

special use to astronomers, there will be found a Although published in 1901 and mentioned in the very full list of towns, in alphabetical order, at Zoological Record for that year, this book has not which totality occurs, with the times of the different previously been brought under our notice.

phases of the eclipse. More generally useful

perhaps will be found the maps at the end of the Second Stage Magnetism and Electricity. By Dr. R. volume. These include a map of the world showing Wallace Stewart. Second edition. Re-written and the position of the track from the commencement to enlarged. Pp. viii + 416. (London : W. B. Clive.) | the end of totality over the earth's surface. A second Price 35. 6d.

illustrates on a larger scale the Spanish portion of the Tus book is primarily intended to serve the purposes | track, with special lines showing the times of occurof a candidate preparing for the second stage examina- | rence and duration of totality. The third, on a much tion under the Board of Education (secondary larger scale (1 : 1,000,000), indicates that part of Spain branch). In reading it, we have by no means made alone over which the shadow sweeps, and is very comour first acquaintance with Dr. Stewart, and the plete as regards names of places, railways, &c. Lastly, perusal has left us of our old opinion that, whether re two star charts are added, one showing the position of garded as text-books intended to prepare a student for the eclipsed sun among the stars, and the second a key a particular examination or as a source of culture, the map to this chart giving the designations of the stars books prepared by the author can be very earnestly and planets in this region. recommended. He is a lucid and accurate writer. He Visitors to Spain will do well to supplement their know's where to draw the line so that an elementary literature by securing this volume, and thanks are student shall not be repelled by the complication of a due to the Madrid Observatory for producing so useful subject.

a book so far in advance of the event. The present volume is brought up to date. The importance of the field-that is, the medium surrounding

Naturalistische und religiöse Weltansicht. By Rudolf an electrified conductor or magnet-is insisted on;

Otto. Pp. 296. [Tübingen : J. C. B. Mohr (Paul perhaps even their importance is emphasised too much.

Siebeck), 1904.] Price 3 marks. The tendency of modern thought amongst physicists No better book than this could be recommended to the is to restore to a conductor part, at any rate, of the

young philosophical or theological student who wishes position that it held in pre-Maxwellian days. The di

to obtain a clear and comprehensive view of the deelectric plays a most important part-that is a position,

batable ground where science, philosophy, and won for it by Maxwell, which it can never lose. At

theology meet. The author is well read, a skilful the same time, one should not lose sight of the fact that

debater, a vigorous writer; and as handbooks ought there must be some mechanism at the ends of a line of

not to be unnecessarily multiplied, it is to be hoped induction, and to-day that mechanism is being studied

that this one will be translated. under the name of electron. The electron is an essen

Like many other works in defence of religion in tial part of a conductor, and the complete phenomena

general, the book is not so strong on the constructive of electricity are not fully accounted for without includ

as on the critical side. The author refers with ing it. The volume is almost entirely re-written. It is not

approval to the attitude of Kant when he solved cersurprising, therefore, that there are some unfortunate

tain contradictions or antimonies by a reference to the slips which have escaped the vigilance of the reader.

world of things in themselves. As this is precisely As these are misleading, we will state that on the

the point where Kant's philosophy is most seriously bottom of p. 33“ positive ” and “ negative” should be

questioned, the argument probably suffers to that interchanged. The following phrase (p. 42) is very

extent. But, on the other hand, the author fully misleading :- .“ The portions of those walls, which are,

realises the unity of the various phases of the one as it were, in the shadow of these objects, possess no

problem religion versus naturalism, and the harm induced charge." We think that the first thirty pages

which has been done by concentrating the attention might be improved in any later edition. Consider

on one phase (e.g. the question of miracles) as if it

were the whole. able care has evidently been taken; vet in many cases confusion is introduced by the neglect of some tiny

The work is valuable mainly for its survey of the detail. Thus, in describing the attraction and repul

most interesting biological theories of the last cension of a pithball with subsequent re-attraction, if in

tury, from Darwin, Häckel, Weismann, down to the interval it comes in contact with ar earth-con

Wolff, Korschinsky, Driesch. The philosophical denected body, the phrase that we have put in italics is

velopment of this last writer is sketched in an omitted ; and in several cases where a body is touched

enlightening fashion. With regard to the general to earth it is not explicitly said whether the contact is theory of development and "descent," the author to be broken before a succeeding operation is per

comes to the conclusion that with the confirmation formed or not. Why is it “ evident” (p. 16) that of any such theory only something relatively external doubling a charge will double the force it exerts on

is given, a clue to creation, which does not so much another charge?

solve its problems as group them afresh. The index

at the end of the work gives an explanation of the Memoria sobre el Eclipse Total de Sol del dia 30 de

more difficult terms employed by modern theorists. I gosto de 1905. By D. Antonio Tarazona. Pp. 125. (Madrid : Bailly-Bailliere E. Hijos, 1904.)

An Introduction to Proiective Geometry and its ApTusk who are familiar with the Spanish language

plications. By Dr. Arnold Emch. Pp. vii + 267. and have made up their minds to go abroad and see

(New York: Wiley and Sons; London: Chapman the approaching total eclipse of the sun will find in this

and Hall, Ltd., 1905.) Price 1os. éd. bwk a great amount of useful information relating to This text-book of modern projective geometry forms an this interesting event. The work is issued from the admirable introduction to the subject, and should be Madrid Istronomical Observatory, the director, Fran- known to all who are interested in this branch of risco Iñiguez, having contributed a brief preface, and mathematics. The first chapter deals with the general runtainfull particulars concerning the elements of properties of projective ranges and pencils and their this eclipse ; in fact, it might be considered a treatise products, including harmonic and perspective projecon the subject, so complete is the information. In tion, and the projective properties of the circle. Then

follows an investigation of collineation in a plane, com- | coefficient of friction between the man and the board prising perspective transformations, and the linear exceeds a certain finite quantity. transformations of translation, rotation, and dilata The board rests on a smooth table, but the coefficient tion, with combinations of these. The intimate relation

of friction now depends on both the board and the table, that exists between projective and descriptive geometry

and this may be quite different from that between the is shown. The third chapter gives the general theory

man and the board. There is nothing amiss in supposing

this coefficient to be zero. One way of effecting this of conics, the projective properties of the circle being

experimentally would be to polish the table and remove extended to conics by perspective transformations. The

all roughnesses from it. This was the plan indicated. next chapter deals with pencils and ranges of conics

Where, then, is the inconsistency? and their products, and especially with cubics, the

By using the ordinary abbreviations of language, the latter being classified under the five standard types by wording of the question has been made concise, and thus the help of the Steinerian transformation. Through attention was specially directed to the dynamical principle out the book analytical and geometrical methods are involved in the solution. employed side by side, some portions of the subject The problem has been understood by so many students being better suited to the former treatment; moreover,

in the sense above described, and worked without a single the analysis affords excellent illustrations of modern

objection having been raised, that I think the meaning analytical geometry. The main purpose of the author

must be perfectly clear. Indeed, I cannot imagine what other meaning it could have.

E. J. RouTH. has been to develop the subject in regard to its prac

May 20. tical applications in mechanics, and the last chapter is devoted to such examples. Thus we find problems in

On the Spontaneous Action of Radio.active Bodies graphic statics, plane stresses, and in the stress ellipse

on Gelatin Media. of an elastic material, and there is an interesting account of various linkages by means of which linear and

In the course of some experiments on the formation of perspective transformations can be mechanically ob

unstable molecular aggregates, notably in phosphorescent tained. The book is excellently got up in every way,

bodies, I was led to try whether such dynamically unstable

groupings could be produced by the action of radium upon and the diagrams are quite perfect and may well serve

certain organic substances. It will scarcely be necessary as models of what such figures ought to be. The author

to enter here into an account of the many speculative exis a very clever draughtsman, and his skill as a writer periments which I have at one time or another tried, but is equally pronounced.

it will suffice if I describe, as briefly as possible, the experiment which, amongst others, has led to a very curious

result, and that is the effect of radium chloride and LETTERS TO THE EDITOR.

radium bromide upon gelatin media, such as those

generally used for bacterial cultures. [The Editor does not hold himself responsible for opinions An extract of meat of 1 lb. of beef to i litre of water,

expressed by his correspondents. Neither can he undertake together with i per cent. of Witter peptone, i per cent. to return, or to correspond with the writers of, rejected

of sodium chloride, and 10 per cent. of gold labelled manuscripts intended for this or any other part of NATURE. gelatin, was slowly heated in the usual way, sterilised, No notice is taken of anonymous communications.)

and then cooled. The gelatin culture medium thus pre

pared, and commonly known as bouillon, is acted upon by Fictitious Problems in Mathematics.

radium salts and some other slightly radio-active bodies in

a most remarkable manner In my younger days it was well recognised that such

In one experiment the salt was placed in a small statements as “ perfectly smooth” and the like were

hermetically sealed tube, one end of which was drawn out mere conventional phrases for designating an ideal state

to a of matter, which was assumed to exist for the purpose

fine point, so that it could be easily broken.

This was inserted in a test-tube containing the gelatin of simplifying the mathematical conditions as far as

medium. The latter was stopped up with cotton wool in possible. Nobody can learn mathematics without working

the usual way with such experiments, and then sterilised out a large number of problems and examples, and in

at a temperature of about 130° C. under pressure for about order to make these sufficiently easy for the beginner,

thirty minutes. Controls without radium were also at various fictitious hypotheses have to be introduced. Similar objections would apply to the phrase " friction

various times thus similarly sterilised. less liquid ” ; but it would be impossible for anyone to

When the gelatin had stood for some time and become

settled, the fine end of the tube containing the radium salt learn hydrodynamics without first studying the mathe

was broken, from outside, without opening the test-tube, matical theory of this fictitious form of matter. In fact,

t; by means of a wire hook in a side tube. the introduction of viscosity leads to such formidable

The salt, which in this particular experiment consisted difficulties, that nobody has yet succeeded in solving such !

of 2 milligrams of radium bromide, was thus allowed to a simple problem as the motion due to a doublet situated

drop upon the surface of the gelatin. at the centre of a sphere; and the solution, if it could Afte

After twenty-four hours or so in the case of the be obtained, would throw much light on the mode of

bromide, and about three or four days in that of the attacking more difficult problems.

A. B. Basset.

chloride, a peculiar culture-like growth appeared on the May 28.

surface, and gradually made its way downwards, until

after a fortnight, in some cases, it had grown fully a IN NATURE of May 18 the wording of a problem set

centimetre beneath the surface.

If the medium was sterilised several times before the near the beginning of my “ Rigid Dynamics” is rather adversely commented on. In the problem

radium was dropped on it, so that its colour was altered, a man is de

probably by the inversion of the sugar, the growth was scribed as walking along a perfectly rough board which rests on a smooth table, and the criticism is that the two

greatly retarded, and was confined chiefly to the surface. suppositions are inconsistent; but this depends on what

It was found that plane polarised light, when transmitted is meant by the words used, and perhaps I may be allowed

through the tube at right angles to its axis, was rotated to make an explanation.

left-handedly in that part of the gelatin containing the

growth, and in that part alone. When bodies are said to be perfectly rough, it is usually

The controls showed no contamination whatever, and meant that they are so rough that the amount of friction

no rotation. The test-tubes were opened and microscopic necessary to prevent sliding in the given circumstances

slides examined under a twelfth power. They presented can certainly be called into play. In art. 156 of the treatise on dynamics, just after the laws of friction have

the appearance shown in Fig. 1. At first sight these been discussed, the words “ perfectly rough” are defined

seemed to be microbes, but as they did not give subto have this meaning. The board in question has there.

cultures when inoculated in fresh media they could

scarcely be bacteria. The progress of any of the subTore no special peculiarity. All that is stated is that the cultures after a month was extremely small, and certainly

too small for a bacterial growth. It was not at all obvious | from the physicist's point of view, is that of long and, so how bacteria could have remained in one set of tubes and far as possible, continual observation, a method similar not in the other, unless the radium salt itself acted as a to that which the astronomer is bound to adopt in his shield, so to speak, for any spores which may originally study of bodies over which he has not the control to deal have become mixed with the salt, perhaps during its manu with as he pleases. facture, and when embedded in it could resist even the From the accompanying photographs it will be observed severe process of sterilisation to which it was submitted. that they are not all of the same size; they range from

On heating the culture and re-sterilising the medium, the about 0:3 u to the minutest specks; they are mostly, if bacterial-like forms completely disappeared; but only not altogether, all of the same shape, and show distinct temporarily, for after some days they were again visible signs of growth; the larger ones appear to have sprung when examined in a microscopic slide. Nay, more, from smaller forms, and these in turn from still smaller they disappeared in the slides when these were ex ones, and they have all probably arisen in some way from posed to diffused daylight for some hours, but re the invisible particles of radium. appeared again after a few days when kept in the dark. Fig. 2 distinctly shows the existence of nuclei in the Thus it seems quite conclusive that whatever they may | larger and more highly developed forms, whilst Fig. 3 be, their presence is at any rate due to the spontaneous reveals, though indistinctly, what is their most remarkable action of the radium salt upon the culture medium, and property of all, and that is their subdivision when a certain not alone to the influence of anything which previously size is reached. They do not grow beyond this size, but existed therein.

subdivide. When washed they are found to be soluble in warm These photographs, together with the numerous results water, and however much they may resemble microbes, of eye observations, which indicate that a continuous

growth and development take place, followed by segregation, leave little doubt that whilst on the one hand they cannot be said to be bacteria, they cannot be regarded as crystals either in the sense of being merely aggregates of symmetrically arranged groups of molecules, which crystals are supposed to be. The stoppage of growth at a particular stage of development is a clear indication of a continuous adjustment of internal to external relations, and thus suggests vitality

They are clearly something more than mere aggregates in so far as they are not merely capable of growth, but also of subdivision, possibly of reproduction, and certainly of decay.

The subcultures do show, however slightly, some indicacation of growth after four or five weeks, although that growth is, I understand, too small for a bacterial sub

culture. Moreover, when examined in the polariscope they Fig. 1.

FIG. 2.

have not been found to yield the characteristic figures and changes of colour which crystals generally give.

Thus for these reasons I have been led to regard them as colloidal rather than as crystalline bodies, and probably more of the nature of “dynamical aggregates " than of " static aggregates," of which crystals are composed.

There appears to be a tendency amongst text-book writers to classify minute bodies which are not bacteria as crystals, but really without sufficient reason, and as these bodies cannot be identified with microbes, on the one hand, nor with crystals on the other, I have ventured, for convenience, in order to distinguish them from either of these, to give them a new name, Radiobes, which might, on the whole, be more appropriate as indicating their resemblance to microbes, as well as their distinct nature

and origin. FIG. 3.

Some slightly radio-active bodies appear also to produce

these effects after many weeks. thry cannot for this reason be identified with them, as A more detailed account of these experiments will be also for the fact that they do not give subcultures as published shortly. This note merely contains some of the bacteria should.

principal points so far observed. Prof. Sims Woodhead has very kindly opened some of I have to thank Mr. W. Mitchell, who sterilised the the test-tubes and examined them from the bacteriological tubes, for the assistance he has rendered in these experipoint of view. His observations fully confirm my own. ments.

JOHN BUTLER BURKE. He assures me that they are not bacteria, and suggests Cavendish Laboratory, Cambridge, May 10. that they might possibly be crystals. They are, at any rate, not contaminations. I have tried to identify them with many crystalline

The Consolidation of the Earth. bodies, and the nearest approximation to this form appears to be that of the crystals of calcium carbonate, but these There are several points in Dr. See's last letter (NATURE, are many times larger, and, in fact, of a different order of | May 11) calling for remark from the geological point of magnitude altogether, being visible under comparatively view. low powers; and are, moreover, insoluble in water.

(1) The effect of (hydrostatic) pressure at depths tends A careful and prolonged examination of their structure, not to liquefaction (as in the case of the ice of a glacier) behaviour, and development leaves little doubt in my mind but to promote crystallisation, the condition of the greatest that they are highly organised bodies, although not density of mineral matter, as I showed years ago in my barteria.

little work on metamorphism in discussing the relation of l'nfortunately the quantity is so very minute that a the crystalline to the vitreous states. It is here that the Chemical analysis of their composition is extremely difficult. importance of “solid-liquid critical state" comes in. The amount of salt in the first instance is so small, and (2) We have no right to assume the existence at any the number of aggregates, or whatever they may be, thus stage of the history of our planet of a mere molten ball produced perhaps still smaller.

radiating heat directly into cold space, since in that The most effective method of studying their properties,“ pre-oceanic stage " it was surrounded by a non-conduct

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[graphic]
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ing mantle or jacket” of such enormous density and the dynamical residual vertical obtained by subtracting the altitude as to contain (as its main constituents) (a) the acceleration of the instrument (as a vector) from that of greater part of the water of the present hydrosphere in gravity. (I disregard, in this statement, the slight lag the vapour state; (b) the CO, locked up in the lime due to viscosity.) stones and other carbonates of the lithosphere, as well as A couple of simple experiments, serving to emphasise that represented by the coal and the living vegetation of this, may be suggested. A spirit-level is suspended in a the globe ; (c) the hydrocarbons possibly represented by horizontal position by two equal strings attached one to Archæan graphite, together with (d) the halogens (if cach end. In one case the strings hang vertically from atomic evolution had reached that stage), including the two hooks; in the other case they are attached both to Cl, of the 73 per cent. of the NaCl of the salts of the one hook. If the level is set swinging in the plane of the present ocean. It is conceivable that a vast convection strings, then in the first case the bubble will be found to system existed, as the outer zones of the primordial atino have an oscillatory inovellent relatively to the tube, the sphere underwent cooling with consequent condensation, tube having linear acceleration but no tilting movement. and descended towards the molten globe; but there could In the second case the tube has both movements, but their scarcely be contact generally between such cooler portions effects exactly neutralise each other, and the bubble reand the heated molten mass. The conditions would be

mains stationary in the tube. The expert waiter (may it rather such as are partly illustrated by what a student of be added ?) who hurries about with plates of soup has a physics is familiar with as the “ spheroidal state” of a very effective empirical knowledge of this last case of liquid floating on a cushion of steam above a hot plate of compensation. metal. Under the enormous pressure prevailing at the

The motion of the bubble of a level has been brought surface of the globe in that pre-oceanic stage of its history forward as evidence in favour of the undulatory character great quantities of superheated steam and other gases of the disturbance producing the motion ; but if the above must have been mechanically included, and in some cases, suggestions are to be accepted, the motion might as reasonperhaps, occluded, in the hot crust in the inceptive stages ably be urged as evidence of a horizontal disturbance; the of its development by congelation; and in such circum truth being that the instrument is sensitive to both disstances, as I suggested seventeen years ago, superheated turbances, and is quite ineffective as a means of diswater in traces would probably enter into the composition | criminating between them. of such silicates as hornblende and mica, the two most

The evidence referred to is contained in the British characteristic of the minerals of the heavier metals of the Association report, 1902 (seismological committee report, Archæan gneisses and schists. A vear or two later that p. 72). The view finds acceptance in some recent and hypothesis received demonstration from the splendid work of i authoritative works, and seems, So far, to have passed de Kroustchoff (see Nature, vol. xliii. p. 545. also Bulletin | unchallenged.

G. T. BENNETT. de l'Académie des Sciences de St. Petersbourg. tome xiii.. | Emmanuel College, Cambridge. “ Über künstliche Hornblende,” by K. von Chrustschoff). So, I take it, we can understand how such a crust could float on a magma of molten rock material, just as air

A Feather-like Form of Frost. charged fragments of pumice or of charcoal float on water, The accompanying photograph shows a form of frost yet sink quickly to the bottom under the exhausted re- not, I believe, usually seen except at a comparatively high ceiver of an air-pump; or as even a coil of platinum foil altitude and unsheltered position. This photograph was (sp. gr. 21.5) can be made to float in water inside a good air pump, as it is pontooned by innumerable bubbles of distended atmospheric gases previously condensed upon its surface; or, again, as masses of lava slag of large dimensions are seen to float for a time upon the vast lake of liquid rock material in the crater of Kilauea. With tidal action in the magma greater when the moon was nearer the earth than at present, such a thin crust would easily undergo disruption, while portions of it would float off and be engulfed in the magma. This view, which I propounded some seventeen years ago, had been anticipated partly by Zöllner, and was adopted by the distinguished American geologist, Dr. A. C. Lawson, to explain the phenomena presented by the enormous inclusions of more basic rock masses in the gneiss of the Rainy Lake region, which excited great interest among our leading British geologists at the International Geological Congress in London in 1888, though it seems at the time to have been very imperfectly perceived by most of them. So far the evidence we have goes to support Dr. See's contention that the descent of such masses into the magma would be arrested long before they even approached the centre of the sphere: but one feels great difficulty in following his argument based on Laplace's law,” for reasons given in my former letter (NATURE, May 4).

Fig. 1.- Frost“ feathers" on windward side of rock.
By a slip I wrote, it appears, “ impossibility” for possi-
bility in the top line of p. 8 in my last letter.
Bishop's Stortford, May 17.

A. IRVING.

taken on April 22 near the summit of Carnedd Llewelyn, N. Wales (3484 feet above sea-level). These delicate frost feathers” appear gradually to grow outwards from the

rock face on the windward side, and the delicacy of their The Spirit-level as a Seismoscope.

form is, no doubt, modified in some degree with the vary.

ing rate of the wind and the temperature. I have found, A MISCONCEPTION seems to prevail among seismologists in the same district, these “ feathers " 9 inches from root as to the behaviour of a spirit-level. A displacement of to tip; those shown are about 6 inches long. They form the bubble is regarded as conclusive evidence of the tilting ; a comparatively solid mass where they touch, but the tips of the instrument. It should be pointed out, however, keep distinct, and the whole mass is in reality very brittle, that this is far from being the case. For a second cause and easily breaks up into small pieces. equally effective in producing displacement of the bubble,

H. M. WARNER. is a horizontal acceleration of the instrument in the direct 44 Highbury Park, N., May 16. tion of the tube. The position of the bubble should be Dutt n, “Earthquakes in the Light of the New Seismology," p. 137 : taken as indicating, not the normal statical vertical, but | Davison, "A Study of Recent Earthquakes," p. 280.

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