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The bawik in mexi-led upon the “ Fodder-grasses of and an unusually large number of examples will be found
India," pubbshed not long ago, in two volumes, by Mr. at the end of each chapter.
Duthie, the d rector of the botanical departmen: ni The work is based on a series of lectures delivered by

orthern India, and to Mr. Duthie she author is indebteri the author at the Firth College, Sheffield, and many
for the botanır al determination of the species. He gives details for which time can generally be found at the
the ratire name of each plant, and a short account of lecture table have in this case found their way into the
the extent and manner in which it is used, and as most book.
of them have a wide dispersion, this will be found These will belp to lessen the individual difficulties ar
veful in other dry sub-tropical regions. Out of thiny, students, and their views of the subject will be enlarged
seven species, the two great tropical tribes are represented thereby. There can be little doubí that the text-book
l'anirea by twelve specife, and Andropogonea by ten, and I will have a deservedly favourable reception.
only three species fall under Festucce, the tribe to which

G. A B most of our North European pasture grasses belong. The plates are lithographed from photographs, and do not Catalogue of the Fossil Reptilia and Amphibia in : contain any dissections. Platelii, called Panicum British Museum (Natural History). Part III., CO(rusgallı, is clearly not that species, but a form of P. taining the Order Chelonia. By Richard Lydekker, colonum, another variety of which is figured on Plate II. BA, F.G.S., &c. (London: Printed by Order of the Mr. ('oldstream also has got entirely wrong with his Trustees, 1889.) tuo species of Cyperus, figured on p. 38. The left-hand

MR. LYDEKKER is to be congratulated on having added figure, called (Cyperus species, is evidently Cyperus Iria, one more to the valuable series of catalogues of the Linn., a common wee i' throughout India in rice-fields. palæontological collections in the British Museum which The left-hand figure, labelled Cyperus Tria, is not in he has compiled during the last few years. Like his flower. There is no such plant known to botany ; Tria previous catalogues, the present work indicates an erroris doubtless a mistake for lvia. The figure is quite mous amount of careful and accurate work, which, hos unrecognizable, but from the native name appended, ever, is of such a special kind that it cannot easily be "Motha," it is most likely (Cyperus rotundus.

summarized in a short review, J. G. B.

The extreme difficulty of correlating the fossil forms Elementary Dynamics of Particles and Solids. By W. M.

of Chelonia with the recent, on account of the frag: Hicks, M.A., F.R.S. (London: Macmillan and Co., by the fact that, out of the 52 genera and 131 species

mentary character of many of the remains, is indicatel 1890.)

or varieties described, the author has only been able to In this excellent treatise, extending over nearly 400 pages, place with certainty 18 genera and 10 species amongs the author introduces to the student the principles of existing forms. The classification adopted is to a great lynamics. Although the book is issued under the latter extent that followed by Mr. Boulenger in his catalogue title, it will be found to differ considerably in its treat- of recent Chelonians. The work is illustrated by : ment from the majority of text-books on the same subject. woodcuts, and abundant references to the bibliography For instance, the two subjects of statics and kinetics have of the group are given. It must be added, as stated in been considered together, the former being regarded as a the preface, that the collection which forms the subject special case of the latter. Again, the discussion of force of this Catalogue is particularly rich in Chelonians from is reserved until an attempt has been made to give an the Purbeck Beds

of Swanage, the Cretaceous of Englani idea of mass and its measurement; thus a preliminary and Holland, the Eocene Tertiaries of Warwick, Shepper, study of momentum finds an early place.

Hampshire, the Isle of Wight, and the older Pliocene of Although the mathematical acquirements of the stu- the Siwaliks of India.” The last-named beds have yielded dent of these pages may be limited to a knowledge of the the largest tortoise known (Testudo [Colossa kelya) elements of algebra and geometry, he will be able to of Falconer), the carapace of which measures about six readily follow the methods adopted in establishing the feet in length. various results. This the author has kept in view throughout his work, except in a few cases where, in the hope of rendering it useful to a larger circle of readers, he has had recourse to the trigonometrical ratios for examples

LETTERS TO THE EDITOR. which he has worked out.

The volume is divided into three portions (1) recti- (The Editor does not hold kimself responsible for optimierz linear motion of a particle ; (2) forces in one plane ;

pressed by his correspondents Natker car ke sederten

to return, or to correspond tot the writers of, WA: (plane motion of a rigid body:

manuscripts intended for täis or any other partNaTuri One cannot read the first few chapters without observing

No notice is taken of anonymous communications.] the care taken by the writer in trying to impart to the student a correct and precise idea of the fundamental

Systems of " Russian Transliteration.** units. That this is a very important matter all will agree As one who takes an interest in the Russian tongue, quite a*** who have had any experience in teaching or testing from the value of the scientific papers pabished in tha: language students. The most deplorable state of ignorance some I may perhaps he allowed to express my regres that the natu times exhibited by them, in giving their results in all of "A t'niform System of Russian Transliteratium, persze manner of absurd units, should encourage both teacher in your issue of February 27 (p. 397. bas departed in an and author to make a special effort when dealing with the every point where it is possible to do so from the system question of units, fundamental or otherwise.

trarsliteration which has been in use in England for abs As the subject of staties is included an opportunity has century, and which has moreover, the advantage or beg ald been taken of introducing the method of drawing stress

identical with that current in France diagrams for loaded framework; this will be valuabie to bases namey, the mania, indi&o * 2000

system of translitera na may be coded me one of je engineering students.

orwithstard ng that the writer has forbicien himself na: in the latter the letters of the treaga lugaz the use of the integral calculus he has been able to where russeble, represented tog etters anys of letters were establish in same cases very neatls many useful results have as beariy as may be the same seeds the orig. For in the no chapers on centre of gravy ard moment of a canze, 5 in Russian acte

represexed by 5 Engs, inertid lich should be read w care.

these staring the sese sonst 1 sease me bat bearr learness in method characteres the book throughout is the most curvenient systez, and see what he

generally adopted; the author of this new “uniform system,” As regards Mr. Kirby's suggestion, the transliteration of the bewever, has chosen the other course.

semi-vowels was discussed, but it was not thought advisable to If the author of the “uniform system" had been contented exaggerate their importance by using two letters for them, wak tabulating the system of transliteration which has been so especially as their use is becoming discontinued in Russia. Long in use, he would have earned the gratitude of those devoted When recommending a uniform system, we did not imagine ko literature, as well as of those who cultivate science. As it is, that Mr. Groves or anyone else would infer that this was I am afraid he has merely given the world of art and letters an intended to limit the right of Russians who diell in England opportunity for gibes at what they are sometimes pleased to call or who write in English to spell their names as they please ; the narrow mindedness and pedantry of scientific men.

we have not asked Messrs. Kelly to apply it to all Russian I may, perhaps, be permitted to give a few examples of the names in the Post Office Directory or the Court Guide ; we Jefects of the new system ; r in Russian has three sounds, one should never think of altering such names in ordinary corre. nearly resembling the English g, another very like h, and a third spondence. Even catalogues and records, for which this puttural sound, to which there is nothing analogous in our system is intended, the familiar form should of course be quoted tongue. The author proposes to get over this by transliterating with a cross reference, as recommended by us in the clause r Ivy gh!!. The eminent chemist Hemilian thus becomes dealing with proper names, masked as Ghemilian, whilst Gustavson appears as Ghustavson, Mr. Groves asks why we have not tabulated “the system which and a well-known political character, Gortchakoff, is altered to has been in use in England for about a century." Our efforts began Ghorchakov. For comparison, I give these names, and a few with an attempt to discover such a system, and resulted in the Chers, as transliterated in accordance with the two systems : tabulation of a large number of systems, including that employed

by Mr. Groves in the Journal of the Chemical Society; since, Present system,

New system.

however, no two authors agree in the English symbols intended Hemilian

Ghemilian.

to represent, either the sounds or letters of Russian words, we Gustavson

Ghustavson'.

endeavoured to frame a system combining as far as possible the Gortchakoff

Ghorchakov'.

features of those already in use in England and America. Alexéeff

Aleksyeer'.

We are much obliged to Mr. Groves for supplying further Gregoreff

Ghrighor'ev'.

illustrations of the desirability of using gh for r; the letter has, Ogloblin

Oghloblin.

of course, more than the three sounds to which he limits it. Mendeléeft

Mendelyeev.

The uniformity of "the system which has been so long in Chroushtchoff ...

Khrushchov,

use " may be illustrated by the following examples, in which we Michael

Mikhail.

confine ourselves to the names of chemists, and to the words Joukovsky

Zhukovskič.

quoted by Mr. Groves :Geographical names are even more weird; for example, it teer,” and Keith Johnston's " Atlas” alone, we find Nijni, Nijnei,

Consulting the "Imperial Gazetteer,” Lippincott's “Gazeti recomes somewhat difficult to recognize under the disguise of Nishnii, Nizhnee, Nijnii, and Nischnii-Novgorod. Vizhni Novghorod and Volgha, the town of Nijni Novgorod and the River Volga. Such words as “Journal" and "Chemie,"

One journal is given in Bolton's “Catalogue of Chemical

Journals” as when occurring in titles, can be at once recognized ; this can marcely be said of them if the new system of transliteration is Zhurnal russkova khimicheskova i fizicheskova ; usat, as they become "zhurnal” and “Khimis" respectively. It is much to be regretted that the Royal Society, the Linnean

in the Geological Record as Society, and the Geological Society should have pledged them

Jurnal rosskoi chimitcheskago i phizitcheskago ; selves to adopt this novel " system of transliteration," instead and in Scudder's “Catalogue of Serials ” as of adhering to the one which has been so long in use. As a Fellow of the Royal Society, I feel very great regret that the Zhurnal; russkoye khimitcheskoye i fisitcheskoye. Council are going to adopt this system in their publications, as it will seriously detract from the value of their supplementary

Hence it is difficult to see why Nizhnii and Zhurnal should be ** Catalogue of Scientific Papers” now in the press, at all events

unintelligible. as far as Russian literature is concerned.

In the Royal Society Catalogue, the Geological Record, and No protest of mine, however, can be half so forcible as the

Chemical Society's Journal, the same name is spelt Jeremejew, unconscious sarcasm of the author himself, in his paper, where Jeremejeft, Jereméeff

. Which of these words represents the he says that ** an expression of grateful thanks is due" to two

pronunciation ? Russians " who have assisted in the arrangement of the system.”

In the Chemical Society's Journal, Wroblewski and Flawitzky The names of the Russians are then given, and if my readers correspond to the Wroblevsky, and Flavitzsky of Armstrong and will take the trouble to study them by the light of the table for Groves' “Organic Chemistry;" transliteration by the new system, he will see how they express where the same Russian letter (and sound) i, denoted both by 28

The same journal frequently quotes the name Markownikoff their appreciation of the author's labours by carefully avoiding and f, while in the examples of Mr. Groves it is also repreevery one of the novelties he has introduced. CHARLES E. Groves,

sented by t'; here, of course, and in similar cases, the name Editor of the Fournal of the Chemical Society.

comes through a German channel. Burlington House, March 17.

Mr. Groves transliterates a few names ; since, however, in his " rational ” system one Russian letter has more than one

English equivalent (2', ), and one English letter (e) has more Having in view the increasing importance of Russian to

than one Russian equivalent, while the sound is not correctly literary and scientific men, it becomes very desirable to have a represented (o, é), it is obvious that this is neither " rational uniform system of transliteration, such as that recently proposed Mr. Groves will now call it the “grapbic method ");

nor a system (it does not profess to be “empirical"; perhaps in your columns. But, in order to be useful, everyone must agree to conform to

Since, moreover, the system recommended by Mr. Groves is is, nor should any such system be adopted off-hand without full that he may yet see his way to adopting the one which has now

not used by him in the Chemical Society's Journal, we hope discussion of any points which may seem susceptible of been accepted by so many of the leading English Societies. improvement.

H. A. M. It seems to me objectionable to indicate the semi-vowels (5 and $) by a simple, and to omit them altogether at the end of a word.

J. W. G. They really correspond, to a certain extent, to our < (mute); and I would suggest that it would be better to indicate them by “Like to Like ”—a Fundamental Principle in Bionomics. a full letter--perhaps i for one and é for the other. March 11.

W. F. KIRBY.

The following letter has been intrusted to me for seeing . through the press, and therefore I deem it desirable to state that

it does not constitute the writer's reply to Mr. Wallace's criticism Oxe or two points in the criticisms on this subject call for of his paper on “Divergent Evolution.” This reply, as presone notice before the publication of a more detaile. account of viously stated (NATURE, vol. xl. p. 645), will be published by the system.

him on some future occasion.

I cannot allow the present communication to appear in these of divergence through segregation states the principle througt columns without again recording my conviction ihat the writer which natural selection becomes a factor promoting sometimes is the most profound of living thinkers upon Darwinian topics, the stability and sometimes the transformation of types, but never and that the generalizations which have been reached by his producing divergent transformation except as it co-operate with twenty years of thought are of more importance to the theory of some form of isolation in producing segregation ; and it man evolution than any that have been published during the post tains that, whenever variations whose ancestors have freely interDarwinian period.

GEORGE J. ROMANES. generated are from any combination of causes subjected to London, March 10.

persistent and cumulative forms of segregation, divergence mere

or less pronounced must be the result. The laws of hereftty. I FOLLOW Prof. Lankester in the use of bionomics to designate which this principle rests may be given in the three following the science treating of the relations of species to species. If statements :the theory of evolution is true, bionomics should treat of the (1) Unlike to unlike, or the removal of segregating influences origin, not only of species, but of genera, and the higher groups is a principle that results either in extinction through failure to in which the organic world now exists.

propagate, or in the breaking down of divergences through free In his very suggestive review of " Darwinism," by Mr. A. R. crossing. Wallace, in NATURE of October 10, 1889 (p: 566), Prof. Lankester (2) Like to like, when the individuals of each intergenerating refers to “his (Mr. Wallace's) theory of the importance of the group represent the average character of the group, is a principale principle of "like to like' in the segregation of varieties, and the through which the stability of existing types is promoted. consequent development of new species.” Prof. Lankester has (3) Like to like, when the individuals of each group represent here alluded to a principle which I consider more fundamental other than the average character of the group, is a principle than natural selection, in that it not only explains whatever through which the transformation of types is effected. influence natural selection has in the formation of new species, In my paper on “ Divergent Evolution" (Linn. Soc. Journ., but also indicates, combinations of causes that may produce Zoology, vol. xx. pp. 189-274), I pointed out that sexual al new species without the aid of diversity of natural selection social instincts often conspire together to bring like to like no The form of like to like which Mr. Wallace discusses is "the groups that do not cross, and that in such cases there will be constant preference of animals for their like, even in the case of divergence even when there is no diversity of natural selection on slightly different varieties of the same species," which is con- the different groups, as, for example, when the different group sidered not as an independent cause of divergence, but as pro- occupy the same area, and are guided by the same labis in ducing isolation which facilitates the action of natural selection. their use of the environment. There is reason to believe than If he had recognized this principle, which he calls selective under such circumstances divergence often arises somewhat in association, as capable of producing in one phase of its action the following way. Local segregation of a partial nature results sexual and social segregation, and in another phase sexual and in some diversity of colour or in some peculiar development of social selection, he would perhaps have seen that its power to accessory plumes, and through the principle of social segregation, produce divergence does not depend on its being aided by which leads animals to prefer to associate with those whox natural selection.

appearance has become familiar to them, the variation is pure Mr. Wallace's view is very clearly expressed in the following vented from being submerged by intercrossing. There met passages, though I find other passages which lead me to think ari es a double process of sexual and social selection, whereby that the chief reason he does not recognize segregation as the both the peculiar external character and the internal iosianet fundamental principle in divergence is that he has not observed that leads those thus characterized to associate together its relations to the principle of like to like. He says :-"A great intensified. The instinct is intensified, because any members body of facts on the one hand, and some weighty arguments on the the community that is deficient in the desire to keep with rı other, alike prove that specific characters have been, and could panions of that kind will stray away and fail of breeding with the only have been, developed and fixed by natural selection because rest. This process I call social selection. The peca Sarity a of their utility” (“Darwinism," p. 142), "Most writers on the colour or plumage is preserved and accumulated, beecke sa subject consider the isolation of a portion of a species a very individual deficient in the characteristic is less likely to surxeo! important factor in the formation of new species, while others in pairing and leaving progeny. This latter process is sexual maintain it to be absolutely essential. This latter view has selection. It can hardly be questioned that both these priacirle arisen from an exaggerated opinion as to the power of inter- are operative in producing permanent varieties and initial crossing to keep down any variety or incipient species, and species; and in the circumstances I have supposed, I do not s merge it in the parent stock'” (“Darwinism," p. 144).

how the process can be attributed to natural selection. Varieus I think we shall reach a more consistent and complete ap- thus segregated may often develop divergent habits in their os prehension of the subject by starting with the fundamental laws of the environment, resulting in divergent forms of matard of heredity, and refusing to admit any assumption that is opposed selection, and producing additional changes; but so long as to these principles, till sufficient reasons have been given. Laws their habits of using the environnent remain unchanged, they which have been established by thousands of years of experiment divergencies cannot be due to natural seiection. in domesticating plants and animals, should be, it seems to me, Mr. Wallace's very interesting section on “Colour 35 : consistently applied to the general theory of evolution. For Means of Recognition," taken in connection with the section example, if in the case of domesticated animals, “it is only by on “Selective Association," already referred to, and anotha isolation and pure breeding that any specially desired qualities on “ Sexual Characters due to Natural Selection," offers 40 can be increased by selection" (see "Darwinism," p. 99), why is explanation of "the curious fact that p ominent differences not the same condition equally essential in the formation of natural colour often distinguish species otherwise very closely alkedIn varieties and species ? Il in our experiments we find that careful each other" (p. 226). His exposition differs from mioc in iha selection of divergent variations of one stock does not result in he denies the influence of sexual selection, and attributos be increasingly divergent varieties unless free crossing be ween the whole process to natural selection, on the ground that ** means varieties is prevenied, why should it be considered an exaggeration of easy recognition must be of vital importance" (p. 217). The to hold thai in wild species " the power of intercrossing to keep reasoning, however, seems to me to be defective, because the down any variety or incipient species, and merge it in the parent general necessity for means of easy recognition is taken 2 stock,” is the same. Experience shows that segregation, which is equivalent to the necessity for a specialization of recognition the bringing of like to like in groups that are prezented from marks that shall enable the different varieties to avoid crossing crossing, is the fundamental principle in the divergence of the In the cases I am considering, there is, however, no adrants various forms of a given stock, rather than selection, which is like in the separate breeding of the different varieties, and even in to like through the prevention of certain forms from propagating ; cases where there is such an advantage (as there would be il the and I think we introduce confusion, perplexity, and a network variety had habits enabling it to escape from competition was of inconsistencies into our exposition of the subject, whenever we the parent stock, but only partially preventing it from crosette assume that the latter is the fundamental factor, and especially with the same), it does not appear how this advantage can per when we assume that it can produce divergence without the co vent the individual that is defective in the special colouring from operation of any cause of segrigation dividing the forms that propa following and associating with those that are more clearly marked gate into two or more groups of similars, or when we assume that The significant part of the process in the development al repagu: segregation and divergence cannot be produced without the airl tion marks must be in the failure of such individuals to SANTE of diverse forms of selection in the different groups. The theory mates, which is sexual selection ; or in the unwillingness of the

community to tolerate the company of such, which might be origin to a quantity of crowded leaves which are long, narrow, alled social selection.

and parallel-sided, and show only a very saint linear striation. It is often assumed by writers on evolution that permanent This plant is identical both in the form and arrangement of the differences in the methods in which a life-preserving function is leaves with that found in the Devonian of Canada, and which I performed are necessarily useful differences. That ihis is not so have named Cordaites angustifolia. I have, however, already toay be shown by an iilastration drawn from the methods of stated in my Reports on the Flora of the Erian of Canada langunge. The general usefulness of language is most apparent, (Geological Survey of Canada, 1871 and 1882), that I do not and it is certain that sople of the laws of linguistic development consider this plant as closely related to the true Cordaites, and are determined by a principle which may be called "the survival that I have not changed the generic name merely because I am of the fittest;" but it is equally certain that all the divergences still in doubt as to the actual affinities of the plant. Mr. Reid's which separate languages are not useful divergences. That one specimens would rather tend to the belief that it was, as I have race of men should count by tens and another by twenties is not already suggested in the reports above cited, a Zostera-like determined by differences in the environments of the races, or by plant growing in tufts at the bottom of water. any advantage derived from the difference in the methods. So Some of the sandstone slabs from Murthly contain specimens easy recognition of other members of the species is of the highest of rounded objects reserable to Fachytheca (Hooker), a genus importance for every species; but difference in " recognition of uncertain affinities but characteristic of Silurian and Lower marks" in portions of a species separated in different districts of Devonian beds on both sides of the Atlantic. One of these is the same environment is no advantage. Under the same condi- perfectly spherical with a shining surface, and 275 mm. in diations, habits of feeding may become divergent ; but, since any meter, the others have been broken so as to show a central new habit that may be found advantageous in one district would cavity or nucleus about i mn. in diameter, and with a thick te of equal advantage in the other district, the divergence must carbonaceous wall partly pyritised and showing obscure radiating be attributed to some initial difference in the two portions of the fibres. Prof. Penhallow, of McGill University, has kindly exspecies.

amined these, and has compared them with slices of Pachytheca I have recently observed that, of two closely allied species of from the Wenlock limestone, kindly communicated by Mr. fiat-fish found on the coasts of Japan, one always has its eyes Barber, of Cambridge, and with specimens presented by Prof. on the right side, and the other always on the left. As either Hicks from the Silurian of Corwen and with specimens in the arrangement would be equally useful in the environment of either author's collection from the Silurian of Cape Bon Ami; and species, the divergence cannot be considered advantageous. also with the excellent figures in Mr. Barber's paper in the Osaka, Japan.

JOHN T. GULICK. Annals of Botany. He has not been able, however, to arrive at

any conclusions beyond the probable general similarity in strucSelf-Colonization of the Coco-nut Palm.

ture of the various forms, which may, however, as Mr. Barber

suggests, have differed in their nature and origin. The only THE question whether the coco-nut palm is capable of thing certain at present seems to be that these puzzling establishing itself on oceanic islands, or other shores for the organisms had a thicker outer coat of radiating fibres, and of so matter of that, from seed cast ashore, was long doubted; and if great density that it was less liable to compression than the the recent evidence collected by Prof. Moseley, Mr. H. o. other vegetable tissues with which it is associated. Forbes, and Dr. Guppy, together with the general distribution of A few small specimens sent more recently by Mr. Reid conthe palm, be not sufficient to convince the most sceptical person tain some curious but not very intelligible objects from the same on this point, there is now absolutely incontrovertible evidence beds. One is a stem coiled at the end very closely in a circinate that it is capable of doing so, even under apparently very manner. In form it resembles the circinate vernation of unfavourable conditions.

Psilophyton princeps, but is much larger. It may belong to P. la the current volume of NATURE (p. 276) Captain Wharton robustius, or possibly to a sern, but is too obscure for certain describes the newly-raised Falcon Island in the Pacific ; and in determination. Several others appear to represent flattened the last part of the Proceedings of the Royal Geographical fruits or sporangia of obovate form and of large size. One has Society, Mr. J. J. Lister gives an account of the natural history of a stalk attached with what seems a rudiment of a bract, and the island. From this interesting contribution to the sources of another shows obscure indications of having contained round or insular floras we learn that he found two young coco-nut palms, disk-shaped bodies about 2 mm. in diameter. All show minute not in a very flourishing condition, it is true ; but they were longitudinal striation. I have not previously met with bodies of there, and had evidently obtained a footing unaided by man. this kind in the Devonian, and can only suggest that they may *There were also a grass, a leguminous plant, and a young represent the fructification of some unknown plant, possibly that candle-nut (Aleurites), on this new volcanic island-a very to which Pachytheca belonged.

J. Wm. Dawson. good start under the circumstances, and suggestive of what Montreal, March 5. might happen in the course of centuries. W. BOTTING HEMSLEY.

Exact Thermometry.
On Certain Devonian Plants from Scotland,

I am glad to observe that Prof. Sydney Young and myself

are now in substantial agreement as regards the tension theory I AM indebted to Mr. James Reid, of Allan House, Blair of the ascent of the zero in thermometers, and approximately gowrie, Scotland, for the opportunity to examine a collection of in agreement as regards the actual cause of the ascent in the lossil plants obtained by him from the Old Red Sandstone of neighbourhood of the ordinary temperature. Murthly and Blairgowrie in Perthshire, some of which have Some time ago, in connection with an investigation of melting. been noticed by Dr. Geikie in his “ Text-book of Geology." point, I devoted three years to an examination of the properties

The collection is remarkable for the striking resemblance of of the mercurial thermometer. Among other conclusions which the matrix and the contained vegetable debris to those of the then seemed to me probable, the application of the known lower part of the Gaspé sandstones of Logan, and the species of plasticity of glass under pressure to account for the enormous plants are, so far as can be determined, the same.

ascent (in lead-glass) of the zero at high temperatures Prilopkyton princeps largely predominates, as in Gaspé, and appeared of some value. I have never advanced it as a mature is represented by a profusion of fragments of stems and branches, theory, and am perfectly open to correction on the subject ; but and more rarely by specimens of the rhizoma and of the neither Prof. Crafts (with whom I at that time discussed the sporocarps. P. robustius is represented by fragments of stems, matter), nor any subsequent experimenter, has submitted the but is less abundant, and Arthrostigma gracile hy some portions suggestion to a crucial examination. sf stems. On the whole the assemblage is exacily those of the Prof. Young's experiments (NATURE, March 27, p. 489) are very sandstone beds of the lower division of the Gaspé sandstones. interesting as far as they go ; but the kind of glass of which his There is nothing distinctively Upper Devonian in the collection. thermometers are constracted is not that which brings out the

The collection also contains two slabs of dark-coloured peculiarities of the material in their most striking developsandstone from Caithness, one of which contains what appears ment. This, indeed, has long been known. It may well be that, to be a fern stipe similar to those of the genus Rhodea. Another in German soda-glass, the plasticity is masked by a preponderatshows a remarkable plant having apparently a short stem giving ing tendency of the harder or more crystalline silicates of the * See papers by the author, Journal Geol. Society, London, 1859, and

bulb to set. Much could be done towards settling the question Prooeedings Geol Society, Edinburgh, 1877.

as to plasticity, if three thermometers of lead-glass-one vacuous,

one open to the air, and one with air sealed in--were heated Sheepshank's comparisons, and adhering to the Clarke value together and successively to 100° C., 120°, 150°, 200°, 250°, 270°, 39*3704+ inches, deduces the (the writer of this thinks) erroneous and 3coo, and the zeros observed. Even then, there still would conclusion, that the space on the Shuckburgh scale quals remain to be explained the strange depression which I noticed 39-400428 inches, the value according to their comparisons in several sealed thermometers of lead-glass in the neighbourhood being 39*399896 inches. If to this value be added o'opogo incl. of 270°. At present, I regard the suggestion as neither proved the amount by which the distance het ween the knife-edge of nor disproved.

the Kater pendulum exceeds the space 0-394inches, the resulting We are, in fact, only beginning to learn what silica and length of the Kater pendulum at 1667 C. is 3944080 inches, silicates are. I have quite lately, for example, found a critical a value practically identical with that published by Kater, which point in the action of heat upon fire-clays, similar to the 270° is 39 44085 inches. point in the zeros (before referred to) of my lead-glass thermometers; and a similar point is known to exist in the

The Green Flash at Sunset. relation of the refractive index of quartz to temperature. Results of this kind sh w clearly that thermometry is by no

The explanation of the bluish (?) green Aash of light some means an easy subject. Indeed, I might define it as a mixture times seen at sunset given in your note last week (p. 4951 does not of very complicated chemistry with very complicated physics.

seem to me to be a sufficient explanation of all the observations Glasgow, March 28.

EDMUND J. Mills.

If the phenomenon were due simply to refraction it would last for only a fraction of a second, and the colour would be muca

more blue than green. But, so far as my own observations go, The Shuckburgh Scale and Kater Pendulum.

the colour may last for several seconds, and is a bright per By permission of Prof. T. C. Mendenhall, Superintendent green, exactly similar to that shown by the sua many degrees of the United States Coast and Geodetic Survey, and of above the horizon in South India in Sextember 1883. To Weights and Measures, I enclose to you for publication, if produce that green, as I have shown elsewhere, all that is deemed suitable, a note relating to an abstract of a paper by required is the absorption due to a great thickness of vapour, General J. T. Walker, R. E., F.R.S., published in NATURE combined with a certain amount of dust-water dast or other of February 20 (p. 381).

| I saw a very pretty example of this last July when or the As the subject matter refers to U.S.C. and G.S. Bulletin coast of Vancouver, B.C. The air was very moist and the rainNo. 9, I take the liberty of enclosing it also.

band correspondingly strong, while fine dust was supplied hy

0. H. TITTMANN. the lad breeze carrying with it particles from the burning United States Coast and Geodetic Survey, Office of Weights forests inland. The sky was cloudles, but the haze was thick and Measures, Washington, D.C., March 13.

enough to allow one to look at the sun while it was still some Last summer the United States Coast and Geodetic Survey degrees above the horizon, and the disk appeared of a brilliant published an investigation, Balletin No. 9, on the relation of golden-red, gradually changing to yellow, and, finally, wlule the yard to the metre.

part was still above the horizon, it became a bright pea-greca As the result of this investigation, values were deduced for

The spectrum was similar to that figured in my paper on the the length of certain historic standards in England which green sun (R.S.E. Trans., xxxii

. 389). differed very materially from the values previously assigned to

A few days later I had a view of the sunset from the Selkirks, them in metric measures.

where the air was very dry, the rain-band slight, but the ha Thus the length of the Royal Society's platinun metre, brilliant, and never passed beyond the stage of a reddish-copper

considerable. The colours of the sun's disk were much less certified by Arago to be 17.59 u too short, was found to be only tint. 7 u to short.

Č. MICHIE SMITH. This metre was compared by Captain Kater with a certain

73 George Street, Edinburgh, March 31. space (0-39 4 inches) on the Shuckburgh scale, and this space was in turn compared with his pen.lulum. It is therefore of

Foreign Substances attached to Crabs. interest to know whether the value deduced in the investiguion referred to is accurate. It is the object of this note to call I must of course accept Prof. McIntosh's interpretation of attention to a surprising verification of the de luctions contained his own statement, and admit that he has found Molgula areas in Bulletin No. 9. Using the equation for the platinum metre frequently in the stomachs of Cod and Haddock. This Ascidian found in that paper, namely

differs from the majority of its class ia having allocryptic lahiu, Platinum Metre = 1 m. - 7M +9'126 , 1 C°,

but I have not yet made a sufficient number of experiments to we find

be satisfied as to its edibility. It has also been a considerable at 15° :98 C., P.M. = 1 + 138 8u;

difficulty to me that the extensive investigations of Brook and

Ramsay Smith lend no support at all to the opinion that ths but at this temperature Captain Kater found the space on the Ascidian forms an article of food for ground-feeding fisk. le Shuckburgh scale

any case the matter, though of much interest, is not one fer (0-39*4 inches) = P.M. + 0'02400 inch, or 06096 mm., whence the space in question of the Shuck burgh scale substances attached to crabs."

discussion here, since Molgula arenosa is never one of the **foreigo = 1 '007484 m., and using for the coefficient expansion The statement made by Mr. IIolt that " Actinia menembry 18-85 x 10-6 for 1° C., we have at 16°:67

anthemum is a favourite food of the Cod," was so inconsistent the space = 1'0007614 m.

with our knowledge of the habits and distribution of the two NATURE of February 20 (p. 381) publishes an abstract of a

species that, as I expected, the grounds for his assertion prove paper by General J. T. Walker, R.E., F.R.S., "On the Unit offensiveness of Actinians to fishes was made after prolonget

to be entirely fallacious. My statement with regard to the of Length of a Siandard Scale by Sir George Shuckburgh, observation of the habits of the living animals and after ex appertaining to the Royal Society," in which he states that the Shuckburgh scale was taken to Paris and compared with the St. Andrews fishermen find A. mesembryanthemum to be *

periment, while Mr. Holt bases his objection on the ground that one of the standard bars of the International Bureau of successful bait for Cod. One might as well argue that because Weights and Measures, by Commandant Defforges. The result of this comparison reduced to 16°67 C., and as given by in whiffing for Mackerel, therefore these substances forma

bits of red flannel or of tobacco pipe are highly successful baits General Walker is

" favourite food" of this fish. A moment's reflection ako the space = 1'0007619 m.

would have shown Mr. Ilolt that an Anemone impaled upon a list This agreement is perfect, more so, in fact, than the circum- hook is a much less dangerous creature than one under natural stances allow one to expect,

conditions and with tentacles expanded. The agreement implies the correctness of the new values During the past week an interesting observation of Eisig's has deduced in Bulletin No. 9 for the Ordnance metre and the come under my notice which corroborates the view that the platinum metre of the Royal Society, and gives the value of the association between Crabs and Anemones is of primary importmetre as equal to 39-3699 inches as therein computed from ance for the protection of the Crabs. Eisig observed (see jour. Baily's and Sheepshana's comparisons, which established the R.M.S., iii., 1883, p. 493) that an Octopus in iis attacks up relation between the Imperial yard and the space on the Hermit Crab would instantly retreat upon being touched by the Shuckburgh scale.

stinging organs of the Actinian associated with it. It is to be noted that General Walker, igaoring Baily's and Plymouth, April 5.

WALTER GARSTAND

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