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It will be fresh in the memory of many of our readers THURSDAY, OCTOBER 5, 1871

that during the month of October last year, very remarkable and brilliant “auroræ ” were observed in London, chiefly of a deep blood-red colour, spreading from the

zenith over a great portion of the heavens. OBSERVATIONS UPON MAGNETIC STORMS It is, however, in the more northern latitude of the IN HIGHER LATITUDES

Orkney and Shetland Islands that the grandeur of these

wonderful electrical phenomena can be observed, and that THI 'HE extension of the telegraph into the more northern

reliable data can be obtained from which hereafter some latitude of the Shetland Islands, between 59° 51' and 60° 51' 30" N., has afforded a much better opportunity of practical result may be deduced.

As observed in Orkney and Shetland, the aurora, as a observing the frequency and variation of the magnetic and auroral storms that have of late excited some atten- general rule, appears to concentrate and emerge from tion and discussion in these pages.

behind a dense mass of dark cloud lying low down in the Some of the earliest recorded observations upon the horizon towards the north. The edge of this cloud-bank

is serrated strength and direction of these atmospheric storms, date

nd jagged, as if the mass were electrically in from the time when the extension of the telegraphic wires

a high state of tension. From behind this cloud-bank over England rendered the phenomenon visible by the

“dark" streamers will appear to start up high into the disturbance of the magnetic needle placed in circuit with zenith, appearing as if attenuated portions of the edge of the wires, and to a certain extent rendered possible the the cloud-bank had been dragged by some invisible power, mapping down of the position and direction of the mag

these dark auroral rays being at the same time transparent netic storm over certain tracts of Great Britain.

as regards the power of transmitting the light of the stars, On the 24th September, 1847, remarkable magnetic which shone through with undiminished splendour. At disturbances were observed in London, and the direction the same moment that these dark rays are emicant, and deflection of the magnetic needle noted. The effects brilliant green, violet, crimson, and white rays appear to of this magnetic storm were carefully observed at Daw- stream upwards towards the zenith, but always with a less lish, Norwich, Derby, Birmingham, Rugby, Cambridge, persistence of duration. These coloured scintillations Tonbridge, Wakefield, Edinburgh, and York. The mag

change with greater rapidity than the black rays. netic disturbance appears to have commenced about

During the month of December of last year, some very Ih 5m P.M. on the 24th, and continued with variable in- vivid prismatic tints were observed from the Island of tensity until 71 3011 A.M. on the 25th.

Eday. From careful observation it was then remarked It may be interesting to give some of the galvanometer that the red coloured rays appeared generally to be of a readings recorded as indicating the rapid oscillation and partially opaque nature, and it could be readily seen that deflection of the galvanometer needle. In the period of the light of a star, when viewed through the red scintillatime between 4" 17" P.m., and 5" 48" P.M. on the 24th, or tion, was dimmed as compared with the brilliancy of the in about one hour and a half, the direction of the cur

same star when observed through the scintillations of

another colour. rent had changed no less than ten times, showing a maximum swing of the needle over an arc of 50°.

In some of these displays, the most vivid and varied

colouring was exhibited. These were noted down as deg.

deg.

visible to the eye at the same time, and as the colours 4.17 5.5

were observed in contrast, the distinctiveness and 4.20 20 right

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brilliancy of the tint became the more decided. Black, 4.25

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18 left pale yellow, strong yellow, white, violet, pale blue 4.35 6 5.25 14 right

bright green, crimson shade fading into a reddish pink, 4.38

pale orange, and a delicate sea-green tint. So far no4.45 5.32

thing approaching to the indigo hue has been noticed. 4.50 jo left

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With this exception, the entire prismatic colours and 4.51

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blending tints may be said to have been perfectly deve4.56

loped in the rapid electrical scintillations of the aurora.

The colours fade away and change with astonishing During this magnetic storm, the variation of the dipping rapidity, and this variation in tint will take place without needle which was observed in London every 30", ranged apparently any great electrical disturbance in the special between 69° 30' and 67° 50'.

ray observed, beyond a slight flickering motion. In these In some cases these magnetic storms were so severe as regions, where the atmosphere is so perfectly still and at to impede the working of the railway signals. On the times calm, repeated observation has determined the exist18th of October, 1841, a very intense magnetic disturbance | ence of very appreciable sound to the ear, as an accomwas recorded, and amongst other curious facts mentioned panying phenomenon (to the rapid rush of the auroral is that of the detention of the 10.5 P.M. express train at streams towards the zenith. The intensity of the sound Exeter sixteen minutes, as from the magnetic disturbance emitted varies considerably. At times, it greatly resembles affecting the needles so powerfully, it was impossible to that of the rushing noise caused by the firing of a rocket ascertain if the line was clear at Starcross. The superin- into the air when reaching the ear from a distance. At tendent at Exeter reported the next morning that some other times it has a strong resemblance to the sound proone was playing tricks with the instruments, and would duced by the crackling of burning embers, but wanting in not let them work,

any very distinctive sharpness. VOL. IV.

H. M.

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In all these cases of auroral displays the inductive

THE LIGHT OF JUPITER'S SATELLITES effects upon the telegraph wires are very strongly marked ; currents of varying intensity and direction flowing un

Ueber die Helligkeitsverhältnisse der Jupiterstrabanten, von ceasingly through these metallic circuits.

Dr. R. Engelmann, Observator der Sternwarte zu LeipThe result of observations made in Shetland during the

zig. (Leipzig ; London : Williams and Norgate. 1871.) months of September

, October

, November, and December
, ,

O the retinue of the sun, none, when we have left our own attained their maximum effect upon the wires between moon behind us,promises such a reward for investigation as gh 30" and 9h 30M A M., and between 8h 301 and 1030P.M.; that of the planet Jupiter. The remoter ones may be, and and such is the unstableness of these induced auroral cur

probably are, intrinsically of a more remarkable characrents, that frequently in five minutes the electromotive force ter, but they are, and ever will remain to a great extent, will vary from very much less than that of a Daniell cell beyond our reach ; while the attendants of the largest to a current of such intensity that a brilliant stream of among the planets are numerous enough to interest by inlight will flash across the points of the lightning conductors dividual peculiarities, which their comparative proximity with sharp detonating reports, the electromotive force of enables us to study with advantage. Yet it is readily which would be scarcely equalled by 500 Daniell cells. observable that though ordinary telescopes of good quality

In January last very curious electrical phenomena were would have done much towards elucidating their phenoobserved at Lerwick through the day-time, in connection mena, very little progress has been made in the inquiry, with the N.E. gales so prevalent at that period of the year. I especially in this country ; and the work now before us is In Shetland these gales are almost withoutexception accom- the first attempt to collect and to make serviceable the panied with very severe hail-storms. The day begins bright scattered observations which exist, of which we are sorry and fine, a clear sky, the barometer rapidly rising ; low on to remark how few are due to the astronomers of Eng. the horizon may be observed dense and angry-looking clouds. land. One by one these clouds travel fast towards the zenith, The especial object of the eminent observer at Leipwhen all at once a fearful gust of wind, accompanied with zig has been not the theory of the motions of these the most violent hail-storm, will apparently break out of satellites, but simply their physical aspect in regard to the the cloud, and continue for about fifteen minutes. The variable light which they have long been known to rewind then subsides, and the day appears as fine as before. flect, and to this investigation the author, notwithstanding In half an hour's time a second cloud will have appeared, constant engagement in important zone observatio 1s, has and there will be a repetition of the temporary tornado contributed far more than all who have preceded him. and hail-storm. The remarkable circumstance attending The instrument which he employed was the astrophotothese successive storm clouds is that they appear to be a meter of Zöllner. In this ingenious contrivance, the light purely electrical phenomenon. The moment that the icy of the object to be examined is referred to that of one or discharge takes place from the cloud with its accompany- more known comparison stars, by means of an artificial ing “ crack" of wind, an induced electrical current appears star produced by a petroleum flame, adjustable for brightupon the wire, so strong that it attracts firmly down the ness and colour by a Nicol prism, and a colorimeter," armatures of the telegraph Morse apparatus. The or revolving wheel of tinted rock-crystal. But in order to moment, however, that the hail ceases, the current passes eliminate the effect of unequal areas, so as to ascertain, off, but with this result, that each successive cloud storm not merely the absolute amount of light reflected, but the appears to induce a current flowing inan opposite direc- 'albedo," or reflecting power of each surface, it is, of tion from the last, that is to say, the currents appear to course, necessary !o obtain reliable measures of these be (using conventional language) positive and negative in minute specks of light ; and in order to decide the their effects.

interesting question whether or not their rotation That these storms are “ electrically excited" there is no and revolution are, as with our own satellite, syn. disputing, and that they occur during the prevalence of chronous, their anomalies, or orbital positions relative the chief auroral displays is also a matter of observation, to their primary, have to be taken into account. but so far their connection with aurora has not been this has been done with most praiseworthy care; the sufficiently determined to permit any opinion to be ex- whole is discussed and reduced with scrupulous and pressed

exemplary attention to every possible source of accidental The recent successful completion of the telegraph error; and the result is given to the eye in several elabocircuit to Shetland, and the extensions immediately to be rate diagrams. We shall merely specify some of the concarried out one hundred miles farther north, will afford clusions, which will be found of considerable interest to much greater facilities for auroral observation than has astronomers. The absolute brightness was found by the hitherto existed. It is also proposed to institute a careful author, as it has been by all previous observers, very spectroscopical examination of the coloured scintillations ; variable ; and from the irregularity and occasional rapidity and now that the Meteorological Society are about to of its changes, it becomes impossible to decide, in the case establish an observation station in Shetland, there is every of the three interior satellites, whether the periods of prospect of some valuable data being collected on this rotation and revolution are identical. interesting subject, which may hereafter guide our meteoro- appears to be decidedly the fact with the outermost. logical students in arriving at some satisfactory conclusion Herschel I. had extended the inference to all of them ; regarding the laws of electrical storms and auroral induc. but such a result could not now be accepted ; and it seems tion. At present we are only able to record a few care probable that the spots which must occasion these variafully observed facts.

tions, and which have been repeatedly noticed when the

All

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OUR BOOK SHELF and Secchi even in other positions, may be of changeable Transactions of the Geological Society of Glasgow. Vol. character. At a mean II. is relatively the most, IV. the

III. Supplement. On the Carboniferous Fossils of the least luminous. As to their micrometrical measurement, West of Scotland : their Vertical Range and Distribution. every one who is acquainted with the telescopic aspect By John Young, Vice-President. With a General Catathese minute discs will readily comprehend its difficulty. logue of the Fossils and their Mode of Occurrence, It has, however, been attempted in various ways, but not

and an Index to the Principal Localities. By James

Armstrong, Honorary Secretary. (Glasgow, 1871.) by the double-image micrometer, which does not seem to have been used ; the results, as may be expected, pre

This catalogue of fossils will doubtless be of great use sent considerable discrepancies, but the final values ob

not only to local geologists, but to others at a distance, who tained by a combination of different methods in the hands may desire to compare the treasures of English and Irish

Carboniserous strata with what the equivalent beds in Scotof various observers are as follow :-1., 1":081 ; II., o":910; land have yielded. So far as they go, the lists appear to III., 1"537 ; IV., 1"-282 ; or, in English miles, 2,498, 2,102, be drawn up with considerable care, and Mr. Armstrong 3,551, 2,962, the solar parallax being taken as 8''90. is to be congratulated upon the result of what must have These values, all things considered, differ so little from those been somewhat laborious work. But we are sure he will given by Lockyer (Guillemin's “Heavens”) — namely, to be done before the Scottish Carboniferous fora and

be the first to admit that much, very much, still remains 2,440, 2,192, 3,759, 3,062—that we may consider ourselves fauna can be satisfactorily compared with those of other possessed of a very fair approximation to their real mago countries. We are constantly being reminded throughout nitudes,

this catalogue that not only in private collections, but also Astothe “albedo” of their surfaces, I. shows no great varia. in public museums in the West of Scotland, there are tion; it falls, according to Zöllner's estimate of the reflective numbers of specimens under almost every class waiting power of terrestrial materials, between that of marl and white believe that not a few are species new to science. This,

to be identified, amongst which there is every reason to sandstone ; II. has the greatest variations of albedo, which it seems, is specially the case with the plants, the rich at a mean somewhat exceeds that of white sandstone ; III., flora of the Carboniferous period being represented in the the variations of which are smaller and more regular, comes catalogue by only ninety species. But Mr. Carruthers, between marl and quartzose porphyry; IV., which varies

we are told, has several undescribed specimens in hand, of least, equals that of moist arable land. It will probably it would appear, also need looking after.

which we shall, no doubt, hear by-and-by. The fishes,

There are be thought, however, that curious as these comparisons eighty-four species, under forty genera, named in the may be, the standards are much too uncertain to give any catalogue ; but a large number in various collections have satisfactory result. As to colour, Dr. Engelmann, after never been correctly identified with described species, and citing the elder Herschel's estimates--1., white ; 11., white, Mr. Young expresses a hope, in which we cordially join; bluish, and ash-coloured ; III., white; IV., dusky, dingy, that Prof. Young will be induced to prepare a special inclining to orange, reddish, and ruddy-specifies as the catalogue of these and the Reptilia, of which only seven determination of other observers : l., yellowish ; 11., white species are given by Mr. Armstrong. The other classes

are represented as follow's :-Foraminifera, 2 genera, 4 or yellowish ; III., intensely yellow with low powers ; IV., species ; Hydrozoa, i g. 2 sp. ; Zoophyta, 22 g. 59 sp. ; in achromatics a distinct dusky blue. (These colour. Echinodermata, 6 g. 15 sp. ; Annelida, 4 g. 7 sp. ; Crusvalues at any rate afford no countenance to the common tacea, 19 g. 71 sp. ; Insecta, 2 g. 2 sp. : Polyzoa, 11 g. impression that Herschel had a bias for red tints.) To 36 sp. ; Brachiopoda, 15 g. 50 sp.; Lamellibranchiata, the writer, whether with two achromatics, or a nine-inch 28 g. 127 sp. ; Pteropoda, i g. 1 sp.; Gasteropoda,

15 g. 75 sp. ; Cephalopoda, 6 g. 46 sp. From these silvered mirror, this satellite has always appeared ruddy numbers it will be seen that the collectors have not been when its colour has formed the object of notice ; in such idle, and, no doubt, Mr. Armstrong's catalogue, with its discrepancies something may be instrumental, something minute index to localities, will be the means of sending subjective. It is pleasant to see here a very full appreci- many to hunt in quarters which they have not already ation of the laborious perseverance and honest accuracy conditions under which the fossils are distributed, and not

visited. Let us hope that they will note something of the of the labours of Schröter, to whose merit time seems to

content themselves simply by bringing away good bags be doing tardy justice ; no notice is taken, however, of the full. Collectors cannot be too often reminded that it is of observations of Gruithuisen, who twice appears to have more importance, in the interests both of natural history seen spots on III on the background of the sky; nor is and geology, to know one limited district thoroughly, reference made to the irregular shape of that satellite re

than to go roving over half a country merely for the purmarked by Secchi and his assistant ; nor to the apparent should mark out for himself some practicable area, and

pose of picking up finely preserved specimens. Each discrepancy which has often been noticed between the make it his endeavour to search every bed, even the most unmagnitudes of the satellites and their shadows. Still, the promising, noting not only the fossils he meets with, but treatise may be considered as very nearly an exhaustive the character of the strata in which they occur. He should one ; and a most important and acceptable contribution also observe what effect a change in the character of a to planetary astronomy. It may be added that it contains bed has upon the fossils it may happen to contain; whether a very valuable determination of the telescopic magnitude vidually gain in size or become dwarfed, and, should cer

they increase or decrease in numbers, whether they indiof Jupiter, from the average of eleven observers ; the re. tain species disappear, what others, if any, are substituted sult being, with the double-image micrometer 37":609 for for them. It is only by marking carefully such points as the equatorial, 35"-236 for the polar diameter; with these that we can ever hope to acquire an adequate conthe wire micrometer, 38"-312 and 35"-914: the former çeption of the natural history of the old carboniferous values, which he seems to prefer, exhibiting a flattening lands and seas. Mr. Young is quite sensible of the short

comings of the collectors in this matter, and gives them T. W. WEBB some seasonable advice, which it may be hoped they will

take to heart. If collectors paid better heed to these

:

of 1

15.82.

matters they would assuredly derive greater pleasure and | tical periodical, is very different from the investigation of one out profit from their pursuit, and do much more towards the of a chain of propositions in a mathematical treatise. In the progress of science. Mr. Young himself, however, not- former case there are no antecedent or subsequent conditions to withstanding the good advice he gives, is not always care

regard ; in the latter case we have to consider what agrees best ful in drawing conclusions, geological evidence being some

with the whole scope of the work, with what is to follow as well times quite overlooked. Thus, we find him stating that

as with what has gone before. A writer, after arranging a para: the coal-measures (meaning, of course, the whole series graph or a chapter in what seems the best manner, may find of strata above the Millstone Grit) are "evidently of land would have been unnecessary, perhaps even undesirable, if the

himself constrained at a subsequent stage to make changes which and fresh-water origin,” because they have yielded no earlier portion had stood alone. Then, if a reader opens the marine organisms, save in one thin local bed near the top book at random and criticises a passage without any regard to the of the series. The occurrence of this stratum with its author's sense, the criticism may very naturally be quite inapmarine remains, indicates, as he believes, the return for a propriate. short time of the sea, which had for a very long period There is, however, a very important consideration of another “ been completely shut out by barriers." "Mr. Young is kind which has been frequently disregarded, but which is pressed welcome to his belief. If every bed or series of beds in upon our notice by the interest at present felt in geometrical which no marine organisms occur must necessarily be of studies. Let us determine the reason which leads us in some, or fresh-water origin, the lakes of old must have been some

in many, cases, to prefer a solution which involves only the third thing worth seeing. There are several points suggested

book of Euclid to a solution which depends on the sixth book ; by the catalogue that we should like to have taken up, but

this, I apprehend, is merely a persuasion that Euclid's order is a

natural order, so that in a well-arranged system the propositions our space is exhausted, and we can only conclude by

of the third book ought to precede those of the sixth book. I strongly recommending Mr. Armstrong's work to the

am of this persuasion myself ; I think that no scheme can be notice of our geological readers.

J. G.

perfect, and, on the whole, I am well satisfied with Euclid's. But there are places where Euclid is strong, and there are places where Euclid is weak; and the position which he has assigned

to the last three propositions of his third book, must rather be LETTERS TO THE EDITOR

classed with the latter than with the former. His object, of The Editor does not hold himself responsible for opinions expressed pentagon, and we cannot be surprised at the introduction of that

course, must have been to lead up to his construction of a regular by his Correspondents. No notice is taken of anonymous remarkable process. But I have always envied the advantage in communications. ]

this respect to be claimed for the non-Euclidean systems, which On the Solution of a Certain Geometrical Problem

transfer these propositions and place them aster the doctrine of

similar triangles ; thus the long and rather artificial treatment A WRITER in the number of NATURE for September 21, Mr. which they receive from Euclid is superseded, and the proposiR. A. Proctor, in the course of a letter on the state of geometrical tions become almost intuitive. Hence, in fact, if we have re. knowledge in the university, alludes manifestly to the solution of course to the sixth book of Euclid when we might have accoma problem which I have adopted in my edition of Euclid. The plished our end by the aid of the first thirty-four propositions of matter is of small importance in itself, but nevertheless as some

the third book, we may be fairly liable to the charge that we have points of interest are incidentally involved, I request you to not adopted the simplest and most natural method ; but the last állow me the opportunity of offering a few remarks. The problem is this : to describe a circle which shall pass

three propositions of the third book are quite different in kind

from the others, and instead of using them, it may be really as through a given point and touch two given straight lines. Your simple and as natural in many cases to use the principle of correspondent considers that in giving a solution which depends similar triangles. on the sixth book of Euclid, instead of one which depends only

I shall be obliged to any person who may be skilled in prac: on the third book, I exhibit signal geometrical weakness.

tical geometry if he will state what he considers the best method The problem, I need scarcely say, is very old ; indeed, so old that a writer who had been long engaged in teaching could not

of actually solving the problem, supposing that both circles are

to be determined which satisfy the conditions. I assume that pretend to solve it afresh, for he would certainly have in his we have the aid of compasses and also of one of the ordinary memory one or more solutions which had become quite familiar contrivances for drawing parallel lines. This is a matter of some to him. The solution by the aid of the third book is well

interest, though of course unconnected with the theoretical solu. known, for it occurs in several of the collections of geometrical tion of the problem. exercises. The solution which I have adopted is also old, but I should be glad to make some remarks on the general subject seems not so well known. It is, I think, conspicuous for sim- which led to the notice of the particular problem I have discussed, plicity, elegance, and completeness. The demonstration is of but at present I have not sufficient leisure. I must content my; the best and most impressive kind, requiring no laborious effort self with having shown that the course into which I am supposed to understand and retain it, but being almost self-evident from

to have dristed by geometrical incapacity, was adopted deliberately the diagram. Even if the problem be treated as an isolated exer- under the guidance of reasonable geometrical knowledge. cise, the solution which I have preferred will sustain a favourable

I. TODHUNTER comparison with that which more commonly occurs.

St. John's College, Cambridge, Oct. 2 But the determining cause of my choice was the position which the solution occupies as one of a connected series. I have just before treated a similar problem by the third-book method,

Structure of Fossil Cryptogams so that if the same method had been used for the present problem, It was unfortunate that at the recent meeting of the British there would have been only repetition without any substantial Association, Prof. Williamson's paper had to be discussed in a increase of knowledge; whereas by the course adopted the very hurried manner, and he is, no doubt, justified in taking care student is introduced to fresh and valuable matter. The principle “that there shall be no misunderstanding as to the real point at of similarity and the notion of a centre of similitude are most issue.” I do not think that he has brought it out very plainly instructively involved, and the student is prepared for a subse- in his paper in NATURE, and perhaps, as he mentions me as an quent investigation, which is similar but more complex. To opponent of his views, I may be allowed to state precisely in sum up, the third-book method would have constituted no advance what respects I differ from him. in the subject, where the sixth-book method takes a step im- First, as to matters of fact. Prof. Williamson speaks of the portant in itself and in its consequences; and therefore, following central structure of the stems of the extinct Lycopodiaceæ as a the example of an eminent geometer, I adopted the latter method. “vascular medulla,” by which he explains that he means a I may perhaps venture on the strength of my own experience as structure containing vessels," and that there shall be no misto the utility of the solution, to recommend it to the attention of apprehension he adduces Nepenthes as possessing it ; the instance other teachers.

is a well-known one, and leaves no room for doubt as to Prof. It is very important to bear in mind the distinction between Williamson's meaning. Now from the examination of specimens, what I may call absolute and relative merit which I have just and of the drawings of them published by Mr. Carruthers (the exemplified. The solution of a single problem furnished by a accuracy of which I believe Prof. Williamson does not dispute) candidate under examination, or by a contributor to a mathema- I am quite satisfied that the central structure consists wholly of

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scalariform vessels, and that there is in fact nothing medullary or

The Solar Spectrum medulla-like about it. Outside this central structure is what Mr. Carruthers terms

MAY I venture to suggest that quite possibly something of the investing, and Prof. Williamson the vascular woody cylin- value might be obtained by observing the sun during totality with der, I believe that Mr. Carruthers is right in looking upon

a spectroscope of reasonable dispersive power (say four or five

prisms) without a collimator, or even simply with one of the so. this as belonging to the central axis, which is therefore composed of two parts. I find, which I did not sufficiently appreciate at

called meteor spectroscopes.

If the bright rays and rists are really and simply (or even the time, that Prof. McNab regards this investing cylinder as homologous with the cylinder of wood cells surrounding the give a well-defined green image ; if they are formed by reflection

mainly) composed of the green-line.giving substance, they will central axis of fibro-vascular bundles which is met with in many recent Lycopodiaceæ. From this I certainly dissent for (either at the sun or in our atmosphere) of ordinary sunlight, they

would be so dispersed as to be invisible or nearly so, and if two reasons ; (1) because I think its equivalent is to be found in the central axis itself, and not outside it; (2) because it is not com

formed by the reflection of chromosphere light they would give

several images, the red (C) and blue-green (F) being most conposed of wood cells but of scalarisorm vessels.

spicuous.

C. A. YOUNG Secondly, as to opinions. The terms Exogen and Endogen,

Hanover, N.H., U.S., Sept. 13 as is pretty well known, were founded upon a mistake. A great deal ioo much has been made of the difference implied by them;

Arrangements have already been made for carrying out a in fact, if we compare a one-year-old dicotyledonous shoot with

similar suggestion to this by the Eclipse Committee ; and the a monocotyledonous stem, we find that it does not exist. If

corona will also be observed with an open slit.-ED. N. Prof. Williamson will look at the stem of the common artichoke, he will find it difficult to convince himself that he is examining Eclipse Photography and the Spectroscope an “exogenous” plant at all.

The endeavour of the Eclipse Committee to secure some The imagined characters which were implied by these terms uniformity in the photographs from different stations next are, nevertheless, as everyone knows, correlated with others, which in the aggregate enable phanerogamic plants to be divided into tended that immense

December does not appear to be duly appreciated, it being con.

personality” shown in various phototwo satisfactory groups ; but this is certainly not equally the case

graphers' manipulation must frustrate the good intention. I with the groups into which Prof. Williamson would divide the

submit that in this case the personality is greatly over-estimated ; vascular cryptogams. These groups, I think, most botanists will

that a number of competent photographers taking the same sub. agree in considering in the highest degree unnatural, inasmuch

ject would probably produce, under any ordinary circumstances, as, assuming the vegetative distinction upon which they are pictures bearing considerable resemblance; while by using like founded to exist, it is a wholly artificial ground for classificatory

apparatus and giving exposure of the sime duration, we might purposes. Nor is it any argument that one vegetative character safely predict a similarity of result amply sufficient for comparamust be good because others are in use, since the simple answer

tive purposes, and for the identification of structural peculiarity is that these coincide with natural divisions, while Prof. William.

should it exist. son's does not.

Among others there is a possible advantage to accrue from I shall not dispute Prof. Williamson's position that our living uniform work by the philosophers which I have not seen or Lycopodiaceæ should be interpreted by the more complete extinct heard noticed. Supposing the outer corona, rays, streamers, or types. To do this, however, the extinct types must be thoroughly

any portion of the apparently luminous matter be terrestrial, is it understood ; when we are dealing with imperfect material, com

unreasonable to expect that photographs, taken at stations more or parison with the more perfect but less highly developed existing less widely separated, will, when properly combined in the plants is not only justifiable but necessary. It is obvious that the great development of the stem in the stereoscope, give clear ocular proof of the sublunary situation of

such luminous matter?

HENRY DAVIS Lycopodiocese of the Coal Measures was correlated with their arborescent habit. I am inclined to think with Prof. William.

Ph ena of Contact son that the stem increased in thickness; it is certain that Lepi. dodendron was branched, and not improbably also Sigillaria. MR. STONE can safely be left to meet the arguments specially The branches as they were gradually developed must have been addressed to him in Prof. Newcomb's letter ; but as the subject the cause of an increasing strain upon the stem ; it seems to me relates to the only point of importance touched on in Prof. more congruous with known laws of the response of structure to

Newcomb's criticism of my chapter on the sun's distance, I crave circumstances, to conclude that the stem was proportionately de- permission to meet his general argument. veloped as the strain increased, than that the stem should have I submit that he tries to prove too much. been produced once for all of its maximum thickness without He admits that the phenomenon of irradiation exists in the case reference to the crown of branches that was finally to surmount it. of a disc. The sun's disc, then, must be to some extent enlarged,

I am quite prepared therefore to admit that the investing cylin- and the dark disc of Venus must be to some extent reduced by der may have increased by external additions, and probably did do the effects of irradiation. Now this being so, what becomes of the so; this would of course imply the existence of a cambium layer cusps, when Venus is all but wholly on the sun's disc? Either outside it. There is some analogy for this in the recent the irradiation is diminished near the cusps or it is not. If it is Isoëtes, where we have a “slight woody mass which occupies the diminished there must be distortion, because the disc of Venus longitudinal axis of the stem, but encloses no pith.+ Outside is then not uniformly reduced : is the irradiation is not diminished this we have a "bark-forming " cambium (which also adds, but a ligament must appear. more sparingly, to the wood mass); in Sigillaria and Lepidoden. Let any one draw a large circle (say a foot in diameter) on dron we might have had a cambium not merely renewing the paper, and a small one (say an inch in diameter) extending very bark but adding to the central axis.

slightly (say by the twentieth of an inch) beyond the boundary of In whatever way the increase took place, it was, as I think, the first; and let him blacken the smaller circle as well as all nothing more than an incident in the life history of a particular the space outside the larger one. He has then a space represent. race of plants, nothing more than an adjustment to an arborescent ing the disc of the sun with a very large Venus upon it near the habit dropped when the arborescent habit was lost, but showing

time of internal contact. Now let him conceive the whole of a lingering ancestral tendency in Isoëtes. Comparing a simple this space (a sort of exaggerated crescent) slightly enlarged as by stemmed palm with Dracana, we have a parallel instance of the irradiation, the enlargement-fringe extending outside the boundary strengthening of the stem pari passu with the continued deve. of the large disc and inside the boundary of the small black lopment of a system of branches ; only in Dracana it is the (incomplete) disc. He will find the conception of this enlargecircumferential part of the stem alone which developes.

ment exceedingly easy everywhere save near the cusps ; but here If I am right in regarding a stem gradually developing in size there is a difficulty in determining how the fringe outside the as the necessary correlate of a large system of branches, Prof. Wil. larger disc is to be joined on to the fringe inside the smaller disc. liamson's view practically amounts io the old division of plants It he can conceive these two fringes meeting in such sort as to into trees and herbs. I cannot see how it can afford any safe leave the reduced outline of the small disc completely circular up ground for a re-arrangement of the vascular cryptogams. to the very points in which it meets the enlarged outline of the

W. T. THISELTON DYER large disc, he will have done what Prof. Newcomb's theory re. London, Sept. 26

quires. But note, this must be done for the case when the fringe • Monthly Micro. Journ., 1869, P: 169.

of enlargement is wider than the twentieth of an inch, by + Hofmeister, Higher Cryptogamia, pp. 356, 361

which the small disc overlaps the large one. When this is the

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