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tion of a building with such elaborate and ornate internal culties have now, for the most part, however, been decorations for museum purposes. Now that the cases happily overcome. are nearly all in position and the specimens are gradually The Geological collections, in spite of their vastness being arranged in them, this incongruity between the have been to a great extent arranged. The Mammalian style and objects of the building becomes more and more and Reptilian Galleries are indeed almost completed, apparent. On the one hand, it is clear that the form, and much progress has been made with the Fish Gallery position, and illumination of the cases has in many and the several rooms devoted to the exhibition of the instances been sacrificed to a fear of interfering with the invertebrata and the stratigraphical collections.

The general architectural effect ; and on the other hand it is trustees have been fortunate in securing the services of equally manifest that it will be impossible to make full such an experienced palæontologist as Mr. Etheridge to use of the floor space, and especially the best-lighted por- second the energetic efforts of Dr. Woodward in this tion of it, without seriously detracting from the artistic department. By the insertion of drawings and tables, effects designed by the architect.

illustrative of the structure and classification of the fossil Thus we find the beautiful arcade formed by a series forms, the value of this part of the collection to students of pierced wall-cases in the Coral-gallery has its effect has been greatly enhanced. totally destroyed by the floor-cases, which it has been In the Mineralogical Gallery everyone must be struck found necessary to place along the central line ; and in by the improvement in the cases, now that the specimens the British gallery the vistas designed by the architect are no longer crowded together, as was the case in the have been completely marred by the insertion of large old museum. At the end of the general gallery, and in cases in some of the arches. Again and again we find the adjoining pavilion, there are a number of interesting massive columns, beautiful in themselves perhaps, break- special collections. First and foremost among these is ing up a line of cases, or throwing their contents into the unrivalled series of meteorites, which is now displayed deep shade. The peculiar tint of the terra-cotta, too, is to much greater advantage than at Bloomsbury; with far from being suitable for making the objects of the these are collections of crystals, both artificial and Museum stand out in relief, and this is particularly natural, of pseudomorphs and of rocks, or mineral aggremanifest in the case of the palæontological collections, gates—the latter being an entirely new feature in this where a great majority of the specimens have a very department. Large specimens, illustrating the abnormal similar colouring. When an attempt has been made to development, the mode of association, and the economic remedy this by giving the walls near the objects other uses of minerals are here being arranged, and they make tints ; it is found that such tints do not harmonize well a very fine display. Working mineralogists will be thankwith the general colouring of the building. Nor is the ful to Mr. Fletcher for his capital design of setting apart wisdom apparent of bringing into close proximity natural a case, in which new acquisitions to the collection are history objects with the conventional representations of exhibited for awhile, before being incoporated with the them adopted by architects. The crowding together, on general series. the same column or moulding, of representations on the The portion of the Botanical collection available for same scale of microscopic and gigantic organisms, of public exhibition is small, but Mr. Carruthers, the keeper, inbabitants of the sea and of the land, and of the forms has brought together a capital series of examples of all of life belonging to present and those of former periods the great divisions of the vegetable kingdom-illustrating of the earth's history, seems to be scarcely warrantable the dried specimens, where necessary, by drawings and in a building designed for educational purposes.

models. Greatly as we admire the spacious hall, ihe grand stair There are two points, however, in connection with the case, the long colonnades, and the picturesque colouring of establishment concerning which the readers of NATURE the whole building, we cannot but feel that the adoption of will naturally be especially desirous of information-first, such a semi-ecclesiastical style was a mistake. We fear that as to the facilities to be afforded to students for examinin the future there will be a perpetual conflict between the ing the valuable types and rare specimens in which the views of the keepers of the Museum-collections and those collections are so rich, and secondly, with respect to the of the architect of the building; for the erection of cases as improvements which are sought to be made in the they may be required in the most convenient and best Museum, regarded from the point of view of an educalighted situations cannot fail to detract from the striking tional institution. The surest test of the efficiency of the and pleasing effects of the architecture.

administration of such a museum as this will be found in Apart from this fundamental objection, however, we the manner in which these two great objects are attained find nothing but what is praiseworthy in the arrange-| by its keepers. ments which are being made to worthily exhibit to the Close days for students having been now entirely public these grand collections, of which such large portions abolished, the trustees of the Museum have provided have been long buried at Bloomsbury. In a few months galleries in each of the departments where scientific the whole of them will have been removed from their old workers can

pursue their studies undisturbed. We places of exhibition (or more often of sepulture) to the cannot help thinking that this plan is far better than new galleries, where the space available for their arrange the old one, which required original investigators to ment is so much greater. The cases in the Zoological attend on those days of the week when the public were Galleries are now almost completed and fitted, and the not admitted to the galleries—a restriction keenly felt by collections of osteology and shells with some of the busy men in this country, and more especially by stuffed animals, have been already removed to their new foreigners, who had perhaps come to this country with home-so that the public may hope to see the transfer of the sole object of devoting their time to the study of our the whole of the specimens completed by next spring. national collections. As there are valuable reference

The keepers of the geological, mineralogical, and libraries in each of the departments, and a general library botanical collections, which are housed in the eastern of scientific journals for the whole establishment, the stuwing and annexes of the building, have had a very diffi- dent has much greater facilities than formerly for carrying cult task to perform. They were called upon to remove on his work, and nothing can exceed the courtesy with these collections before the fitting of cases in the new which persons actually engaged in scientific research are buildings was completed, and in consequence of this the received and aided by the keepers and their assistants. re-arrangement of the specimens, with the incorporation The publication of the series of well-known and of the valuable material long packed away in the cellars valuable scientific catalogues is still proceeding. During at Bloomsbury owing to want of space, was rendered the pressure of work caused by the removal of these vast additionally laborious and troublesome. These diffi- collections, the trustees of the Museum have done wisely

serve

as

an

to avail themselves of the aid of specialists from outside, to it, written by Prof. Owen in his well-known clear and in connection with certain of the collections. Thus the attractive style, has been published. If the design is collection of the fossil foraminifera has been arranged by carried further, we hope the greatest care will be taken to Prof. T. Rupert Jones, whose catalogue of the same has make the classification and arrangeinent adopted in the been recently published. Dr. Hinde has in the same Index Museum harmonise with that employed in the way dealt with the grand collection of fossil sponges; and several galleries, for otherwise such a museum will not his illustrated catalogue of them is now in the press.

index to the great collection, but will But while the purely scientific objects of the Museumi be a source of confusion rather than of assistance to are not being lost sight of, we are glad to find that the students. greatest efforts are being directed by the keepers to the Of the zoological collections we can say little at predevelopment of the institution as a means of popular edu- sent. The birds will occupy the ground floor of the cation. In addition to the three admirable guides, pub- , western wing of the building, and the mammals the floor lished at the low price of one penny each, other popular above. The osteological collections belonging to these works in illustration of the collection are being prepared. two departments are already arranged in the upper floor, Thus Mr. Fletcher has written a penny guide to the and form a new and most valuable feature of the collection of meteorites, in which he has drawn up one of Museum. The articulated skeletons are exhibited on the best statements concerning the nature of these bodies, the floor and in glass cases, behind which cupboards are and of the grounds on which they are so greatly valued by constructed for the reception of unarticulated skeletons. scientific inquirers, that we ever remember to have read. The Pavilion contains a special series of bones, which are Simple in its language and mode of treatment of the reserved for purposes of study. The skeletons of whales subject, this little guide is replete with the most valuable are to be housed in the basement of the building. information-information which the student of the collec Generally we find that the convenience of the public has tion might ransack a library in vain to find.

been fully consulted in the arrangements of the building. S:ill more interesting is Dr. Woodward's venture in The lavatories and cloak-rooms are all that can be the same direction--an illustrated guide for the depart- desired, but we suspect that much disappointment will be ment of Geology and Palæontology. The woodcut illus- felt with regard to the refreshment department as at trations of this work are in part original, and in part present constituted. Small and inconvenient counters borrowed from various scientific manuals, the publishers are being erected on the highest story of the building, of which have generously granted the use of them to the outside the Botanical and Osteological Galleries respecMuseum authorities. By the aid of these woodcuts Dr. tively. The obstacle thus created to the ingress and Woodward is able to call attention to the chief facts con

egress of visitors to those departments, and the fact that cerning the structure of some of the most remarkable fossils

mice will infallibly be brought to them, is enough to in the collection, and the guide forms an excellent intro ensure condemnation of such a plan. We hope that the duction to the study of palæontology. At present the only trustees may yet reconsider the question, and find thempart of this guide which is illustrated by woodcuts is that selves able to devote to the purpose of refreshment, a which deals with the fossil vertebrates, for these only are room in the building which is centrally situated, and at as yet fully arranged; but in subsequent editions, no the same time entirely cut off from the collections. doubt, Dr. Woodward will give equal attention to the description of the most important forras, among the invertebrates. The design is an excellent one, and there

THE COMET is every promise in the present instalment of the work of its being admirably carried out. Such work cannot fail We take the following from the Sydney Morning Herald to be the means of diffusing in the widest possible manner

of September 19: accurate notions on the subject of natural history among Mr. H. C. Russell, Government Astronomer, sends us the people. We hope that its circulation may be as the following interesting particulars respecting the comet, large as that of Prof. Oliver's admirably illustrated guide under yesterday's date : 10 Kew Gardens, which we are glad to see has passed The comet discovered on the 7th has developed in through twenty-nine editions.

brilliance rapidly. When I first saw it on the 8th, the While on the subject of the means adopted by the nucleus was equal to a bright star of the second magniMuseum authorities to make the collections a means of tude; by the 11th it was brighter than a first magnitude diffusing correct ideas among the people, we cannot star, and I was able to see it for eight minutes after sunrise avoid referring to Prof. Owen's design of surrounding the on that day. Subsequently, the mornings were cloudy, great central hall of the building with an “Index and I could not see the comet either then or during the Museum." The idea is most praiseworthy, but its daylight, probably because of the sea haze, which is more execution will, we fear, be attended with serious diffi- or less part of the N.E. wind. The comet has, however, culties. Prof. Owen proposes to devote the first of the increased in brilliance so rapidly that Mr. Ellery was able six recesses on the western side of the central hall to the to see the comet at noon, and telegraphed to me to that illustration of man, the two next to the other mammalia, effect, and the air being clear it was found at once. I had the fourth to birds, the fifth to reptiles, and the sixth to not anticipated such a wonderful increase in its light, for fishes. On the other side three recesses are to be devoted now it is easily seen in the full glare of the sunshine, like to the invertebrata, and one each to botany, mineralogy, a star of the first magnitude, even when viewed without a and geology. Few naturalists will agree with Prof. Owen telescope, and it must be many times more brilliant than that the points which distinguish man from the rest of Venus when at maximum. In the large telescope the the animal kingdom, are to the zoologist, of such import- nucleus appears round and well defined, and measured ance as to necessitate the setting apart of a division of the three seconds in diameter ; from it, extended on each Index Museum for their illustration ; and the limited por- side, the first brarches of the coma, like two little cherub tion of the available space assigned to botany and wings, and in front, the great body of the coma, forming geology will occasion much surprise. As structural a brilliant and symmetrical head, and thence turning to alterations have interfered with the use of two of these form the tail six minutes long. Under close scrutiny it recesses, and the lighting of some of them is far from was evident that the coma had one or more dark bands, being satisfactory, the project may perhaps have to be curved like the outline, which made the form very integreatly modified. One of the recesses, that devoted to resting, but the glare of the sunlight made it very trying the birds, has been already arranged with instructive to the eyes. It is a splendid object, and it is to be rediagrams and well-selected specimens, and a penny guide ! gretted that no stars can be seen by means of which to fix

accurately the comet's position ; but should the weather fortunately, just before it reached the first transit wire it continue fine, it will be possible to do this with the transit was obscured by a passing cloud and remained so till just instrument. My observations this afternoon show that previously to its quitting the field, when it was still found the comet was moving away from the sun again, and to be bisected. I trust the Melbourne observers will not should this be maintained, it will become a morning, not fail to avail themselves of every opportunity to observe an evening object. At 1.15 p.m. to-day the comet was with the transit circle. If my memory serves me well I only 9m. 455. west from the centre of the sun, and 7m. of believe the history of astronomy does not furnish any declination south ; by 5 p.m. the distance in right ascen. previous instance of a comet being seen near the sion had increased three minutes; the declination was sun with the unassisted eye since the appearance of slightly less. Unless some rapid change in the direction the extraordinary and well-known comet of 1843. That of the motion takes place before to-morrow (and now that body was seen at 3h. 6m. p.m. at Portland, U.S., by a Mr. the comet is so near the sun this may result), the comet Clark, and consequently in full sunlight, and its distance will be seen without the aid of a telescope, about seven from the sun measured by him with an ordinary sextant. degrees west of the sun. History tells us of wonderful The present co.net was still plainly to be seen without the comets which outshone the sun; but it is usual to receive telescope at 5h. p.m. yesterday. To-day it will probably be these statements after liberal discount. Nevertheless the too nearly in a line with the sun to be seen ; but on Tuesday great comet of 1843 was easily seen by spectators when and Wednesday it will, I think, again be visible. In the it was only 1° 23' from the sun (that is, about half the dis- absence of any calculation I will here venture to offer one tance between the comet and sun to-day at i p.m.); and or two remarks. The comet appears, from a rough inspecat Parma the observers standing in the shade of a wall tion of its apparent path, to be moving in a track somesaw the comet with a tail four or five degrees in length. what resembling that which would be followed at this In Mexico, also, the comet was seen near the sun like a time of the year by the great comet of 1843 on its way to star of the first magnitude. It is probable, therefore, that perihelion, and it is a significant fact that the earth is the comet of 1843, the brightest of this century, was to-day almost exactly on the line of the comet's nodes, brighter than the present one.

and on the ascending side of the sun. At Greenwich We are indebted to Mr. John Tebbutt, of the Private mean noon to-day the longitude of the earth will be 3551", Observatory, Windsor, for the following communications while that of the ascending node of the great comet of respecting the comet :

1843 is about 358°. It will be remembered that at the September 16.-I succeeded in obtaining pretty good time of the appearance of the great comet of 1880 the observations of the comet on the mornings of the 9th and parabolic elements of that body were found to be almost joth instant, but since the latter date fog and cloud have precisely those of the great comet of 1843 (see my paper prevented observation. The following are the positions read before the Royal Society of New South Wales in secured :-September 8d. 17h. 54m. 525., R.A. =9h. 37m. July, 1880)—and it was therefore considered that the two 7'50s., Declination S. =0° 57' 46":4 ; September 9d. 17h. bodies were identical. It will be remembered, too, that 49m. 455., R.A. 9h. 45m. 47.815., Declination S. 0° 53' at a discussion at one of the Royal Astronomical Society's 36"-2. A third position will, of course be necessary for meetings it was suggested that although the period the approximate determination of the orbit. In the ab- between the returns of the co net in 1843 and 1880 was sence, however, of such a determination it may safely be 37 years, the time of revolution might be greatly stated that the comet is rapidly coming into conjunction shortened by the comet's passage through the sun's with the sun, and near its ascending node. It is not at coronal atmosphere. The question therefore arises—Is all improbable that the comet is passing between us and the appearance of the present comet a return of the same the sun, and that in consequence its tail will be pointed body? Should the comet make its appearance in the approximately towards the earth. As we do not at pre- west after sunset, it is quite certain that it cannot be sent know the exact apparent track of the stranger, it identical with that of 1843 and 1880; but if it should now would be advisable to watch the sun's disc at intervals rapidly revolve round the sun, and make its appearance during the next few days for a possible transit, and to again west of that luminary, it must certainly be a comet look out at night for any indications of the aurora conse- of very small perihelion distance. Whether it is the comet quent on a possible near approach of the earth to the of 1843 and 1880 time alone will decide. I dare say your tail. It will be remembered that our passage through the readers will call to mind the speculation of Mr. Proctor tail of the great comet of 1861 was marked by a general on the probable return of the comet of 1843 and 1880. exhibition of auroral phenomena. It is highly probable P.S. -At uh. 35m. a.m. to-day (September 18) I again that the comet will, towards the close of next week, be- detected the comet with the unassisted eye. It was then come an imposing object in the west during the evenings. about three-quarters of a degree west of the sun's westLike the recent Wells comet, this body will doubtless be ern limb, and apparently moving west. In this case the well observed with the transit circle in full sunlight. comet in a few days must be again looked for in the

September 18.-- The extraordinary interest which at- morning sky. taches to the comet now visible will, I trust, afford a The Herald writes :—The comet discovered on the 7th sufficient apology for my again trespassing so soon on instant has increased so greatly in brilliancy that it can your valuable space.

Supposing, from the rapid increase be discerned in daylight with the naked eye. The fact in the brilliancy of the comet that it would probably be was discovered by Mr. Ellery, Government Astronomer seen in full daylight, I turned my attention to the im- | in Melbourne, at noon, and by him co nmunicated to Mr. mediate neighbourhood of the sun about 10h. a.m. yester- Russell ; but the unusual phenomenon was observed by day. I at once found the comet without a telescope; it Mr. Tebbutt, of the private observatory, Windsor, at was visible about four or five degrees west of that about 10 o'clock. The authorities seem to agree that the luminary as a brilliant white dagger-like object. The history of astronomy does not furnish any previous head was beautifully distinct, and the tail could be instance of a comet being seen near the sun, as this is, readily traced for about twenty minutes of arc. I since the extraordinary and well-known visitant of 1843. succeeded in obtaining eleven absolute determina- It is probable, Mr. Russell states, that the comet may be tions of position with the equatorial, the approximate seen about seven degrees west of the sun, from which right ascension and declination of the last observation, luminary it is apparently, however, moving away ; and, uh. 25m. a.m., being respectively rıh. 22m. and 1° 10' should this movement be maintained, it will become a north. I attempted to observe with the transit instru- morning and not an evening object. ment. The comet entered the field of the telescope and So far the Sydney journal. was at once bisected by the declination wire; but, un- We are indebted to Sir H. Lefroy for an extract from

Earth.

h. m. S.

26 13:5

20
22

27 1786

9

...

- 28 14'2

...

...

the Eastern Star, published at Graham.stown, Cape found the length of the tail (northern branch) 25° on
Colony, in which Mr. L. A. Eddie, F.R.A.S, draws atten- September 22, and 22° on the following morning.
tion to the duplication of the nucleus which appears to By the kindness of the Astronomer Royal, we learn that
have been first remarked at the Royal Observatory, Cape the comet was observed on the meridian at Melbourne on
of Good Hope, on September 30, and on the same date September 15, 16, and 17 civil reckoning; equatorial
in the United States: a day or later European obser- observations commenced on the morning of September
vers very generally perceived it. On the morning of 10: Mr. John Tebbutt observed the comet the previous
September 24, at 4h. 3om., Mr. Eddie, says: “A most morning at his private observatory, Windsor, N.S.W.
glorious sight presented itself. The head of the comet The Melbourne meridian observations will be of great
had not yet risen, but a broad belt of golden light, about value in the determination of the elements of the orbit
two degrees in breadth, streamed upwards from the hori- prior to the comet's rush through the solar coronal
zon to about ten degrees; and from the northern margin region, the last one having been made only fifteen hours
of this again, a thin streak of less brilliant light extended before the perihelion passage.
upwards to about another twelve degrees, and when the Subjoined is an ephemeris of the comet for 18h. M.T.
head had fully risen above the horizon at 4h. 43m. a.m., at Greenwich. It will be seen that it is now well obser-
there were about twenty-five degrees in length of intensely vable on the meridian.
luminous matter, stretching upwards from a still more

Declination.
Fight Ascension.

Distance from luminous head, and inclined to the horizon at an angle of 70°. ... The head appeared as before, to consist of an

Nov. 16
9 25 58

25 3:1 1:496 1.688 apparently very solid though not very large nucleus, sur

18 9 21 25 25 39'0 rounded by a dense coma of no great extent, especially

9 16 40

1'500 ... 1°762 preceding the nucleus, and possessing no dark intervals,

9 II 43

26 46.4 &c.” The weather prevented further observation at

24
9 6 35

1510 ... 1.835 Grahamstown till the morning of October 3, when, on

26
I 16

27 46'9 directing his 9-inch Calver upon the nucleus, Mr. Eddie

28 ... 8 55 47

19514 1906 saw not one round planetary disc, as he had last seen it, The latest investigations on the motion of this comet but “two distinct ellipsoidal nuclei in juxtaposition, each

tend to indicate, contrary to the expectation that was at of them brighter on the interior edge, and drawn out, as

first entertained by many astronomers, that it is not it were, towards the comet's ulterior boundary, so that identical either with the great comet of 1843, nor with their conjugate axes were about double the transverse.

that which appeared with so great a resemblance in the They closely resembled, in the inverting telescope, the elements of the orbit in 1880. Calculations by Messrs. flames of two candles placed the one above the other, so Chandler, Wendell, and Hind, are so far in accord upon that the uppermost part of the lower flame almost over

this point. lapped the lower portion of the other. There was a dark rift the breadth of the transverse axes of these nuclei, extending from the hindermost one into the tail. These RECENT DYNAMO-ELECTRIC MACHINES

ELEGI

TLECTRICAL inventions of innumerable kinds have but the foremost was drawn, as it were, to the south, or of late followed one another with bewildering nearer to the direction in which the comet is moving.” rapidity; and the impetus to invention afforded by the Mr. Eddie further compares the two nuclei to the double

present development of electric lighting, and by recent star a Centauri when viewed through a clo'id with a low electrical exhibitions, is making itself felt in many ways. power. When daylight had advanced, they could be seen in Most important, perhaps, of these is the production of the telescope perfectly free from the light of the surround improved types of machines for generating electric curing coma. On the following morning the nuclei were distinctly divided with powers of 60 and 100 on the reflector:

Fig.1 the preceding nucleus was larger and brighter than the other, but both were, if anything, smaller than previously.

The Natal Mercury of October 6 describes the imposing spectacle which the comet presented as it rose apparently from the Indian Ocean. The nucleus shone with a brilliancy rivalling Sirius, or even Venus, and the tail was slightly curved, and though, as dawn approached, a litt diminished in length, appeared more concentrated and magnificent.

Observers who remember the great comet of 1843, as it presented itself in the southern hemisphere, are somewhat divided in opinion as to which body to give the

S palm on the score of brilliancy, though most of them appear inclined to favour the former. The Emperor of Brazil, who observed the comet of 1843 close to the sun on February 28, ani on the following evenings, considers it was not so remarkable for the brightness of the nucleus as the present comet, but that the tail had a much greater

Fig. 1.-Sir W. Thomson's Roller Dynamo. extent.

At Santiago, Chile, the comet was visible on September rents. Dynamo-electric machines, in fact, appear to be 17, some minutes before sunrise, and on the next undergoing the same kind of evolution which the steaminorning could be followed until 11h. 3om. with the engine has undergone; and just at present the tendency greatest facility without the telescope ; part of the tail appears to be in the direction of producing larger and near the nucleus was also visible, the northern border heavier machines than heretofore. being much brighter than the other. On September 20, The readers of NATURE will be familiar with the dethough the light of the comet had somewhat diminished, scription of Edison's large steam-dynamo, which first it was seen with the naked eye till 1oh. 30 n. M. Niesten, made its appearance in Paris in 1881, and of which two Chief of the Belgian expedition for the observation of examples are now at work in the Edison installation at the transit of Venus, observed the comet in Chile: he Holborn Viaduct. These monster dynamos, each requir

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ing from 120 to 150 horse-power to drive it, are capable which will probably be remedied by a rearrangement of of lighting from 1000 to 1300 incandescent electric lamps. the governors supplying the steam to the engines.

Six such machines have been also erected in New York New forms of dynamo-electric machine bave been to supply the central station of the Edison Light Com- designed by Sir William Thomson, some of these being

for direct currents, others for alternate, but all of them of Fig ..!

peculiar construction. The first of them, shown in Fig. 1, Fig.

may be described as a modification of Siemens' well-known machine, the drum-armature being, however, made up like a hollow barrel, of which BB is a sectional view, the sepa. rate staves

being copper conductors insulated from one B

another. They resemble the longitudinal bars used by Siemens in the armatures of his electro-plating machines, and by Edison in his steam-dynamo. At one end of the hollow drum these copper bars are united to each other in pairs, each to the one opposite it. At the other end their

prolongations serve as commutator bars. A similar mode of connecting to that adopted by Edison, is also possible. Inside this hollow drum armature is an internal stationary

electro-magnet, KM'K, whose poles face those of the Fig. 4

external field magnets. This internal magnet answers the purpose of intensifying the magnetic field, and making the magnetic system a “closed” one, as suggested long before by Lord Elphinstone and Mr. Vincent. This hollow armature Sir W. Thomson proposes to support on

external antifriction rollers A A' C c', the lower pair A A Fig. 5

being of non-conducting material, the upper pair being

made up of conical cups of copper split radially, and Figs. 2-5.-Sir W. Thomsyu's Disk-Dynarr.o

serving, instead of the usual commutator "brushes” to

lead away the current. The hollow armature may be pany. Here the unexpected difficulty has arisen that if driven either by the tangential force of one of the one of the machines drops in speed the currents from the bearing rollers, or by an axle fixed into the closed end other machines short-circuit themselves through the one, of it. and over power the steam-engine that is driving it; a fault Another machine devised by Sir W. Thomson, and illus

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Fig. 6.-Elevation of Gordon's Dynamo, showing the rotating coils. The “taking-off” coi's are shown in the top right hand corner. trated in Figs. 2, 3, 4, and 5, is a disk-dynamo for generating having upon its sides projecting wooden teeth, as shown alternate currents, and is therefore allied in certain aspects in Figs. 2 and 3, between which a wire or strip of copper to Mr. Gordon's machine, described below. The rotating is bent backwards and forwards, and finally carried to armature has no iron in it; it consists of a disk of wood | the axle B.

This disk is rotated between field-magnets

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