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ght ascension and declinations; the other nomenclature journey exceedingly well. My men are all with me, except twoasually adopted in cometary computations.

lest at Kuka.” This is the most important journey through the

Central Sudan and Sahara since the classical explorations of **$ 49°1 57°'I 30°:7 13806 127° -3 09643 296° -2 Barth and Rohlfs. 13 4607 538 29'1 1380 130*3098 36 302-3 73 397 56'0 212 1390 1436 09674

- -- - -- - -

297.8 27 6006 73.2 38.7 138.5 1071 0.8046 265:6

STROMBOLI IN 1891.1 643 33'2 138:1 1206 0:8839 , 2779 5*3 600 479 1387 99

10-9759 298:9 STROMBOLI is one of the most noted but least studied of 434 440 29'1 1384 130*7 09982 330-3 volcanoes. The regularity of the weak explosions which, 60'9 99'4 380 1387 79'1 0*5145 230-2 succeeding each other at intervals of a few minuies, characterize 28 4 290 186 1387 144'3 07495 19'2 its normal state, gives rise to the idea that its action is always 670 45.8 56:1 138.6 879 I '0028 3223 thus uniform and monotonous, and the occasional paroxysms to

532 109 6 317 138.7 64'0 03811 2150 which it is subject are apt to be overlooked. In reality the so47 674 234 72.9 1379 62.4 0.9872 330 8 called Strombolian phase of volcanic activity differs from the 23 5 501 3550 58.8 1387 63'1 08402 5 *7 | Plinian phase exhibited by Vesuvius and certain other volcanoes 140 374 285 28-7 138.5 1263 08046 119 merely by the absence of intervals of perfect repose between the

violent outbursts which are characteristic of the latter type. It is in this difference that the explanation of the fact is to be found,

that from time immemorial no explosion in any way comparable GEOGRAPHICAL NOTES.

to the great explosions of Vesuvius have occurred at Stromboli ;

for the ceaseless activity of the latter prevents the accumulation HE Royal Geographical Society has determined on a change of sufficient force to produce a powerful and destructive effect. le form and alteration in the title of its Proceedings, which | But from time to time the throat of the volcano does get more

materially enhance the value of the monthly publication. or less choked, and the efforts of the imprisoned vapour to : size of each part will be increased to ninety-six pages, and escape result in an eruptive phase of some violence. Such

volumes will be published in the year instead of one as for- | an event took place during the latter months of last year, and ris Internally the arrangement will be slightly altered, and the following description of the phenomena is based on the le the strictly geographical character of the publication will be observations of Profs. Ricco and Mercalli, and of Ing. ntained, the notes and record of geographical work from | Arcidiacono. er countries will be made at once more systematic and more The state of the volcano preceding this outburst had been one bular. A special feature will be the record of the “ Geo of relative calm for two years. In October, 1888, an explosion phical Literature" of the month, summarizing all the | had opened three new mouths on the upper edge of the Sciara. essions to the library, both books and memoirs. This will del Fuoco, from one of which lava was emitted. This was the m a subject-index to geographical literature, and serve as a commencement of a period of increased activity, with repeated atinuous appendix to the exhaustive subject-catalogue of the | issue of lava, lasting nine months till June, 1889. From this ciety's library which is now being compiled. The editorship date to the eruption of last year, and particularly during the six the new series remains in the hands of Mr. J. Scott Keltie, months just preceding, the activity was less than normal. It is e assistant secretary.

to be noticed, however, that there were two short intervals of WITH reference to the note on the death of Lieutenant

recrudescence, lasting only a few days, at the end of December,

1890, and January, 1891. hwatka, the Alaskan explorer, published last week, we are

On June 24, 1891, at 12.45 p.m., two strong earthquake ad to observe that an official enquiry negatived the theory of

shocks were felt over the whole island at an interval of a few icide, and showed that the fatal result followed from an over

seconds. Loud rumblings and a violent explosion followed use of morphia taken medicinally.

each. The : hocks were not confined to the island of Stromboli, THE German colonial authorities have recently come to a

| but were felt at Salina, a distance of 40 kilometres. Even the ry important decision as to the official spelling of the place

subterranean rumblings were heard at the latter island. The ames of their various protectorates in Africa and New Guinea.

first shock and the first explosion were, as might be expected, muropean names are to retain their ordinary form, but all native

more violent than any which succeeded. Windows were mes are to be rendered phonetically according to a new set of broken at the semaphore station, and a great precipice of rock les. These rules so closely resemble those put forward by the

fell into the sea ai the Filo del Cane, and other rocks in the oyal Geographical Society, and now widely used, that it ap same locality were so loosened that they sell on following days. ears possible ivy some slight concessions on both sides to make

Two powerful columns of ash, like thick smoke, arose from the ne set serve both for English and German. The letters c, 9, x,

crater and ascended far above the summit of the island. Great ad : are dispensed with as redundant, c and 2 being rendered

masses of scoria were ejected and sell toward the northern part ts, r by ks, and g by kw. The gutteral ch becomes kh, the

of the island, burning the grass and fig-trees. A boat passing nglish ch being given as ish, and the sound of the English j as

to the north-east of the island at the time of the first explosion The German ; sound will be represented by y, and the

could not see the semaphore signals, owing to the quantity of tlet ; used only for the French sound, which is represented in

ash in the atmosphere. Lapilli fell around the eruptive mouths nglish as sh. The German sound of w is rendered as v, the

for a radius of a kilometre and a half, and a fine, dark grey ash ter w being kept for the English sound. Unfortunately the rained over the whole island. A stream of lava issued from a ter s is kept for its soft German sound, the sharp sound of the

point on the Sciara del Fuoco near to the most western mouth,

point on the nglish letter being shown by s. The use of the English : ! and a deep fissure formed its upper rim nearly in the same Ruld have overcome this difficulty and removed the most serious place as that of November, 1882. For two days the lava con nacle to a common orthography.

tinued to flow, and loud explosions were frequent. The rumb

lings were almost continuous. On the 26th the emission of ash CAPTAIN MONTeil, whose arrival at Kano on his way to

ceased, but moderately vigorous outbursts occurred with the ake Chad was referred to in May last (vol. xlvi. p. 110), has | ejection of incandescent scoria till the 27th ; but on the 28th

last been heard of, and his mission, although involving two and 29th the volcano had resumed its wonted calm. On the Fars of travel in the Sudan and Sahara, appears to be success 3oth, however, a fresh earthquake, accompanied by rumblings ally completed. The facts could not be put more concisely than and a violent explosion, showed that the volcanic forces were

Monteil's official lelegram to the French Foreign Office, which not yet spent. An immense column of vapour and incandescent rrived on November 15:-"October 17. To-day I entered materials arose from a new breach on the edge of the Sciara, ne territory of Ferzan by way of Tejerri coming from while an abundant current of lava flowed down the slope reachuka. Having set out from Kano on February 19, ing the sea at its foot. The whole of the powerful explosions reached Kuka on April 10, where the reception was

o the 30th were repeated at short intervals, but the activity acellent. I left Kuka on August 15 with a guide, sent by ne Sheikh to accompany me to Murzuk .... which I expect

| Sopra il Periodo eruttivo dello Stromboli cominciato il 24 giugno, 1891.

Relazni ne dei Prof. A. Ricco e G. Mercalli col Append.ce dell' Ingegnere reach on or about the 25th, and to stay there just long enough Arcidiacono ("* Annali dell' Ufficio Centrali Meteorologico e Geodinamico arrange my departure for Tripoli. Badaire has borne the [2] XI. Pt. 3, 1892)

gradually declined till July 4, when its normal state was June-July), sell over the island, covering the ground in som reached. The eruptions were again violent, with emission of places to a depih of several centimetres. On the evening.' lava from the 16th to the 23rd of July.

September i dense columns of ash were again emitted, ance The mouths on the edge of the Sciara, which were contem the afternoon of September 3 the whole crater was envelope poraneously active during the above period, were four in num in a thick mantle of steam, in the midst of which could be die ber-two at the northern end and two at the western end. One | seen a reddish-grey column of ash rising with extraordica of the former pair was opened by the explosion of June 30, and violence to a great height, when it spread out into a volar from it was ejected the greater part of the detrital material of | “pine.” A Iresh stream of lava was also observed. Eruption the eruption, so that around it a cone has been built up, trun. | succeeded each other at short intervals, accompanied by c: cated by a crater, sub-elliptic in form, of about 60 metres in tinuous rumblings, interrupted now and again by loud er maximum diameter. The height of this new cone above the old sions, like heavy artillery. As far as could be observed, on the edge of the Sciara is about 50 metres. The other crater is western side of the crater was a single mouth of almost circa situated on the deep fissure mentioned above, and at night, from form, 10 metres in diameter, which was most active in sepia: the sea the incandescent lava could be seen in free communica | up vast columns of ash and projectiles of all kinds. To the es tion with the atmosphere-a circumstance which explains the | could be seen one or more little mouths, which tranqs.. fact that the explosions from this crater were rare and of feeble 1 emitted large volumes of steam, while in the midst a lar? intensity. The two western ones were situated one below the | aperture, 30 metres in diameter, irregular in form and deta other with an interval of about 30 metres. Near the lowest, three fissured, was in powerful action. The activity, however, grad large sumaroles gave forth dense columns of steam, while other ally quieted down, and towards the end of the year the lesser fumaroles were plentifully scattered about. The majority volcano resumed its normal state. of the explosions took place from these two mouths. During In conclusion, it is useful to compare this eruptive phase : this same period, lava was emitted three times, (1) on June 24, Stromboli with other contemporaneous seismo-volcanic soon after the first two explosions from the most western part nomena of the Italian peninsula. It appears that earthquas of the Sciara ; (2) on June 30, from the crater on the fissure ; occurred in various districts in the early months of is (3) on July 16, from the central part of the Sciara, between the especially one on June 7 in the Verona district, rather severe, first two. They all reached the sea, and since the second stream casioning loss of life. Vesuvius was rather more active the doubled itself round an obstacle about half way in its course, usual during the whole of June, and in correspondence with four new points were formed on the shore. The thickness of the great sumarole of the solfatara at Pozzuoli, increased in ter the lava at these points varied from 4 to 6 metres. Specimens perature. It is particularly interesting to note that Vulcan.. of the lava collected from the most western stream showed that the other active volcano of the Lipari Islands, remained in pe it consisted of an almost homogeneous blackish brown paste, | fect calm during the whole period, emitting only vapoar tror compact in the interior, but becoming more and more porous the sumaroles. As, however, the character of the eruptions : and reddish in colour towards the exterior. Some of the larger the lithological composition of the material ejected from a cavities were internally covered with a shining brown patina, | volcano differ so greatly from those of Stromboli, it is tolerabig Externally it was covered with a rough crust, reddish-brown in certain that there is no free and direct communication betwest colour, and of scoriaceous aspect. It was sensibly attracted by the reservoirs of these two volcanoes. In lact, Stromboli pre the magnet, and melted without effervescence to a brownish- | sents a much greater analogy with Etna The similarity of the green glass. Crystals of plagioclase, augite and olivine were | lithological composition of the lavas of these two volcanoes a apparent. In section, about two-thirds was rendered opaque already been referred to, and, further, Prof. Mercalli obser: and black by very minute microlitic granules of magnetite which that the last four or five eruptions of Etna have all been ines were intimately mixed with a transparent glassy base, colourless diately preceded or followed by a paroxysm at Stromboli. 2 or inclining to greenish. The remaining third consisted of a is thus possible that there is a real relation between them. great number of colourless transparent microlites of plagioclase.

L. W. FULCHEL Fluidal structure was only just apparent. In this microlitic paste were scattered crystals of plagioclase, augite, and olivine. The augites were greenish in section and possessed a feeble pleochroism. The olivines were corroded and irregularly frac

A LARGE METEORITE FROM WESTERN tured,

AUSTRALIA. Analysis gave the following numbers :-

IN the Mineralogical Magazine and Journal of the Nike Etna.

logical Society of July, 1887 (vol. vii.) Mr. L. Fletche Mean of analyses of Stromboli.

M.A., F.R.S., president of the Society, describes four spe:

20 mcdern lavas. Silica ... ... 50°71

49'45

mens of a new meteoric iron found at Youndegin in Wester Alumina ... 13.99

19:30

Australia. They were discovered about three-quarters of a pl Ferric oxide 513

to the north-west from the top of Penkarring Rock, in the aber

{ 11.82 Ferrous oxide 9'10

district, about seventy miles from York. These fragments va Manganous oxide 42

found by Alfred Eaton, a mounted police constable, who ! Lime ... ... 10 81

10-21

duty in ihe district of Youndegin, when he brought in one of Magnesia ... 4.00

3.69

sour pieces he found on January 5, 1884. Mr. Fletcher 6 Potash . 3'02

that the late Mr. Edward T. Hardman, F.G.S., the Soda . ... 2 87

3:58

Government geologist, expressed his belief in the meteoric orig Loss on ignition '24

of these iron masses. Later the above-named Alfred Eaton s Cl and SO, (traces)

sent with a native assistant with instructions to bring in a

other three pieces, and at the same time an unsuccessful ser 100-35 99-38

was made for additional fragments. In the above accoun:

stated that the sour pieces were lying loose on the surface, The lava is similar to other lavas of Stromboli, and to show of them close together, and the fourth fifteen feet away. 2 the great similarity between the lavas of Stromboli and Eina, weighed respectively 25% lbs., 24 lbs., 174 lbs., and 6 lbs.. the mean of the numbers of twenty analyses of modern Etna largest and smallest fragments are now in the British Me lavas is appended for comparison.

collection, and the specimen of 24 lbs. is in the Geology The scoria, lapilli, and ash of the eruption present no special Museum at Freemantle, and the fourth piece, weighing 1701 features, but are what might be expected from a lava of the was presented to the Melbourne Museum in Victoria above composition.

The new specimen now in my possession was discovered Although the volcano had reached a state of comparative year, and weighs 382} lbs., and measures 224 inches ! calm at the end of July, this did not last for very long. Towards 201 inches wide, and 134 inches in its greatest Thickness! the end of August fresh signs of activity gave warning of an form it is roughly convex on one side and concave on the approaching explosion, which took place on August 31. It on both sides of which are large depressions or pittings sin! was preceded by an earthquake a few seconds before, and as a | to those usually observed on other large masses of meteoricei result a vast column of ash rose above the volcano, while scoria | It is somewhat triangular in outline, but with irregular 3 and other projectiles were shot out to a considerable distance. It has one small hole quite through the mass near the top, Soon after, a fine ash, dark red in colour (instead of black as in numerous deep holes, one near the bottom left-hand and

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having a diameter of about if inches and 4 inches deep; another | detach a fragment of which the cut face was not 24 inches at the opposite bottom corner 2 inches deep and 2 inches in

square. liameter; also another of 3 inches deep, and several others. Mr. Fletcher also states that on treating a specimen of On the upper edge especially, and at several other parts near, this Youndegin iron to the action of bromine water, or of also on the edges, are fractured surfaces, as if in its fall a miss dilute nitric acid, the polished section gave no definite or masses were broken off, leaving a coarse crystalline structure, figures, but assumed a damascened appearance very like the and which would indicate that several other large holes having i Tucuman iron and of that of Brazos, being very similar to existed before its fall on the earth, probably all or most of the the latter in the proportion and distribution of the Schreipieces were connected together, and might have fallen in one bersite ; some specimens of the Arva, the Sarepta, and the nass. It would be interesting to know if any of the pieces recently found Canon Diablo are similar as exhibiting these ilted together at the fractured surfaces as seems to me might be characters.

[graphic][merged small]

»ssible. I observe that the two specimens of this iron in the
ritish Museum collection exhibit similar fractures on the edges.
efore receiving this specimen I was informed that two masses
ere found, but have no information at present as to the size
d weight of the other.
Mr. Fletcher in his paper minutely describes the size and
rm of the two British Museum specimens, and that the specific
antity was determined from three small pieces from the larger
ecimen, and gave 7:86, 7:85, and 7'72. He also states that a
rtion was cut off the larger piece by means of hack-saws, and
is found to be so hard that three weeks were required to

The Youndegin iron was also remarkable in containing the minute cubic and modified cubic crystals, having metallic lustre and of a greyish black colour, and which were determined to be graphitic in character, but of a diamond-like form ; but were later found to be still distinct from the diamond, but having somewhat more the features of graphite. Mr. Fletcher therefore decided to give the name of Cliftonite to this substance, as being a new form of a carbon mineral. A most exhaustive description of this new mineral is given in his paper. Similar crystals of this substance are found in one or two other meteoric irons.

The composition of the Youndegin iron was found to be as į are concerned all bodies may be arranged in two gror follows:

according as their colours change or do not change in tins Iron ...

92.67

their angular relationship to the light varies. Nor is the Nickel

6:46

classification entirely an artificial one, since, as will shortly be Cobalt

0:55

seen, though this change in tint with variation in the liez Copper

trace

source is an essential difference, it is not the only differcie Magnesium ...

0:42

even in the colour manifestations of the two groups, for is Phosphorus ...

O24

also characteristic of the nature of the colour producing strucat Sulphur ... ... none

It is to the above-Dienioned varying colours that we apply the Insoluble cubes

0'04

term iridescent, from the resenıblance they bave in the reglene

or play of colours to the tints of the rainbow. The unvan 100-38

group of colours, baving no equivalent term to "iridescence"

express the nature of their colour production, are spoken : JAMES R. GREGORY.

as" pigmentary," or absorption colours. In naming examps of objects, natural and artificial, grouped as above in accordas:

with the nature of their colours, it is difficult to make a selected THE CROSS-STRIPING OF MUSCLE. where all are so varied and characteristic. I have preferre

therefore to cite only such instances as I myself possess, z PROF. RICHARD EWALD of Strassburg, has just com

am therefore able to show you. As examples of pigmenta municated a paper to the fifty-second volume of the Archiv. colours, I need only name one or two for the sake of comparisc. f. d. ges. Physiol., in which he confirms Prof. Haycraft's views since the colours of most objects ordinarily mel with are o concerning ihe structure of striped muscle. The latter ob mentary. Leaves, Powers, dyes, birds, fish, insects, minerze, server has held for many years that muscle fibrils are varicose &c., exhibit these colours, some ala ost entirely, and 2. threads, and that the cross-striping is but an optical appearance excepting fish, in far the majority of instances. Os objet due to this varicosity. The varicosity is often difficult tv den. on displaying iridescent colours we have also examples in the strate in the ordinary way, and most histologists were not pre- various divisions of the animal, vegetable, and miser: pared to admit that the stripings are all and entirely due to it. kingdoms. Amongst birds the most striking examples * Prof. Haycraft, however, recently brought forward to the Royal | found amongst the humming birds, sun birds, birds Society of London, and to the Berlin International Medical paradise. &c. Insects. again, furnish numerous example, Congress, fresh and striking proof of the strength of his position, | more especially amongst tropical species, though not, perhe by demonstrating films of moist collodion, on which pieces of proportionally in greater numbers than amongst those belong muscle had been pressed and then withdrawn. As a result of

| to our own more temperate regions. The colours of fish this pressure the collodion films were stamped as with a seal, almost entirely iridescent, since their very whiteness, or silver and the impressions revealed in striking detail every stripe of sheen, is due to the admixture of the iridescent colours the original fibre. Prof. Ewald confirms these experiments in innumera' le minute thin lamellæ, too small to be seen individ the fullest manner, but suggests that the collodion impressions ally with the naked eye, but plainly perceptible under te might be produced on the assumption that there are layers of

microscope. In the vegetable kingdom iridescent colours hard and soft material alternating with each other in the course far more numerous than is ordinarily recognized, sod of the fibrils. In this case the hard material would press into the surfaces of the cell walls produce interference colours whid the collodion and make a series of furrows, which would appear are more or less obscured by the pigmentary colours of lease as a series of stripes when examined with the microscope. Prof.

and coloured flowers, but may be readily seen in the case ! Haycraft had previously demonstrated the varicosity of the fibrils, white flowers by the aid of a lens and sunlight. Under the seen by transmitted light, and had published photographs of his conditions each cell may be seen to sparkle with its can preparations, but Prof. Ewald was still sceptical upon this par iridescent colour, forming, by admixture of the intersereta ticular point, and sought to assure himselfstill more conclusively. tints of neighbouring cells, the varying shades of white seen With this end in view be examined muscle, which had been numerous flowers which are devoid of pigmentary code rendered quite opaque, by means of reflected light, for under Mineral bodies displaying iridescent colours are also numerot these circumstances the influence of the internal structure would opals, sunstone, fire-marble, felspar, mica films, tarnish be entirely set on one side, and the surface of the fibrils would various metallic crystals, certain crystals of chlorate of pots alone receive and reflect the illuminating rays. For purposes of &c., are examples. illumination Prof. Ewald used the apparatus of W. and H. In describing the various natural objects for purposes ! Seibert, of Wetzler, by means of which vertical rays can be identification, or mere description, no account can be consider! projected upon an opaque object; and he rendered his prepar complete which omits ail reference to their colours, and EN ations, both of fresh and of hardened muscle, quite opaque by a especially is this the case where the colours constitate sad method of over-silvering. Under these conditions Prof. E ald striking feature, as in the case of iridescent bodies. In inou found that the cross-striping is most distinct, and he was able, erable instances, more especially amongst birds and insed with his admirable method of illumination, to examine the sur their specific names are taken from some conspicuous ood face of a muscle just as one may observe the surface of the they possess. It thus becomes evident that a correci deca country at night by means of a search-light from an observatory. I tion of the colours of bodies is of importance, and where tid With the light persecıly vertical the tops of the ridges of the colours are of the pig uentary, or unchanging kind, this i muscle are bright, and the valleys on either side in half-light. matter of no difficul y. How different, however, in the By shifting the light to one side or to another the slopes of the of objects, the colours of which not only vary with every che ridges can be thrown alternately into shadow or bright ligbt. of position, but disappear altogether, unless viewed with spec Prof. Ewald concludes by admitting that his experiments fully relation to the light source. Nor can it be wondered at th prove that the striping is due to the shape of the fibrils alone, descriptions of these objects, even by observers of undout and that the internal structure of the muscle plays no part in its repute, vary according to the different angles from which 'N production.

have been viewed ; or are vague and profuse, owing to frus attempts to describe their changing tints produced by ered

movement. The fact is, no words can convey an ades! IRIDESCENT COLOURS.1

impression of the gorgeous effects pr duced by most of

objects, whether birds, insects, or fish, when in motion o n taking a general survey of coloured objects, whether brilliant sunshine. Some notion of the difficulties to cons

natural or artificial, we become aware of the fact that with in describing the colours of humming birds, for exa whilst the colours of some remain unchanged as regards tint, may be gathered from the remarks of Wallace in his work whatever their position in relation to the incident light, the “ Tropical Nature," when speaking of humming birds :tint of others varies with every alteration in their relationship some species they must be looked at from above, in others -1 to such light source. We thus see that so far as their colours below; in some from the front, in others from behind, ia s

to catch the full glow of the metallic lustre ; hence, when I 1 By Alex. Hodgkinson, M.B., B.Sc. Reprinted from the fifth volume of the

birds are seen in their native haunts, the colours come ad fourth series of " Memoirs and Proceedings of the Manchester Literary and Philosophical Society." Session 1891-92.

and change with their motion, so as to produce a stariling

eautiful effect.” Most observers, in describing the colours of trouble of measuring angles is avoided, since we know that the idescent bodies, do so by attempting to depict the varied incidence is perpendicular when it coincides with reflection. fects produced by casually changing the position of Now, the reflected light may be made to coincide with the le object in relation to the light, omitting to mention the inciden: light by reflecting it on to the object by means of a cact sequence of the play of colours, or the relation of these mirror, and so adjusting the object that the light reflected from blours to the direction of the iridescent light, i.e., whether pro- it passes to the eye through a perforation in the mirror. When aced by perpendicular or oblique illumination. Here is a l examined in this way iridescent objects are marvellously altered escription of the tufted neck humming bird, Trochilus ornatus, in appearance, their changing colours are replaced by one fixed ken haphazard from a well-known work :-" The throat is of tint, visible only in one position, a fact which serves at once fine green colour, variable in different lights to a golden hue to distinguish them from bodies coloured by absorption, which ith a yellow or brown metallic lustre, and below that the remain coloured whatever the relation to the incident light. hole of the belly is a rich brown, glossed with green, and Such methods of examining bodies scarcely takes more time Iden." Sucb descriptions as the above, which happen to be than by the eye alone. The mirror may be attached to a e first I met with in seeking for an instance, are vague, and spectacle frame so as to leave both hands free, such as the one il to give a definite idea of the appearance of the object. But I show, or may be a simple hand mirror. For objects too gueness in the description of these objects is not the only small to be seen by the unaided eye, I have so arranged the sult of the changing character of their colours. As might micr scope that light is made to pass down the tube of the instru• expected, where such variation in appearance exists, the ment, through the object glass on to the objects, and by a escriptions of different authors are alınost as variable as the special arrangement, so adjusted the position of the object that

lours. Few attempt descriptions without acknowledging the light is reflected back again through the instrument to the le hopelessness of the task. Thus Jardine, after describing eye. The method is thus available for macroscopic as well as his humming bird, Chryslampis mosquitus, remarks :-" It is microscopic objects. npossible to convey by words the idea of these tints, and To illustrate the practical value of this plan of examination, aving mentioned those substances to which they approach I have here a few objects exhibiting iridescent colours, which, earest, imagination must be left to conceive the rest.” And I by trial, will be found to give the following results :iduce this quotation as fairly expressing the feeling of The crest of this humming bird, Chrysolampis mosquitus, aturalists in reference to the description of iridescent objects which, to the unaided eye, appears resplendent with all shades enerally. Recognizing the admitted inability of observers to of red, orange, yellow, or green, according to the angle of onvey by description an idea of the appearance of these iri- the incident light, appears, when examined by the mirror, of escent objects, and having myself, for many years, constantly one unvarying red tint, disappearing when the object is moved (perienced the same difficulıy, I have been led to adopt a but absolutely unchanging in tint. Such an object, therefore, ethod for the examination of such objects, which, whilst I should describe as “iridescent red”; all else regarding its tremely simple and available in its application, yields unvarying colour may be inferred. Again, the breast, or gorget, of the sults with different ob ervers, results, moreover, which admit same bird reflects all shades of orange, yellow, or green to the the simplest description.

eye alone ; with the mirror it is seen of a deep orange, which, Before describing this method, I may say that long experience as before, is unchanged in tints by any variation in position. the examination of iridescent objects has proved to me that, Such an object I would describe as “iridescent orange." The most without exception, the colours of natural iridescent gorget of another humming bird, Calliphlox amethystina, to the ojects are due to interference produced by thin plates. In eye alone appears crimson, orange, yellow, or green : with the der, therefore, to render clear the principles on which the mirror it is iridescent crimson only, spectroscopically a red of ethod I propose is founded, I will briefly refer to certain sun the 2nd order. Amongst insects, instances of iridescent species imental facts in connection with colour production by thin are numberless, the results of examination are just the same as ates, and for this purpose will select a thin film of mica, which in other iridescent bodies. This butterfly, Morpho, to the eye ith light at perpendicular incidence, appears red, iridescent alone appears either greenish-blue, blue, or violet, as its d. If, now, this plate be inclined so that the light falls on inclination to the light varies ; examined with the mirror it at a more oblique angle, it is, of course, reflected at the same appears green, and should be described as iridescent green, or igle, and now appears orange, and if the plate be still further iridescent bluish-green. This beetle, Foropleura bacca, appears clined, the reflected light appears yellow, then yellowish any shade of red, yellow, or green to the eye alone ; with the een, green, and bluish green, and if the light were not too mirror only iridescent red. In this extraordinary beetle, piously reflected from the first surface to allow of perceptible Chrysochroa fulminans, we have all the colours of the spectrum terference by further inclination of the plate, all the colours in their natural sequence, beginning with red at the tip of the

the spectrum in their proper sequence might be observed. wing case, and ending with violet higher up the elytron. These ve same results, but much more vividly, may be seen in these colours vary in an indescribable manner when attentively ystals of chlorate of potash. Thus, we see that by rendering examined at different angles of incident light with the eye - incident light more and more oblique, the reflected light alone ; with the mirror the wing cases are seen to be coloured anges from a lower to a higher tint, that is, froin the red successively from base to tip iridescent green, yellow, orange, vards the violet end of the spectrum. And this is what and red, and these tints remain unaltered by change of position urs in the case of all iridescent bodies, as the incident of the object. This piece of Haliotis shell exhibits indescribaht becomes more oblique the colour changes to the tint above ble changes of colour with every movement, but the difficulty in the spectral order, so that, if we know what colour any of description, though by no means removed, is immeasurably h object appears when seen at a certain angle, we can inser lessened by the use of the mirror. And the same with this at colour it will change to on varying the incidence. This specimen of iridescent iron ore, its colours, which vary to the untle (Sagra purpurea), for instance, is red at perpendicular aided eye, remain unchanged when examined by the mirror. dence, it will, therefore, appear orange yellow and green To simplify the description of iridescent objects, therefore, I en examined by successively increased obliquity of light. I would advocate the above method, and would describe the

the same is true of all other iridescent red objects. If result of such examination by recording the colour observed object at perpendicular incidence be green, as in the case by aid of the mirror, and prefixing the term “iridescent" to his beetle (Buprislis), it will become blue and then violet express the changing properties of the colour. Bearing in be incidence is increased. We thus see that an iridescent i mind the unvarying nature of these changes, a far clearer idea

ct varies in colour, simply because it is examined by light may be formed of the appearance of these objects than from dent, and therefore reflected, at different angles. Thus, any attempted description of what is admittedly indescribable. rent observers see the same iridescent object of a different Time and space are also economized by the omission of lengthy ur, when they view it illuminated by light at a different descriptions. The accuracy, and, therefore, the value of any e of incidence. If, however, the object is seen by all at description of colour, is always enhanced by mapping its specjame angle of the incident light it will present the same trum ; more especially is this true in the case of iridescent ur, and this is, in fact, what the method I propose ensures, colours. This is easily done, and by applying such map to a

that iridescent objects shall always be seen by light at one spectral chart, the order of the colour, and iherefore its tint, is the same angle of incidence. The angle I select is one of apparent. In examining many objects, chiefly birds or insects, o that the incidence and reflection are normal or perpen. by means of the mirror as above described, apparent exceptions lar to the reflecting surface. By selecting this angle all are repeatedly met with to the fact stated above, that the colour

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