Page images
PDF
EPUB

field of view, and passed out of it. The brightest portion of the streak, however, was brought into the middle of the field of view, where it occupied an excellent position (parallel to the refracting edges of the prisms) for viewing its prismatic spectrum. A slight effect of distortion (produced in the prisms) caused it to appear somewhat bent, like a bow, across the field of view. The spectrum presented the appearance of a narrow line of light, exceedingly brilliant, of a golden-yellow colour, and not more than 5' in width. It faded gradually along its whole length, and disappeared in about two and a half or three seconds. Its description, noted in the register, kept for the purpose at the time, was "neither double, triple, nor multiple, nor continuous, but purely and positively monochromatic."

"August 11th.-No. 8, 0h 15m A.M. Equal to a third-mag. star. Shot from B Cephei to & Draconis in three-quarters of a second, leaving a luminous streak for two seconds. The spectrum of the streak was a remarkably slender orange-yellow line of no appreciable breadth, without any continuous spectrum near to it, or any other neighbouring bands or lines. It was very bright, remaining in sight two seconds, and it gradually faded away until it vanished. The spectrum of the nucleus appeared to be undistinguishably the same as that of the streak.

"No. 9, 0h 20m A.M. Equal to a third-mag. star. Shot from a Cephei to 33 Cygni (Fl.) in three-quarters of a second, leaving a streak for one second and a half. The spectrum of the streak was dull grey, diffuse, about 10 in width, with a yellow line included in it on the side towards the red. The yellow line and the diffuse band disappeared together. The spectrum of the nucleus appeared to be appreciably the same as that of the streak.

"No. 10, 0h 33m A.M. Equal to a fourth-mag. star. Shot from p Cassiopeia to o Honorum in half a second, leaving no streak. The spectrum of the nucleus appeared to be concentrated into a few faint lines with wide intervals between them; but this description is very uncertain.

η

"No. 11, 0h 33m A.M. Equal to a third-mag. star. Returned about halfway along the course of the preceding meteor in half a second, leaving no streak. The spectrum of the nucleus was a concentrated point of yellow light, having all the appearance of an ordinary yellow shooting-star. "No. 12, 0h 42m A.M. Equal to Sirius; colour white. Shot from a Trianguli to n Piscium in one second and a quarter, leaving a streak for four seconds on its course. In the spectroscope the meteor slowly crossed the middle of the field of view, on a course directly parallel to the refracting edges of the prisms, producing a very superb spectrum. The spectrum of the nucleus was red, green, and blue, extremely brilliant. The train-spectrum was diffuse, 4° in width, in which a thin bright orange-yellow line was plainly seen on the side towards the red. The diffuse portion of the train-spectrum faded in about two seconds, apparently following the nucleus. The sodium line remained extremely bright for not less than two seconds longer, and faded gradually along its whole length, when it also disappeared. The singular characters of this spectrum were most distinctly and beautifully seen, and the long endurance of the sodium line, after the rest had disappeared, was leisurely watched.

10

"No. 13, 1h 23m A.M. Equal to a third-mag. star. Shot from P Camelopardi to a Draconis in half a second, leaving a streak for two seconds on its course. The train-spectrum was a diffuse band of greyish light 10 wide, somewhat brighter on the side towards the red, and it so vanished. The spectrum of the nucleus was appreciably the same as that of the streak.

"No, 14, 1h 55m A.M. Equal to a first mag. star. Shot from o Custodis to

3° below Polaris in three-quarters of a second, leaving a bright streak for three seconds. The meteor first appeared in the field of view, and passed out of it. The spectrum of the early portion of the streak, behind the nucleus, was a greyish diffuse band 4° in width. The spectrum of the nucleus was appreciably the same. The brightest part of the streak, before it faded, was brought into the field of view, well situated parallel to the edges of the prisms, and in the middle of the field for about two seconds. Its appearance was that of a golden-yellow line of light about 5° in length, some 4' in width, tapering gently towards the ends, and perfectly sharp and well defined. It was unaccompanied by any continuous spectrum, or any bands or other lines, and it so disappeared from the ends towards the centre.

"No. 15, 2h 15m A.M. Equal to a second-mag. star. Shot from u to a Andromeda in three-quarters of a second, leaving a streak for two seconds. The train-spectrum was a diffuse greyish-white band, 4° in width, and about 6° or 7° long, and faded away without any further change. The spectrum of the nucleus showed prismatic colours.

Shot from Cassio

"No. 16, 2h 16m A.M. Equal to a second-mag. star. peia to Andromeda in half a second, leaving a streak for two seconds and a half. The meteor was seen with the unassisted eye. The last-fading portion of the streak was examined in the spectroscope, where it appeared more widely diffused than when seen with the naked eye. Its colour in the spectroscope was a dull greyish white.

66

No. 17, 2h 27m A.M. Brighter than a first-mag. star. Shot from α Cassiopeia to o Honorum, leaving a streak for two seconds and a half. The train-spectrum was a diffuse greyish-white band 4° in width, not sensibly brighter in any part, and it so faded. The spectrum of the nucleus was bright red and green.

66

'Daylight at this time began to appear, and observations were obliged to be discontinued; the streaks of the August meteors might, however, already be plainly divided into two classes. In the majority of cases, a bright yellow line, having the unmistakeable appearance of the sodium line, was clearly visible in the spectrum. In a smaller number of cases the spectrum was merely a diffuse and greyish light band, or ordinary spectrum of weak intensity, resembling the spectrum of the glowworm's light. It will be interesting to observe this form of meteoric spectrum, should it be more common among the "phosphorescent" streaks of the November meteors than it was in August last, when only five such purely "phosphorescent" streaks were noticed entirely free from sodium light.

"The spectra of the meteor-nuclei were seen in a few cases only with distinctness, as they were in general overpowered by the brightness of the sodium light whenever that was present. When the streaks were phosphorescent only, and free from sodium light, the nuclei in general presented highly-coloured spectra, like the spectrum of solid matter at a glowing white heat, or like the spectrum of an ordinary gas-flame containing white-hot solid particles of carbon. A better night for observing nucleus-spectra would be the 12th of December, when meteors leaving no trains are plentiful; and they are for the most part very brilliant, radiating from some part of the constellation Gemini.

"That which spectral examination of the August meteors has most certainly brought to light is the existence of an extraordinary quantity of the vapour of sodium in their luminous streaks; so that many of the streaks, especially the most conspicuous and the most slowly-fading amongst them, consist of nothing else but soda-flames for a great proportion (that is to say, the latter 1866.

L

portion) of the time that they continue visible. Their condition is then exactly that of a flame of gas in a Bunsen's burner, freely charged with the vapour of burning sodium, or of the flame of a spirit-lamp newly trimmed and largely dosed with a supply of moistened salt.

"It is difficult to believe that the vapour of the metal sodium exists in such considerable quantities at the confines of the atmosphere. It is much more reasonable to suppose that it is brought into the atmosphere by the meteors themselves, so as to be deposited in the luminous trains that mark their course. The material of the August meteors is, therefore, probably a mineral substance in which sodium is one of the chemical ingredients. Such is the rather satisfactory termination of an experiment which it will be very easy to repeat whenever an abundance of meteors on the night of the 10th of August offers an equally favourable opportunity for examining their spectra by the aid of the meteor spectroscope.

"The connexion believed by adherents of Chladni to exist between shootingstars and aerolites is now shown, at least in August, to extend itself in some measure to their chemical composition. The meteorites of Aumale, which fell on the 25th of August 1865, were found, on analysis by M. Daubrée, to contain soluble salts (chloride and carbonate) of sodium. A circumstance so uncommon in the composition of aërolites, allies the meteorites of Aumale very closely with the sodium-bearing streaks of the meteors of the 10th of August. "In this manner, each new acquisition of knowledge, however unforeseen may be its origin, tends to support the theory of Chladni, and to confirm the belief that shower-meteors and shooting-stars are actually aërolites of small dimensions. In whatever manner aërolites and shooting-stars are related to each other in their astronomical and other peculiarities, they will evidently require a vast number of further experiments to unfold their real source.”

Report of the Committee appointed to Investigate the Alum Bay LeafBed. By W. STEPHEN MITCHELL, LL.B., F.G.S., Caius College, Cambridge.

THE bed known to geologists as the "Leaf-bed," or "Pipe-clay bed," of Alum Bay, is the band of white clay which occurs in the lower Bagshot beds in Alum Bay, about 200 feet from their base (No. 42 in Memoir of the Geological Survey). It is about 6 feet thick; but one portion only, a few inches in thickness, contains the plant-remains. No other organic remains whatever have been noticed.

The occurrence of these plant-remains was first observed by Mr. Prestwich (see Geol. Soc. Journ. 1847, p. 395), and since then collections have been made. Dr. P. de la Harpe, of Lausanne, examined these, and gave a notice of several species in a paper on the "Flore tertiaire de l'Angleterre," which appeared in the Bulletin de la Société Vaudoise des Sciences Naturelles for June 1856. In December 1860, in conjunction with Mr. J. W. Salter, F.G.S., he prepared the list which is published in the memoir of the Geological Survey of the Isle of Wight.

This list includes the collections from "the same strata worked at Bournemouth and Corfe Castle, in Purbeck, Dorset; " yet for the compilation of it

the total number of specimens that could then be brought together from the three localities was but about 300.

It is therefore no matter of surprise that in larger collections since made many fresh forms are met with.

At our last Meeting at Birmingham I exhibited drawings of some few of the most striking new forms, and mentioned that both Dr. P. de la Harpe and Dr. Oswald Heer urged the importance of a more careful examination of this flora.

A committee for this purpose was appointed, and the sum of £20 was placed at our disposal. Through the kindness of Professor Sedgwick and the Vice-Chancellor of the University of Cambridge, we obtained the services of Mr. H. Keeping, now at the Woodwardian Museum, who has had much experience in the working of this bed.

I went down to Alum Bay last September with Mr. Keeping, and remained there during the working to note the appearance of the leaves when first turned up.

In the majority of instances, not only the outline, but the venation, even the most delicate, is at first clearly visible, though a few hours' exposure to the air almost obliterates the more delicate marks. A washing with a solution of isinglass often preserves them; indeed in some instances it brings them out even more sharply; but, unfortunately, it often fails. There are some specimens on which I partly traced the venation with pencil as soon as they were exposed; now, after an interval of ten months, they are so faded that the part not pencilled is hardly, if at all, to be made out. It is much to be regretted that there is this difficulty in preserving the specimens, and we shall be very glad to receive suggestions for their treatment. All our specimens have had the usual isinglass wash, though I fancy it somewhat obscures the character of the surface of the leaves. I cannot speak with certainty on this point; for, as I had not anticipated such a result, I did not record the character of the surfaces among the notes I made on the spot. Still, from comparing the recollection I have of the appearance of the leaves when first turned up with their appearance now, I am almost certain this is the case. This I the more regret as the character of the surface of a leaf is often a useful help in determining its genus. I hope to have an opportunity of again examining this bed; and I shall endeavour to take both drawings and complete descriptions of the leaves before the air and light have in any way injured them.

After a fortnight, bad weather put a stop to our work. We had, however, succeeded in obtaining a good collection, numbering altogether some 470 specimens. The leaves are, on the whole, well preserved, but the bed in one part yielded forms so indistinctly marked as to be almost worthless.

I have in course of preparation descriptions of all the leaves in this, as well as in my own collection, which I will lay before one of the learned societies of London*.

Were they now complete, this would not be the suitable place for reading them; and the publication of them in a report, without drawings, would much lessen their value.

I have brought drawings of some of the leaves, which show that the aid afforded by this Association for examining this bed has helped us to obtain, not only finer specimens than Dr. P. de la Harpe and Mr. Salter had at their disposal, but also many fresh forms.

* The Palæontographical Society has undertaken the publication of a monograph.

I decline to attempt to fix the number of new species, or even genera, which we are able to add to the list in the Survey Memoir; for not only is the determination of fossil leaves at all times very unsatisfactory, but that list was not intended for a monograph, and has neither drawings (except a few) nor the exactness of description requisite for identification. Then, too, the nomenclature of fossil leaves is very unsettled, the same leaf having often half a dozen different names.

With regard to the species of fossil leaves, I believe the word "form" might often with advantage be used where "species" is now universally employed. "Species" is applicable only to the entire plant; "form" is applicable to individual leaves. When we consider the variation often met with in leaves growing on the same tree, I think we see reason for great caution in determining what "forms represent the existence of distinct species."

[ocr errors]
[ocr errors]

[Mr. Mitchell exhibited photographs and drawings of some of the larger and more interesting leaves].

Report of the Committee appointed to make Experiments on the differ ence between the Resistance of Water to Floating and to Immersed Bodies. The Committee consists of JOHN SCOTT RUSSELL, C.E., F.R.S.; JAMES R. NAPIER; Professor RANKINE, C.E., F.R.S.; and W. FROUDE.

THE following Report describes the experiments made by the Committee. The Committee held several meetings in the course of the winter and spring of 1864-65, and agreed to a programme of experiments, of which the following is a summary:—

"1. Two models to be made of painted wood, designated respectively as A and B.

"2. The models to be ship-shape, and each of them to consist of two equal and similar halves joined together at the middle water-line.

[blocks in formation]
« PreviousContinue »