Observations of Deflection and Vibration for absolute measure of H. F.

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III. "On the Fossil Mammals of Australia.-Part III. Diprotodon australis, Owen." By Prof. OWEN, F.R.S. &c. Received December 10, 1869.

(Abstract.)

In this paper the author communicates descriptions, with figures of the fossil remains at his command, of Diprotodon australis, which have been received from various localities in Australia, since the first announcement of the genus, founded on a fragment of the lower jaw and tusk, described and figured in the Appendix' to Sir Thos. Mitchell's Three Expeditions into the Interior of Eastern Australia,' 8vo, 1838.

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The fossils in question include the entire cranium and lower jaw with most of the teeth, showing the dental formula of :—i. C. m.5=28; portions of jaws and teeth exemplifying characteristics of age and sex; many bones of the trunk and extremities.

After some introductory remarks, the author proceeds to the description of the skull and teeth, which are illustrated by many figures, those of the teeth being of the natural size. The result of the comparisons detailed establishes the marsupial character of Diprotodon, and the combination of characters of Macropus and Phascolomys with special modifications of its own. These latter are more fully and strongly manifested in the bones of the trunk and limbs, subsequently described. The pelvis and femora present resemblances to those in Proboscidea, not hitherto observed in any other remains of large extinct quadrupeds of Australia. But in all the bones described essentially marsupial characteristics are more or less determinable. The paper concludes with a summary of the characters of Diprotodon, throwing light upon the conditions of its extinction, its analogies with the Megatherium, its affinities to existing forms of Marsupialia, and the more generalized condition which it manifests of that mammalian type.

A table of the localities in Australia from which remains of Diprotodon have been obtained, and a table of the principal admeasurements of the skeleton, are appended to the text.

February 10, 1870.

Lieut.-General Sir EDWARD SABINE, K.C.B., President, in the Chair.

The Right Hon. Lord Napier of Magdala, and M. Charles Eugène Delaunay (Foreign Member) were admitted into the Society.

The following communications were read :

I. "On some remarkable Spectra of Compounds of Zirconia and the Oxides of Uranium." By H. C. SORBY, F.R.S. Received December 27, 1869.

When a scientific man has been led into an error and afterwards discovers his mistake, I think it a matter of duty that he should take an early opportunity to correct it. I therefore now write the following notice of certain remarkable peculiarities in the spectra of some compounds of the oxides of uranium with zirconia which led both myself and others* to conclude that they were due to a new elementary substance.

Though the spectra of the different salts of those bases which show wellmarked absorption-bands often differ in detail, yet they usually resemble each other so much that there is no difficulty in recognizing each particular element. This is so constantly the case in the various compounds of erbium, didymium, and cobalt, and in the ordinary salts of uranium, that for a long time the more I studied this question, the more did it appear to be a general rule, and there seemed to be no reason to suspect that a few special compounds of uranium would give spectra with absorption-bands as unlike as possible those of all others. Such, however, turns out to be the fact, when its oxides are combined with zirconia.

As an excellent illustration of important differences in mere detail, but general correspondence, I would refer to the spectra of didymium in different states of combination †, and would especially refer to the most distinct of the numerous absorption-bands which occurs in the yellow. The various compounds agree in showing this band in the same general position; but by careful management, and by the use of sufficient dispersive power, it may be resolved into a very variable number of narrow bands or black lines. For example, in the case of the crystallized sulphate containing comparatively little lanthanum, it can be resolved into seven narrow lines, two of those near the centre being the darkest, whereas when much lanthanum is present, one line on the side next the green is so much darker than the rest that the others are comparatively absent. On fusing the mixed oxides with borax, the same spectrum is seen as with oxide of didymium alone, and I can resolve the above-named band into only two narrower bands; whereas when the saturated bead is made to deposit crystals by being kept some time at a very dull red heat, this band can easily be resolved into eight equal and very distinct black lines. Although these and similar differences in detail are of much interest, yet in no case are they so considerable as to prevent our recognizing at once that the spectra are all due to didymium. It is also important to notice that the amount requisite to give a most splendid spectrum when the bead is crystalline will scarcely show any trace of bands when it is in a vitreous condition, dissolved in the borax. This is * Professor Church, Chemical News,' vol. xix. p. 121, and Professor Loew, ib. vol. xx. p. 9.

† See also Bunsen's paper, Pogg. Ann. vol. cxxviii. p. 100.

analogous to what occurs in the case of solid and powdered crystals of sulphate of didymium; for the absorption-bands in the spectrum of the light transmitted by a thin layer of the fine powder, strongly illuminated from the other side, are as distinct as in that transmitted by a many times greater thickness of solid and transparent crystal. We may very conveniently take advantage of this fact in studying the spectra of such substances, when the amount of material at command is otherwise too small. This seems to be because the transmitted light does not simply pass through the crystals, but is in great measure reflected from them backwards and forwards, and thus, as it were, passes through a greater thickness. It is also to a considerable extent similar to that reflected from the powder when illuminated from above, as may be clearly proved by what occurs in the case of uranic salts. These when in a state of moderately fine powder transmit light, giving a spectrum showing not only the absorption-bands in the blue, which alone are met with in that transmitted by a clear crystal, but also the bands in the green, which depend on fluorescence, characteristic of that reflected from the powder*. These two kinds of bands can be easily distinguished by means of a plate of deep blue cobalt glass, which has an entirely different action, according as it is placed below or above the object when the bands are due to fluorescence, but has no such effect when they are due to ordinary absorption. It would perhaps be well to mention here that I have in this manner proved that the abnormal bands seen in the spectra of the compounds of zirconia with the oxides of uranium described in this paper are due to genuine absorption, and not to fluorescence.

The remarkable spectrum of some jargons has been already described by me in the 'Chemical News 't, and in the Proceedings of the Royal Society. One of its most striking peculiarities is that when light passes in a direction perpendicular to the principal axis of the crystal, and the spectrum is divided by means of a double-image prism into two spectra, having the light polarized in opposite planes, though some of the absorption-bands are of equal intensity in both images, yet others are comparatively absent, some in one and some in the other; whereas in the case of other dichroic crystals which give spectra with absorption-bands, they are usually all more distinct in one image than when the light is not polarized, and all fainter, or even comparatively absent, in the other. No sooner had I observed this spectrum (No. 5, given below), than I made various experiments in order to ascertain whether uranium was present or not; and the then known tests that could be applied to the amount of material at my command seemed to show that it was absent. This was quite in accord with the results of the various analyses published by other chemists, none of whom mention the existence of any trace of that substance. Moreover the general character of the spectrum was entirely unlike that of all the known compounds of uranic oxide. The various artificial salts all agree in giving a variable but small * See Stokes's papers, Phil. Trans. 1852, p. 463, and 1853, p. 392. † Vol. xix. p. 122. Vol. xvii. p. 511.

number of moderately broad absorption-bands in the blue end (Nos. 1, 2, and 3); and the same is also seen in the case of several natural minerals; whereas the jargon gave a most unusually large number of narrow black lines (fourteen quite distinct, besides others more faint, and a single broader band which I cannot separate into lines), extending from the red end, so that nearly all occur in that part of the spectrum which is entirely free from bands in all previously known compounds of uranic oxide. This same general fact was also seen in the spectrum (No. 6) of the opaque blowpipe-beads gently flamed, as described in my former paper. These differences will be better understood by means of the following drawing, which shows three of the most striking spectra of uranic salts, that of uranate of soda, and the two which are rendered so abnormal by the presence of zirconia.

Spectra of Uranic Compounds.

No3. 1, 2, and 3. Uranic salts of the common type, viz.:

No. 4. Uranate of soda in the carbonate-of-soda bead.

Nos. 5 and 6. Uranic compounds with zirconia, viz. :—
5. Jargon after ignition.

6. Crystalline borax blowpipe-bead.

I will not now enter into a description of the various chemical and physical facts which seemed to warrant the conclusion that zircons sometimes contain a new earth; but taking these into consideration, there seemed

VOL. XVIII.

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