"2. Experiments with Lime.-A platinum wire of the same thickness as the last was moistened with the phosphoric acid, some calcium nitrate was then taken up in the loop, and heated in the hydrogen flame until a residue of lime was obtained. At the outset the calciumspectrum was observed; but the light speedily gave only a continuous spectrum. The lime and loop of wire were kept well enveloped in the hydrogen flame for nearly half an hour, in order to ensure the complete decomposition of the nitrate. During this time no lines could be detected on the background of the continuous spectrum, or in the spectrum of the flame surrounding the lime. More hydrogen was now turned on and oxygen slowly admitted, the light being examined with the spectroscope during the time. When the proportion of oxygen had reached a certain point, faint traces of the two brightest Ca lines appeared on the bright background; and the intensity of these lines increased with the amount of oxygen admitted, up to a definite extent. When a certain proportion of oxygen was exceeded, the lines became less distinct. The best results were obtained when the hydrogen was decidedly in excess of the oxygen in the flamethat is to say, more than in the proportion of 2: 1.

"When the slit of the spectroscope was pointed in such a way that only the light from the flame surrounding the incandescent lime entered the instrument, all the Ca lines and bands were observed with great ease without a continuous spectrum. On looking at the mantle of flame with the naked eye, it was easy to perceive a reddish tinge. I next maintained the small fragment of lime at the highest temperature its supporting wire was capable of resisting for three hours; at the end of this time the Ca lines were as strongly marked as before, and the lime on the wire had very appreciably diminished in amount. The same results were obtained when no phosphoric acid was employed to attach the calcium nitrate to the wire in the first instance.

Again, a piece of well-burned quicklime, of very small size, was heated alone on a platinum wire for more than an hour; and the bright Ca lines were seen during the whole time.

"From the results of these experiments we must draw the conclusions: (1) that when lime is sufficiently heated the light which it emits is derived in part from the incandescent solid, and partly from ignited vapour; (2) that lime is either volatile as such, or that in the first instance it suffers reduction by the excess of hydrogen in the flame, the luminous vapour of calcium then giving its own peculiar spectrum. "3. Experiments with Erbia.-The specimen of erbium nitrate which you kindly gave me was attached to a platinum loop with syrupy phosphoric acid as usual, and decomposition of the salt effected in the plain hydrogen flame. After heating for a short time in this way, the chief green line of erbia became visible, but seen upon the continuous spectrum. Oxygen was now turned slowly into the flame. As the temperature rose, two of the other bright lines of the earth were seen. The best observations were made when the oxyhydrogen flame had hydrogen in excess, and the erbia was kept in such a position that it was very strongly ignited. The

erbia lines were most distinctly seen when the slit of the spectroscope took in the light from the extreme edge of the incandescent solid. When the bright lines were best observed, the continuous spectrum was relatively faint. Again, when the slit was made to cut the edge of the ignited bead of the earth, the strong green line of erbia was seen to extend to a very small but appreciable distance above or below (as the case might be) the continuous spectrum. I could only observe this for the strong line. I failed to get any trace of lines in the spectrum of the flame beyond the incandescent erbia.

"The erbia was next heated in the oxyhydrogen flame to the maximum temperature that the wire would bear for three and a half hours; but the green line was seen to be just as strongly marked at the end as at the beginning of the experiment. The bulk of the erbia was so much reduced by this treatment, that I have now scarcely a trace left.

"From the results of these experiments, I think we must conclude (1) that the light emitted by incandescent erbia is derived chiefly from the ignited solid, but that the bright lines observed in its spectrum have as their source a luminous vapour of extremely low tension at even the highest temperature of the oxyhydrogen flame; (2) that this interrupted spectrum belongs either to erbium or to its oxide.

"If these conclusions are true, it follows that erbia is not an exception to the ordinary law.

"It would appear that in these experiments three substances have been employed, varying in their degree of volatility. At the temperature of the oxyhydrogen flame magnesia appears to be less volatile than lime; but I am in doubt what relative volatility to assign to erbia, since its spectrum of bright lines can be seen when the earth is heated in the plain hydrogen flame, and yet at the much higher temperature of the oxyhydrogen jet the volume of luminous vapour does not appear to materially increase.

Finally, we have yet to learn whether or not in all these cases reduction of the oxide precedes volatilization; if reduction takes place, the luminous vapour must be that of the metal. The settlement of this question would no doubt be very difficult. But I rather incline to the view that the vapour whose spectrum is obtained on igniting these earths is that of the metal; for I find that the bright lines are most easily observed when hydrogen is present in excess in the oxyhydrogen flame. Moreover the actual amount of matter volatilized on very prolonged heating is really very small; and this circumstance appears to favour the view that a slow surface-reduction is in progress.

GEOLOGICAL SOCIETY.

[Continued from p. 227.]

March 23rd, 1870.-Warington W. Smyth, Esq., M.A., F.R.S., Vice-President, in the Chair.

The following communications were read :—

1. Professor Huxley communicated a letter received by him from Dr. Emanuel Bunzel, of Vienna, giving a short account, illustrated with figures, of the posterior portion of a skull obtained by Professor Suess from a coal-mine of Upper Cretaceous (Gosau) age. Dr. Bunzel stated that at the first glance this skull appeared to possess Reptilian characters, but that the convexity of the occiput, and its gentle passage into the roof of the skull, the presence of a transverse ridge in the occipital region, the absence of sutures, the globular form of the condyle, and some other peculiarities prevent the animal to which this skull belonged from being referred to any known order of Reptiles. The author compared this fragment of a skull with that of a bird, and suggested the establishment of a new order of fossil Reptiles (Ornithocephala), closely related to Prof. Huxley's Ornithoscelida. He proposed to refer his fossil to a new genus, which he named Struthiosaurus.

2. "On the Discovery of Organic Remains in the Caribbean Series of Trinidad." By R. J. Lechmere Guppy, Esq., F.L.S., F.G.S.

The author described the rocks of the "Caribbean Group" as consisting of gneiss, gneissose, talcose, and micaceous slates, and crystalline and compact limestones, and remarked upon the probable distribution of rocks of the same series on the continent of South America. In Trinidad the uppermost member of the series is a compact dark blue limestone, which contains obscure but very abundant fossils ; in the subjacent clay-slates and quartz rocks calcareous strings and bands containing more distinct traces of organisms occur. The author believed that he had detected an Eozoon (which he called E. caribbeum), a Favosites (named F. fenestralis), a Coral, and fragments of Echinoderms. He considered it probable that the Caribbean series was pre-Silurian.

3. "On the Paleontology of the Junetion-beds of the Lower and Middle Lias in Gloucestershire." By Ralph Tate, Esq., A.L.S., F.G.S.

The object of this paper was to show that the attachment of the zone of Ammonites raricostatus to the Lower Lias and that of A. Jamesoni to the Middle Lias harmonizes with the distribution of the organic remains: 50 species were catalogued from the united zones of A. oxynotus and A. raricostatus, 8 of which pass up into the Middle Lias, whilst 13 occur in the lower horizons; 115 species were enumerated as occurring in the zone of Ammonites Jamesoni, 60 of which pass to higher zones, whilst 11 made their first appearance in the Lower Lias,-the number of species common to the contiguous zones being 14.

The author inferred that, as the conditions of depth and deposit of the upper part of the Lower Lias are repeated in the lower part

of the Middle Lias, accompanied by a total change in the fauna, a break in the stratigraphical succession existed between the Lower and Middle Lias. This view is supported by the fact of the numerical decrease of species in passing up through the several stages of the Lower Lias, and that of the introduction of many new generic types with the zone of Ammonites Jamesoni. Many new species were described.

4. "Geological Observations on the Waipara River, New Zealand." By T. H. Cockburn Hood, Esq., F.G.S.

In this paper the author described the general features of the locality from which he has obtained bones of Plesiosaurus, Ichthyosaurus, and Teleosaurus. The bones were not obtained in situ, but from large boulders and blocks scattered in the ravines of the Waipara and its tributaries.

5. R. H. Scott, Esq., F.G.S., communicated an extract from a letter addressed to him by M. Coumbary, Director of the Imperial Observatory of Constantinople, containing an account received from M. L. Carabello of the reported fall of a large meteorite near Mourzouk, in the district of Fezzan, in lat. 26° N., and long. 12o E. of Paris. It fell on the evening of the 25th December last, in the form of a great globe of fire, measuring nearly a metre in diameter; on touching the earth it threw off strong sparks with a noise like the report of a pistol, and exhaled a peculiar odour. It fell near a group of Arabs, who were so much frightened by it, that they "immediately discharged their guns at this incomprehensible monster."

XL. Intelligence and Miscellaneous Articles.

EXPERIMENTAL RESEARCH ON THE INFLUENCE OF HEAT ON ELECTROMOTIVE FORCE. AY DR. L. BLEEKRODE.

THIS question has already been the object of the researches of several physicists. Until the present time, only three cases have been considered—(1) when metals are placed in contact with acids, (2) saline solutions with one another, (3) metals with their saline solutions.

Faraday commenced this investigation in 1840*. He heated one of the branches of a U-tube containing an acid in which two identical metallic wires were immersed. The current was strong when the metal was attackable, weak when gold or platinum was used: in the latter case Faraday considered the current thermoelectric. Wild experimented on liquids in contact with one another. He still considered the current to be thermoelectric, but he tried in vain to reproduce with liquids the phenomena of Peltier.

Lindig placed in contact two electrodes of the same metal with a solution of that metal; he confined himself to zinc and copper, because he proposed to investigate whether the electromotive force of Daniell's battery varies with the temperature.

* Philosophical Transactions, 1840.

† Pogg. Ann. vol. ciii. p. 353 (1858).

Ibid. vol. cxxiii. p. 1 (1868).

Dr. Bleekrode has varied these experiments considerably. He immersed two electrodes of the same metal in two vessels containing a salt of this metal, united by a siphon. One of these vessels was maintained at nearly a constant temperature, whilst the other, placed in a hot air-bath, was gradually heated. The electrodes were connected by a circuit, including a coil whose resistance was such to render imperceptible the variations produced by heat in the conductivity of the liquid; and in the second place a reflecting galvanometer, the deflections of which never exceed 3o, measured directly the intensities. As the resistance of the circuit remained sensibly constant, these deflections were also proportional to the electromotive forces.

The memoir by Dr. Bleekrode is very rich in numerical results. These results are collected in twenty-one Tables, of which the majority are represented by curves. Some of these curves do not differ much from the straight line, so that the electromotive force is proportional to the difference of the temperatures; this is what takes place, for instance, with copper in sulphate or nitrate of copper, and with amalgamated zinc in sulphate or chloride of zinc; but it is rarely like this.

In general the current goes through the siphon from the cold vessel to the heated vessel, except with silver immersed in acetate or nitrate of silver, when it is in a contrary direction.

The most curious cases are those in which the current changes sign. Of these the author distinguishes three. When amalgamated zinc is immersed in a solution of double cyanide of zinc and potassium, the current is at first positive or passes from cold to hot; then it changes direction when the difference of temperatures exceeds 30°; it is the same at 53° for silver in double cyanide of silver and potassium. Lead in nitrate of lead is still more singular: the couple is at first negative (the current passes from hot to cold); then it changes direction when the difference of temperatures exceeds 21°, and again changes and becomes negative when the difference reaches 51°.

Too much importance must not be attached to the numerical determinations of electromotive forces, because the composition of the liquids changes under the action of the current, and soon produces other currents which are superposed on the first and produce heterogeneity of the solutions in which the electrodes are immersed. This phenomenon is particularly remarkable with silver immersed in nitrate of silver. Although in this case the current passes from hot to cold, it produces in the heated vessel some free acid at the same time that it deposits some metallic silver, partly black and partly crystallized under an arborescent form.-Poggendorff's Annalen, vol. cxxxviii. p. 571; Annales de Chimie, April 1870.

ON TESTS FOR THE PERFECTION AND PARALLELISM OF PLANE SURFACES OF GLASS. BY WOLCOTT GIBBS, M.D., RUMFORD ProFESSOR IN HARVARD UNIVERSITY.

When a plano-convex lens of long radius of curvature is placed