simpler hypothesis" will account for the chemical phænomena accompanying volcanic action, and Dr. Davy himself not having supplied this desideratum, I cannot view his adoption of it in any other light at present than as a matter of taste on his part. Dr. Davy, indeed, makes his brother say, though I have not yet lighted upon the passage in which this sentiment occurs, that the chemical theory does not rest on sufficient evidence.

This however, although a ground for scepticism as to the truth of the one, would afford no reason for adopting the other; for granting that of two hypotheses both competent to explain the facts, the simpler one ought to be preferred, no competition surely can exist between them, when this can be predicated only of one.

That the chemical theory will enable us to account for the phænomena, has been shown in the memoir which called forth Dr. Davy's animadversions, and since more fully elsewhere*, and is admitted, as has been seen, in the fullest manner by Sir Humphry in the very paper to which allusion is made. Neither do I see the force of the negative evidence which Dr. Davy has produced to impugn it, for he is too conversant with volcanic operations to be ignorant that sulphuretted hydrogen is amongst its commonest products, and is too good a chemist to admit the possibility of substances like potassium or calcium in their unoxidized condition finding their way upwards in the midst of the steam, which always accompanies volcanic ejections +. What, then, becomes of the objection, that if the hypothesis were correct, inflammable gas might probably be detected issuing from the volcano, or that some pure or uncombined alkaline or earthy inflammable basis might be discovered entangled in the lava, when the former is seen to be actually present, and the latter can so little be expected? And, whilst the presence of hydrogen, combined as it naturally would be with the sulphur which we know to exist in such situations, furnishes a striking confirmation of Sir Humphry Davy's original views, neither he, nor any other chemist, has succeeded in accounting for it according to the opposite ones.

The same may be said of the sal ammoniac, the nitrogen, and according to the simplest form of the hypothesis as ex

Encyclop. Metrop., art. GEOLOGY.

+ This objection, at least, cannot have originated with Sir Humphry, but must be the exclusive property of his brother, for in the memoir referred to we find Sir Humphry distinctly asserting, "That the extreme facility of oxidation belonging to these bodies, must prevent them from ever being found in a pure combustible state in the products of volcanic eruptions."

pounded by Cordier, even of the water and the muriatic acid, which are noticed by Davy himself as issuing from the volcano, whose phænomena he describes.

Whatever ground, therefore, may exist for his scepticism on the subject, none certainly has been assigned for his adoption of the rival hypothesis, which, without effecting the object of explaining the facts, is saddled with assumptions equally gratuitous; the existence of the alkaline and earthy bases in the interior of the earth, being not more unsupported by direct evidence, than that of a central fluid mass; seeing that the increasing temperature detected in descending into the bowels of the earth, may be explained quite as well by chemical processes carried on at the requisite depths, as by the hypothesis of central fluidity.

I trust I have now said enough to justify my having stated that Sir Humphry only gave his ipse dixit in support of his new hypothesis, a point which I was at that time more particularly anxious to establish, from a wish to obtain for the theory I had advocated an unprejudiced hearing, and being well aware of the weight which the deliberate judgement of such an authority as that of Sir H. Davy on a question of science would obtain with most readers. Since that time the favourable opinion expressed by the present as well as by the late President of the Geological Society with respect to the chemical theory, will have secured it a candid reception amongst naturalists; whilst the authority of one of the most distinguished of Sir Humphry Davy's living cotemporaries and rivals in science, Mons. Ampère, will vindicate its claim to respect amongst chemical philosophers.-One more word with respect to the reasonableness of imagining that Davy might choose to abandon his former hypothesis without deliberate consideration.

In the first place, considering the numberless applications of which his great discovery of the alkaline and earthy bases admitted, it is not necessary to suppose that he would regard this one with any peculiar favour. And indeed the only allusion I find to it at all in any of his earlier publications consists of four lines in a note appended to his Memoir on the Decomposition of the Earths.

Secondly, the solid character of the discoveries on which the reputation of Davy was based, would naturally make him indifferent as to the fate of a theory resting on assumptions which, whether probable or not, were such as could themselves neither be substantiated nor set aside by direct experiment.

The higher, indeed, we estimate the fame of Sir H. Davy, the less difficult will it appear to us to account for his aban

donment of his original views, and for his preference as a matter of taste for others which were calculated, from their very vagueness, to allow full scope to that imagination, which, as appears from his Consolations of a Philosopher, continued in unimpaired vigour to the last. There is, therefore, no analogy between the motives of his conduct in this case and in the question with respect to the nature of chlorine, in which Sir H. Davy might feel a just pride, as having recalled the scien tific world from theory to a simple expression of facts, and thus corrected the logic of chemistry, in quite as great a degree as he extended our knowledge of this particular class of combinations.

It may be readily inferred from these remarks that I regard the chemical theory of volcanos, which it has been my humble endeavour to elucidate and to confirm, chiefly valuable by erecting a standard to which volcanic operations may be compared, and thus encouraging more minute attention to the phænomena they present. This the mere vague and general statement of their originating in central heat is not so likely to do, and hence it may perhaps be regretted, if the preference for a simpler hypothesis, or the authority of great names, should so prepossess the minds of men of science as to prevent their entertaining the views I have advocated, and to induce them to dismiss the subject as altogether beyond the reach of probable conjecture *.

It is on this latter ground chiefly that I have chosen to address you, for with respect to that part of the subject which concerns myself I should have been content perhaps to leave the question at issue to the candour of the public, and to the impression which most persons will entertain, that I at least can have no desire to attribute unworthy motives to Sir H. Davy.

Oxford, Feb. 23, 1836.

* In Dr. Thomson's Outlines of Mineralogy, Geology, and Mineral Analysis just published, I find this sentiment expressed, but the only objections stated to the chemical theory are, 1st, The specific gravity of the earth; 2ndly, The nature of the elastic fluids emitted by volcanos. I regret, there fore, that the learned author, who has done me the honour of quoting and commending the work on volcanos I published in 1826, had not also consulted the article on Geology in the Encyclop. Metrop., to which I contributed the portion relating to volcanos, as he would have there seen the first objection fully, and I hope fairly, treated, and the latter shown to be quite in accordance with the theory.

The low specific gravity of the metals of the alkalies appears to operate against the reception of the theory in the minds of many; yet if it can be shown that the bases of those volcanic products which appear upon the surface have collectively a greater specific gravity than the mass resulting from their union with oxygen, I cannot see wherein the force of this objection resides.

LI. Proceedings of Learned Societies.

LINNEAN SOCIETY.

Jan. 19, ing in the River Essequibo, and of the fish called Pacou,

1836.

which feeds upon these plants. By Robert H. Schomburgh.

Feb. 2.-Read, Observations upon a supposed new species of Veronica found in Staffordshire, in a letter to Mr. Sowerby; by Mr. George Luxford.

Also, descriptions of two species of the genus Pinus from the Himalaya Alps. By Professor Don, Libr. L.S.

The first of these, which belongs to the group of spruce firs, has been described and figured by Dr. Wallich, in the 3rd volume of his splendid work on Indian plants, under the name of Pinus Smithiana, in honour of the late eminent President of the Linnean Society. It is nearly related to Pinus orientalis, a native of Armenia and the western parts of Georgia, and has been cultivated for more than ten years in our gardens, and was at first supposed to belong to the Indian cedar (Pinus Deodara). Khutrow, Morinda, and Raga, are the names by which it is known in its native mountains.

The second species belongs to the group of silver firs, and is nearly allied to Pinus Webbiana, but is essentially distinguished from it by its longer acutely bidentate leaves, of nearly the same colour on both surfaces, by its shorter and thicker cones, with trapeziform scales, and rounded notched bracteolæ. Dr. Wallich, who had neither seen flowers nor fruit, has doubtfully referred it to Taxus, under the specific name of Lambertiana, in his Catalogue. Several travellers have noticed the tree, but Mr. Royle appears to be the only one who has been fortunate enough to meet with it in flower and fruit.

The author has noticed a remarkable peculiarity in the seeds of the species belonging to this group, which consists in the rupture or separation at the inner side of the external integument, leaving the nucleus with its inner covering exposed at that part.

The following are the characters of these two species :

P. foliis solitariis compresso-tetragonis rectis subulatis pungentibus, strobilis oblongis cylindraceis: squamis obovato-rotundatis coriaceis rigidis margine lævissimis, antherarum cristâ subrotundâ erosè crenulata.

Sp. 2. PINUS PINDROW. Royle MSS.

P. foliis bifariam versis linearibus planis utrinque concoloribus apice bidentatis, antherarum cristâ bicorniculatâ, strobilis ovalibus: squamis trapezoideo-cordatis, bracteolis subrotundis emarginatis erosè crenulatis. Feb. 16.-Read some observations on the Nephrodium rigidum. By Professor Don, Libr. L.S.

For this valuable addition to the British Filices, we are indebted to the Rev. W. T. Bree, who discovered it many years ago on Ingleborough, and it has since been published in the Supplement to English Botany. The British specimens accord entirely with foreign ones, and with the accurate figure given by Schkuhr (Kryptog. Gew. t. 38.).

The author has proposed the following character of the species : N. rigidum, fronde lanceolatâ bipinnatâ: pinnulis oblongis pinnatifidis: laciniis argutè dentato-serratis: venulis inconspicuis, soris biseriatim contiguis, indusio scarioso dilatato, stipite rhachique densè paleaceis. The species ranks next to dilatatum and spinulosum, but differs from both by its larger and more crowded sori, broader and more depressed indusium, and by the stipes and rhachis being copiously clothed with narrow ramentaceous scales as in Aspidium aculeatum. The more delicate fronds, with pinnatifid pinnulæ, having the lobes serrated with sharp-pointed, incurved teeth, essentially distinguish it from Nephrodium Filix Mas, between which and spinulosum it appears to be intermediate in its habit and characters.

Read also remarks on some varieties of Erica ciliaris and Tetralix. By Professor Don, Libr. L.S.

The extreme states of these two species are easily recognised at first sight; but it must be admitted that varieties do occur in which the characters of both appear blended. The normal form of ciliaris is characterized by its flat, ovate, ternary leaves, elongated axis of its inflorescence, oblong and slightly curved corollas, and naked anthers; and that of Tetralix by its quaternary, linear leaves, revolute at the edges, capitate inflorescence, globular corollas, and aristate anthers. Some of the varieties of ciliaris exhibited to the meeting, for which the author was indebted to Mr. Hewett C. Watson, had the axis of their inflorescence quite as much depressed as in Tetralix, along with the narrow quaternary leaves of that species. Another specimen, clearly referrible to Tetralix, had the corolla nearly as long as in ciliaris. Another variety of Tetralix, lately discovered in Ireland, and which by some botanists is regarded as constituting a distinct species, has entirely the habit of ciliaris, but with the depressed inflorescence, globular corollas and aristate anthers, of the former species; and it differs from both in the entire absence of the short pubescence from the upper surface of the leaves.

The only permanent mark by which ciliaris and Tetralix can be separated is by the absence or presence of the awn-like appendages at the base of the anthers.

A comparison of Irish specimens of Gypsocallis mediterranea with others contained in the Smithian Herbarium, shows that they agree in every essential point; and although the two plants when grown together in a garden exhibit a somewhat different aspect, there cannot remain any doubt as to their identity. G. carnea is readily distinguished by the much greater length of its anthers and ovarium.

GIBRALTAR SCIENTIFIC SOCIETY.-NEW OBSERVATORY AT

CATANIA.

It is truly gratifying to see that activity in scientific pursuits is fast spreading from Britain to her colonies. The institution at Quebec has already distinguished itself by the publication of some able papers on American geology, topography, and statistics; and we now find that a new society has started up at Gibraltar, which, we trust, may prove