deserts of Arabia, and from the foot of the Atlas Mountains, as far as the Cape of Good Hope, is strongly in favour of the hypothesis, that the whole of Central Africa, so far from being traversed by chains of lofty mountains, presents nothing but a series of sandy plains and deserts. The existence of the former would certainly prove an insurmountable barrier to the ostrich, though we are less positive with regard to the similarly distributed lion and elephant.

Our argument derives, however, the most solid and the most substantial support from an examination of the manner in which the various Faunas are distributed over the Continent of Africa. Generally speaking, the want of variety amongst them is very striking. In Asia the towering mountains of the Himalayah distinctly separate the Indian Fauna from that of Central and Northern Asia; and their respective Faunas are so unlike each other, that they scarcely admit of comparison. In a similar manner, the Andes of South America divide the Faunas of the eastern districts from those of the western provinces; and it is in vain to look for points of resemblance between the two. This is certainly not the case in Africa. The Faunas of Nubia and of Senegambia are materially the same, even as regards the identity of a vast number of species. So close a relationship between the Faunas of opposite coasts could hardly be accounted for, on the supposition that immense masses of mountain ranges, like those of the Himalayah, of the Andes, or even of our Alps, are interposed. Accordingly, if it can be proved that there exist similar relations between the various districts of Africa, which lie remote from each other; and that their Faunas are intimately connected with one another, not only in the directions of geographical longitude or latitude, but likewise in that of the diagonal; the well known hypothesis of Lacepede, according to which the interior of Africa is said to consist of a vast collection of mountain chains, is then completely refuted on the other hand, the opinion of Professor Ritter becomes more firmly established, according to whom the interior of Africa is a large table-land encompassed by ranges of hills, and no doubt interspersed with mountains, but which are so loosely united, and of such secondary importance, that the Faunas may easily traverse them in

every direction. The researches published in Mr Wagner's Travels through the States of Algiers, vol. iii. p. 140, clearly demonstrate that there is a striking resemblance between the Fauna of those districts of Africa which extend along the Mediterranean, and the Fauna distributed over the opposite coast of Europe, with the exception, however, of a few species, which are confined to the former. The States of Barbary are distinctly separated from the southern countries of Africa, not so much, as one might fancy, by the chains of Mount Atlas, as by the desert of Sahara. The Fauna of Egypt is more closely related to that of the other districts of Africa, than to that of the States of Barbary; and when single forms are distributed from thence to other parts of Africa, it is only through Egypt. We have already alluded to the great affinity traceable between the Egypto-Nubian Fauna, with which that of Sennaar and Kordofans forms the connecting link, and the Fauna of Senegambia. Guinea, which, among the magnificent Fauna of its lowlands, certainly claims some species as entirely its own, for instance the genuine Goliaths, agrees on the whole with the countries of the Senegal, because a great many species are found to be, to a certain extent, common to both. The Fauna of South Africa is apparently more isolated.

This is owing partly to the circumstance that it embraces several species of its own, partly to the peculiar mode of distribution by which the general relations of the Fauna are more or less affected. We allude, in the present instance, to the predominance of the Melasomas, to the frequent occurrence of small Melolonthidæ, &c. Hence we have ample reason to expect here an independent Fauna system. The fact, that several species, common to the tropics of Africa, to Guinea and Senegambia, are found again in great abundance at Christmas Bay, as also in the vicinity of Cape Town, might confirm us in the belief that there are no mountains intervening, at least none large enough to effect a division between the Faunas. So long, however, as we are left in ignorance with regard to the condition of the countries extending from the Gulf of Guinea to the Cape of Good Hope, or even with regard to particular localities, so long shall we be prevented from determining the exact relation

which the Fauna of the Cape bears to that of other countries of Africa.

Under these circumstances, a small collection of insects, formed in the Portuguese possessions of Angola, and presented to the Royal Entomological Museum by the Privy Councillor of Medicine, Dr Schönlein, has created considerable interest, as it promises to enlarge our knowledge of Africa. A careful examination has led to the conclusion, that the Fauna of Angola stands between that of the Senegal and of Guinea, on the one hand, and that of the Cape on the other, since it embraces not only a great number of species, but likewise several characteristic genera, which are common to those countries, and since it forms the connecting line between the Fauna of South Africa, and that of its central regions. We are indebted for this collection to Mr Edward Grossbendtner. This gentleman, honoured by the support and patronage of Dr. Schönlein, accompanied the Consul-General, Dos Santos, on a commercial expedition, consisting of six vessels, and had thus an opportunity of visiting the Portuguese settlements of Angola, Benguela, of St Paolo de Loanda, and of the independent negro empire of Ambriz.

This enterprise turned out to be unsuccessful, more especially as the Commander himself was carried off by the effects of the climate. The expedition arrived in Benguela on the 10th October, the weather being then very favourable. The sight of a luxuriant vegetation, and a temperature of about 90°, seemed to hold out the most flattering prospects; but the naturalist, Mr Grossbendtner, and the botanist, Mr Wrede, were unexpectedly detained on board, and afterwards towards the end of October, when many Europeans perished from diseases caused by the rainy season, both gentlemen fell victims to their enthusiasm. According to the catalogue published by the Privy Councillor of Medicine, Dr Schönlein, the collection of Grossbendtner, who, during his few days of good health, spared no trouble in bringing it together, consists of 2140 specimens of Coleoptera belonging to 173 species, and of 20 butterflies. Part of it has probably been lost, because, from the time of his death, no one on board of the ship took an interest in the preservation of these curiosities.

Considering how little we are acquainted with the Fauna of that portion of Africa, which is situated between the equator and the tropic of Capricorn, a closer examination of this small collection cannot but furnish matter for very interesting observations.* A few species only have hitherto been published, in particular by Messrs Olivier and Laporte (Hist. Nat. d. Ins. Suit. à Buff., where Dongola seems sometimes to have, by mistake, been substituted for Angola.)

It is impossible to give a detailed account of the various relations of the Fauna, until a collection has been subjected to a thorough and minute investigation. Obscure species, as well as those generally known and widely diffused, are in that case of equal importance with those newly discovered or looked upon as great rarities.†

On the Incipient Disengagement of Elastic Fluids. BY JOHN THOMAS WOODHOUSE, M.D., Senior Fellow of Caius College, Cambridge. Communicated by the Author.

I have never seen or heard a satisfactory explanation of the well-known fact, that when a tea-kettle with boiling water in it, is removed from the fire, the bottom is only moderately warm. It has been referred to like causes (substituting steam for vapour), as when spirits are thrown upon the skin, and a sensation of cold is produced, in which case heat is first given to the fluid, succeeded by a change in the state of the fluid.

This explanation appears to me defective and unsatisfactory; and I will now endeavour to shew where it is defective, and supply the defect.

When the kettle boils, the water in it will raise the thermo

* The few butterflies are not worth considering, because, being chiefly species of Antocharis and Lyosena, they exhibit nothing characteristic of the Fauna of Angola.

199.

↑ From Erichson's Archiv für Naturgeschichte, 1843, part 3d, p. We hope, on a future occasion, to lay before our readers Professor Erichson's particular details.-Edit.

meter to 212° Fahrenheit; the fire is much hotter, and yet the hand which soon after touches it, feels only a moderate warmth -in a short time the heat becomes intolerable, i. e., of the same heat as the superincumbent fluid.

Now, admitting when the heat of the bottom is becoming greater than 212°, that the water undergoes a change by its conversion into steam, and that the heat of the contents of the kettle is thus partly latent,-admitting, that this would account for the bottom not indicating a greater heat than 212°, I contend, it is unequal to explain, why the bottom should be less than 212° for the water is 212°, the steam under the ordinary pressure of the atmosphere is supposed to be 212°, and the fire which was under it more than 212°. The object of this paper is to explain, why the bottom immediately on its removal from the fire, should indicate a heat less than 212o, and soon after, a heat equal to that of the water in it. Fig. 1. Let w represent a portion of

Fig. 1.

wr, represent the space occupied by the steam, into which this portion is converted by the communication of heat. The heat of the steam filling this sphere would be 212°; but, in explaining the object of this paper, I suggest that the heat of the steam may be less than 212°, and to establish this, I propose the following theory:—

I assume, that when a portion of water is converted from its fluid into its gaseous state, a sudden expansion, or what may be termed, an explosion happens, i. e., supposing the steam in its quiescent state, and under the ordinary pressure of the atmosphere, would occupy the sphere wr, at the instant of its conversion-by its elasticity, or momentum of its particles, it proceeds to fill a sphere whose radius is w r', which is greater than nr.

Now, according to the acknowledged doctrine of latent heat, when water receives heat, which converts it into steam, the steam under atmospheric pressure would occupy a space varying with the quantity of caloric imparted to it. By the same doctrine of latent heat, if the same quantity of steam under the