6. In middle and western Europe the barometric pressure appears to decrease everywhere from the month of January to the spring, usually attaining a minimum in April; it then rises. slowly but steadily to September, and sinks rapidly to November, when it usually reaches a second minimum. In summer, therefore, the whole atmospheric pressure gains more by increased evaporation than it loses by expansion. This over-compensation is probably to be explained, as we have seen above, by the lateral overflow received in the upper regions from Asia. In Sitka the whole annual curve is convex, a result only found in Europe at considerable mountain elevations, where it is a consequence of the expansion, and extension upwards, of the whole mass of the atmosphere in summer.

7. The region of great annual barometric variation, on the Asiatic side of the globe where monsoons prevail, extends much further to the north in the northern hemisphere, than it does to the south in the southern hemisphere; for the variation reaches its maximum at Pekin, while at Hobarton, in nearly a corresponding latitude, it has already become inconsiderable; and it is generally greater in the northern than in the corresponding southern latitudes. The exact contrary is the case on the Atlantic side and in the region of the Trades; for here the annual variation, though nowhere very considerable, is decidedly greater in the southern than in the northern hemisphere, as is shown by the results of observation at the Cape, Ascension, St. Helena, Rio Janeiro, and Pernambuco, compared with the West Indian Islands and the southern parts of the United States. Hence it follows, that if we compare places in the same latitude, we find but little difference between the annual variation in the southern Atlantic and southern Indian oceans, while in the northern hemisphere we have in the same latitude the very large annual variation in the north part of the Indian and in the Chinese seas, and the almost entire absence of annual variation in the Atlantic (compare Chusan with the Azores and Madeira). The explanation of the last named phenomenon, i. e. that of the northern hemisphere, by a lateral overflow in the upper parts of the atmosphere, seems so direct, that I think we may pronounce the irregular form of the annual barometric curve in the West Indies to be a secondary phenomenon, the primary causes of which must be looked for on the east.

8. It is known that in the eruption of the Coseguina on the 20th of January, 1835, when the isthmus of Central America was shaken by an earthquake, not only were volcanic ashes carried to Kingston in Jamaica, a distance of 800 English miles in the opposite direction to the trade wind, but some of the same ashes also fell 700 miles to the westward, on board the Conway, in the Pacific Ocean. We infer, therefore, that in

the higher regions of the atmosphere in the tropics the air is not always flowing regularly from S. W. to N. E., but that this usual and regular direction is sometimes interrupted by currents from east to west. I think I have indicated the probable cause of such anomalous currents in the above described barometric relations of the region of the monsoons compared with that of the trades. If we suppose the upper portions of the air ascending over Asia and Africa to flow off laterally, and if this takes place suddenly, it will check the course of the upper or counter current above the trade wind, and force it to break into the lower current. An east wind coming into a S. W. current must necessarily occasion a rotatory movement, turning in the opposite direction to the hands of a watch. A rotatory storm moving from S. E. to N. W. in the lower current or trade, would in this view be the result of the encounter of two masses of air impelled towards each other at many places in succession, the further course of the rotation (originating primarily in this manner) being that described by me in detail in a memoir "On the Law of Storms," translated in the Scientific Memoirs, vol. iii, art. 7. Thus it happens that the West India hurricanes and the Chinese typhoons occur near the lateral confines on either side of the great region of atmospheric expansion, the typhoons being probably occasioned by the direct pressure of the air from the region of the trade winds over the Pacific into the more expanded air of the monsoon region, and being distinct from the storms appropriately called by the Portuguese "Temporales," which accompany the outburst of the monsoon when the direction of the wind is reversed. The fact of the rotatory storms being of much more rare occurrence in the South Atlantic Ocean arises from the more equal distribution of the periodically diminished atmospheric pressure in the southern as compared with the northern hemisphere. Here, therefore, the rotatory storms take place principally in the monsoon itself.

9. It is evident that the unsymmetrical distribution of land and sea, which gives rise to the abnormal variations in the forms of the isothermal lines, is at the same time the principal cause of the movements of the atmosphere. Thus the monsoon is but a modification of the trade wind, of which the cause is to be sought in part beyond the tropic. The region of great thermic expansion of the air in summer in the interior of the continent of the Old World presents all the characteristic marks of the region of calms, being a centre towards which all adjacent masses of air are drawn. Hence there is no complete sub-tropical zone, in the sense of a zone encompassing the globe. The region over which the heated air ascends does not therefore move up and down, or north and south, parallel with the sun's change of declination, but has rather a kind of oscillatory movement, in which the West Indies represent the fixed point, and the greatest ampli

tude of oscillation is on the side of India. The northern excursion is much greater in the northern hemisphere than is the southern excursion on the side of the southern hemisphere. The European atmospheric relations, especially in summer, are therefore essentially of a secondary nature; and we must regard the little alteration in the atmospheric pressure in the course of the year in Europe as a secondary result, of which the explanation would not have been possible without the observations from Asia and Australia.

Berlin, January 5, 1853.

ART. VII. On the Composition of Eggs in the series of Animals-PART I. By A. VALENCIENNES and FREMY.*

ANATOMISTS who undertake new researches on the eggs of animals, are obliged, while extending their investigations to the different species of the animal series, to recur to the periods, now distant, of the publications of Prevost and Dumas, and of Charles Ernest Baër. The discovery of the former confirmed the opinions of William Cruikshanks, founded on observations and exact experiments; and that of M. Baër, who succeeded in seeing the first rudiments of the ovule, even under the stroma of the ovary of mammals, made one step more in Ovology.

That distinguished anatomist, while aiming to follow the evolution of the foetus, not only in the eggs of animals of that class, but in the different members of the animal kingdom, did not attempt to ascertain the nature of the liquids, more or less dense, of the egg, nor of those bodies held in suspension or dissolved in these liquids.

The same direction was pursued by those anatomists who have treated this subject before and after M. Baër. We should digress too much if we were to give a history of their successful labors. We believe it useful however to recall the course followed by the clever anatomist of Konigsberg and by his successors, in order to explain how it is that no one has yet investigated what the microscope has discovered in the vitellus (the yolk) of different eggs. It seems to us beyond a doubt that M. Baër saw the granular yolks of different kinds of ray fish and sharks, without studying them in detail. He did not try to discover their real nature by the aid of chemical analysis. He limited himself in fact, to saying that the yellow consists of a viscous liquid, of colorless grains of albumen, and of fat almost always divided into minute drops. This yellow is surrounded by white, but M. Baër did not try whether it would coagulate

* Translated from the Journal de Pharmacie, &c., May, 1854, p. 321, by Dr. J. Rosengarten, for this Journal.

like that of the egg of a chicken. In a word, this investigator saw in the eggs of these cartilaginous fishes, and in those of other animals, a mixture of principles as in the eggs of birds, always consisting of a yolk or vitellus, covered with white liquid albumen, and all contained in an external membrane as much varied in its nature as in color. We have reason for believing too, that M. Vogt perceived some vitellin grains in the yolk of the toad, Palytes obstetricans, Dum. He is however, less precise than M. Baër. It is also believed that M. Strauss saw the vitellin granules, of which we shall speak in our second paper, since he described in his beautiful work on the anatomy of the Cockchafer, the yolk of eggs of these Coleoptera, as formed of a liquid pulp, composed of granules, and showing on the surface of the envelop of the egg a layer of globules. There are allusions to these granules in the work of Baudrimont and Martin Saint-Ange, which was crowned by the Academy of Sciences. But these authors did not separate them from the rest of the yolk to make them the subject of special study; they pointed them out in the midst of the drops of oil which swim in the yellow of the eggs of frogs. Other naturalists who have studied the eggs of different Annelids, Helminths, Insects, Arachnids, Crustacea, Molluscs (either Cephalopods, Gasteropods or Acephalous), speak of globules, without distinguishing them from drops of fat, and, which is more important for the subject of this article, without marking any vitellin substance.

M. Dumas and Cahours were the first who clearly distinguished in the egg of a hen, a particular proximate principle, the yolk, characterised by its physical properties and by its composition as deduced from chemical analysis. Their researches were not pushed further, and they were satisfied by calling by the same collective name of egg, all the products of the ovary that serve in any animal, after its fecundation, for the reproduction of individuals like the parent animal which secreted them.

On examining attentively the eggs of numerous oviparous animals, anatomists however have observed marked differences, which prove that these reproducing bodies are as varied as the animals to which they give birth. Thus,-only to cite a few facts,-the absence of the allantoid in the eggs of oviparous animals living in the water, was long ago remarked; the want of chalazes, the thin vitellin membrane detected with difficulty under the microscope taking its place; and as, one of us has observed, many kinds of eggs do not harden by cooking in boiling water.

The Academy long ago acknowledged the necessity of calling the attention of men of science to the investigation of this subject, by proposing to the meetings, questions relating more or less definitely to the particular composition of eggs. It has been fortunate to find in many communications addressed to it, a portion of the desired answers.

Feeling ourselves the importance of making additions to the researches already brought forward on the composition of eggs, we have undertaken this task together, the questions which it raises being partly zoological and partly chemical.

A subject so vast, which needs the continuous study of eggs of animals belonging to different classes of the animal kingdom, cannot be exhausted in one article; we are far too, from considering our researches as completed.

We propose in this memoir, to describe the differences which exist in the composition of eggs, and to lay down some general principles, to be developed in subsequent communications.

1. Eggs of Birds.

What we have said at the commencement of this article sufficiently explains our silence as to the composition of hen's eggs during the evolution of the foetus, and as to former researches relative to the membranes which envelop the first formation of the chicken within the egg. We will here examine only the nature of the two substances, the white or albumen, and the yellow or vitellus, in order to start from this point of comparison in studying the eggs of other animals. We shall not follow strictly the order established by zoologists for the animal series, though we shall not depart widely from that order.

'The composition of birds eggs has been clearly established by numerous authors, first by Vauquelin, Bostock, and then by Chevreul, John, Dumas and Cahours, Lecanu, Gobley, Martin St.-Ange and Baudrimont, Scheerer. And in this part of our researches, we are satisfied to confirm the exactness of the leading facts announced by the observers we have cited, and to determine with precision the specific characters of birds eggs.

The white of birds egg is considered by almost all chemists as a principle itself pure, though this white has in it various salts and a sulphurous body which can be separated from the albumen by different reagents without producing the decomposition of that substance, as was long ago shown by Chevreul.

In examining the white taken from eggs of different kinds of birds, we have often noticed that this body has varying properties. In some kinds, it is almost fluid; in others, it possesses a gelatinous consistency. The white of the egg of a hen is, after boiling, opaque, and of a pure color, white and solid. That of the lapwing becomes after cooking, transparent, opaline, greenish, and so hard that it may be cut into little stones, used in certain parts of Germany for common jewelry.

These peculiarities are not enough to prove that the white of birds eggs is formed of different albumens, but they seem to show that attentive researches will enable us to point out new properties in these albumens, which have hitherto escaped chemists.