And Mr. Ersted acknowledges his obligations to the same work. This may serve, in some measure, to account for the similarity of our opinions.

The primary compounds, or the corps brulées, as Ersted calls them, may, he thinks, be also arranged in a series beginning with those bodies which possess the character of alkalinity in the greatest perfection, and terminating with those which are most completely acid. Of course the bodies in the middle of the series possess but little either of alkalinity or acidity, or in other words, combine with little energy either with acids or alkalies; but are notwithstanding capable of entering into combination with both. An acid, of course, is a body capable of combining with, and of neutralizing the properties of, alkalies; while an alkali or a base is a body capable of uniting with, and neutralizing the properties of, an acid. This was the definition given long ago of these bodies by Sir Isaac Newton. It is the notion adopted by Berthollet in his Chemical Statics. It is the opinion of Ersted, and is the only opinion which the present state of our knowledge will admit. Of course bodies of this series are capable of uniting with each other, and those at the two extremities of the series unite with most energy. affinities which they exert are of a peculiar kind. They have been more studied than any other department of chemistry. The compounds which they form are usually called salts.

The

The third series of M. Ersted consists of those bodies which I have distinguished by the name of secondary compounds, and to which he is satisfied with giving the name of salts.

Thus Ersted divides chemical bodies into simple primary compounds and secondary compounds; and he thinks that the bodies belonging to each may be disposed in a regular series,

In the first series there are many ductile bodies; in the second and third series there are none.

Most bodies in the first series are opaque; most of those in the two others are transparent.

Those belonging to the second class are (with a few exceptions) much less fusible than those of the first class, and at the same time much harder. Those of the third class are much less fusible than we should expect from the fusibility of their constituents, especially when composed of the most energetic acids and alkalies.

The bodies of the first class are usually good conductors of electricity. Those of the second class are almost all bad conductors while they remain solid, but become better when reduced to a state of liquidity; though not so good as those of the first class. Those of the third class are all bad conductors while solid; but when they contain much water, they acquire the property of conducting electricity.

The most astonishing of all the forces which produce the chemical effects is fine. The kind of combustion which has been hitherto almost exclusively studied by chemists, is that which results from the union of a burning body with oxygen. To express the cause of this phenomenon, we say that the combustible body has an affinity for oxygen; and that oxygen has an affinity for the burning body. After a body has burned for a certain time, it loses its faculty of burning any more in the same circumstances. This change is expressed by saying, that the body is saturated with oxygen. This phrase means merely that the attraction of the combustible substance for oxygen has become so weak that it is no longer capable of overcoming the forces opposed to it. But in more favourable circumstances, the combustion of the same body may proceed further. Even in this case, it would find a limit; and the same thing would take place in every supposed situation, till at last the property of burning in the body would be completely destroyed. From this we learn, that the attraction of the burning body for oxygen is weakened or even annihilated by an activity which exists in the oxygen. In the same way the attraction of the oxygen for the burning body is destroyed by an activity residing in the burning body. Thus these two forces (that in the oxygen and that in the burning body) have the property of mutually neutralizing each other. In many cases the neutralization is so complete that we can neither detect in the compound the property of burning, nor that of supporting combustion. Now in physics, those forces which mutually destroy each other are called opposite forces. The same mode of speaking ought to be introduced into chemistry: the attraction of combustible bodies for supporters is not the only common property which they possess; there are several others which disappear and reappear along with this attraction. Thus the property of acquiring electricity by contact with conductors, that of uniting with other combustibles, and that of acting strongly upon light, may be mentioned as instances. If we were to explain these phenomena by saying that they depend upon the attraction of the burning body for oxygen, we should not express every thing which results from the nature of a combustible body. We shall, therefore, call this property combustibility, and the activity which distinguishes it the force of combustibility. For the same reason the attraction of oxygen for combustible bodies, and all similar attractions, may be called the burning force (force comburente).

Combustion then is produced by the mutual attraction which exists between the burning force and the force of combustibility, forces which have the property of destroying each other, and which for that reason ought to be called opposite forces.

The combination of bodies with oxygen is not only accompa

nied by a suppression of forces, but the compounds pass into another class, and exercise another series of affinities. Some of these compounds become alkalies; while others become acids. Now the alkalies and acids are capable of neutralizing each other; and, therefore, possess opposite forces. It may, at first sight, appear unaccountable that the same operation should produce two kinds of forces quite opposite to each other. M. Ersted is led to what he considers as the true explanation by the following facts:

1. All those bodies that become strong alkalies by combustion have the property of decomposing water and depriving it of its oxygen. Such bodies must of course possess a great degree of combustibility. But all the bodies that become acid by combustion have little action on water, unless favoured by peculiar circumstances. They are, however, oxidized in the air with the greatest facility, and this oxidizement is singularly promoted by heat.

2. Those bodies that become alkaline unite with only a small quantity of oxygen, while those that become acid unite with a great quantity of that substance.

3. Those oxides which possess alkalinity in the greatest perfection are not saturated with oxygen. Those saturated oxides that combine with acids are capable of being separated from acids by much weaker forces than the non-saturated oxides. In the oxides of bodies moderately combustible, and which are not combined with much oxygen, we see acidity and alkalinity existing at once. Very combustible bodies saturated with oxygen form compounds (water for example) neither acid nor alkaline.

From the consideration of these facts, M. Ersted concludes, that those products of combustion which still possess an excess of the force of combustibility are alkaline; while those in which that force is perfectly destroyed, and in which the burning force, on the contrary, is in excess, are acid. In a certain state of equilibrium of these forces there is an equilibrium of acidity and alkalinity. But our author is of opinion that we must not merely attend to this state of the forces, but take into consideration that the forces by the effect of combustion are brought into a state of activity quite new; for the force of combustibility no longer acts as such in the alkalies, nor the burning force in the acids. Sometimes indeed we see both kinds of forces in the same substance, Thus in ammonia we find both combustibility and alkalinity existing together, and in nitric acid we have an example of the burning force and acidity in the same substance. In some saturated oxides where the burning force of the oxygen is but little restrained by the contrary attraction, we see it exhibiting almost all its force, and yet the oxide exhibits no signs of acidity. We have an example of this in the peroxides of lead and manganese, One of the forces ought then to be limited,

and (to speak so) reduced to an inferior power by the action of the other before it can produce either alkalinity or acidity.

I shall not enter into our author's observations on the intensity and capacity of acids and alkalies, because this part of the subject has been much simplified by the improvements introduced into the atomic theory since the work under review was published.

(To be continued.)

ARTICLE VII.

Proceedings of Philosophical Societies.

ROYAL SOCIETY.

April 1.-A paper, by Dr. Brinkley, was read, entitled "Results of Observations made at Trinity College, Dublin, for determining the Obliquity of the Ecliptic, and the Maximum of the Aberration of Light." After some general observations upon the obliquity of the Ecliptic, the author proceeded to consider the opinion of astronomers that observations of the winter solstice have given a less obliquity than those of the summeran opinion sanctioned by the observations of Maskelyne, Arago, and Pond; but questioned by Bradley. Dr. Brinkley referred this difference to some unknown modification of refraction, and stated that he has observed that at the winter solstice the irregularity of refraction from the sun is greater than from the stars at the same zenith distance; whence he inferred the necessity of paying greater attention to the observations made at the winter solstice. The author next alluded to the maximum of the aberration of light, which he stated, from observations made by him during the last year, to be 20·80′′.

At this meeting also, a paper, by Sir E. Home, was read, entiAed" Some additional Remarks on the Skeleton of the Proteorrhachius." The author commenced by stating, that having previously proved that this animal has four legs, and that its progressive motion through water is similar to that of fishes, he was led to look for its place in the scale of beings between amphibia and fishes. He found the vertebræ of the proteus cupped at both extremities, like those of the fossil animal; and from this and other circumstances it appeared, that the fossil animal was nearly allied to the proteus; but the capacity of the chest, and the want of sufficient room between the occiput and first rib, seemed to show that it breathed by lungs only and did not possess gills. From this circumstance, and from its appearing to have been capable of the two kinds of progressive motion, the author gave it the name of proteorrhachius.

Another paper was likewise read at this meeting, on some

new methods of investigating the sums of several classes of infinite series, by C. Babbage, Esq. From the nature of the subject, this paper did not admit of being read in detail. But the object of the author appears to have been to explain two methods of finding the sums of a variety of infinite series. One of these was discovered several years ago; but finding that some of the results to which it led were erroneous, he did not then publish it. On inquiring into the cause of these errors, he detected the second method. The cause of the fallacy was afterwards discovered, and a rule was proposed for judging of the truth of the results, and a mode of correcting them when found to be erroneous. The author stated that nearly similar results were found by MM. Poisson and Lagrange, but that neither of these mathematicians had explained the cause of the error, or given a method of correcting them.

The Society adjourned till after Easter.

GEOLOGICAL SOCIETY.

Jan. 15.-A paper was read, from S. Babington, Esq. “On the Geology of the Country between Tellichery and Madras."

The face of the country in general below the ghauts is marked by low rounded hills, composed of a porous substance called, by Buchanan, laterite. The mountains denominated ghauts, and the other mountains traversed in the course of his journey, the author describes as consisting of granite, gneiss, mica slate, &c. varieties of horneblende rock sometimes containing garnet, and in one place cyanite. The Carnatic, or country east of the eastern ghauts, is flat, as though it had been once covered by the sea; and in digging a well about two miles from the coast, a stratum of brown clay was first cut through to the depth of about five feet, then a stratum of bluish black clay nearly 30 feet, containing beds of oyster, cockle, and other shells; and at about 37 feet from the surface water is obtained.

Feb. 19.-A paper was read from the Hon. W. I. H.F.Strangways, on the Rapids of Imatra on the Voxa river, in Carelia, N.W. of St. Petersburgh, with an outline of the probable history of their formation, and a notice of the bursting of the lake Loubando into the Ladoga in 1818.

The greater part of the course of the Voxa may be considered rather as a chain of lakes than a river; near Imatra it is contracted into a narrow channel within rocky banks, about 60 feet in breadth, which continues about 500 yards; the eastern bank is a section of a table land of inconsiderable extent, deeply channelled and covered with pebbles and bolders of great size, some of which are hollowed into the most fanciful shapes. The river rushes with great fury and a tremendous noise through this channel; the rock through which it passes is the common red granite of Finland, which is easily disintegrated by mere exposure to the weather, and hence may have presented no