whole system of French triangles between Montjouy and Formentera. There is, perhaps, hardly one of his numerous and laborious works calculated to give a better idea of the extreme scrupulousness of all his proceedings, and his contempt of labor where the object is to elicit truth in its most absolute form from a mass of observations of undoubted excellence, than this last computation. A mistake, as is well known, had been committed. in one part of the computation of the French triangles, by which the total distance between the parallels of these two points had been rendered erroneous to the extent of nearly seventy toises. The mistake, however, had been rectified by the independent calculations of four eminent French geodesists, and their conclusions agreed within three or four toises of each other. This, however, did not satisfy Bessel, and he actually recalculated the whole of the work by his own method, producing a result agreeing with the mean of the four determinations alluded to within a fraction of a toise.

We are still very far from having exhausted the long catalogue of Bessel's astronomical labors. His memoir on the precession of the equinoxes, honored with a prize by the Berlin Academy, and his researches on the planetary perturbations, might well demand some especial notice, did not our necessary limits forbid it, and oblige us also to pass unmentioned, otherwise than generally, the astonishing host of contributions with which, from time to time, he enriched the periodical literature of astronomy. The greater proportion of these are contained in the Astronomische Nachrichten so great a number indeed, and many of them of such extent, that perhaps it is not exaggerating to say that at least a fifth part of that collection, (now consisting of twenty-four volumes,) has emanated from his pen. The Zeitschrift für Astronomie, the Königsberger Archiv für Naturwissenschaften, the Monathliche Correspondenz, and the Supplements to the Berlin Ephemeris, contain also many and valuable communications from him.* And when it is recollected that many of these papers are essays of great length and deep interest, abounding in profound research and new conceptions on almost every subject with which astronomers are conversant, we shall see cause to admire no less the indefatigable industry of the man than the extent and versatility of those powers which produced such a profusion of valuable matter. Some of these essays, retouched and enlarged, form part of a work entitled Astronomische Untersuchungen, or Astronomical Researches, two volumes of which have appeared, and a third was understood to be in preparation when his labors were arrested by illness.

In Poggendorff's Annalen der Physik, occur occasional communications by Bessel: among others, a long and interesting one in vol. lxxxii, (vi, N. S.,) on the adjustment of thermometers.

In the year 1842, Bessel for the first and last time, visited England, and was received in a manner befitting the high estimation in which his merits were held. His unaffected and pleasing deportment, the charm of his conversation, and the rich fund of information and instruction it afforded, will be remembered with pleasure and regret by all who had the good fortune to be in his company.

There can be little doubt that he was preparing, on his return to Germany, and perhaps even before his visit to England, for an attack upon that great problem whose solution has done so much honor to Le Verrier and Adams. He had, in fact, with a view to this undertaking, engaged a young and promising astronomer, Mr. Flemming, to reduce anew, with the utmost rigor, all known observations of Uranus, including the Königsberg observations of that planet, and to compare them with the tables. This was the groundwork of his intended researches. Mr. Flemming completed the reductions, which are in the possession of Mr. Schumacher, and died soon afterwards, and the fatal malady of which, after two years of continually increasing suffering, Bessel himself died, made its appearance, and interdicted every serious labor.

The scientific character of Bessel will have been easily collected from what has been said of particular branches of his extensive labors. One leading feature of it was the concentration of all known data on each particular subject of inquiry, with the view of expressing from them, by the highest and most refined application of mathematical and computistic power, the utmost they are capable of affording in the direction of numerical precision; and as a means to this end, to satisfy this earnest longing after precise results, an equally earnest and successful endeavor to improve to the utmost all formulæ and systems of computations as such; that is to say, to put them before the computist in a state ready for immediate use, and to give the last precision which the state of science admits to every fundamental and every derivative coefficient. In the preface to his Untersuchungen, he says of himself, that he at no time felt any especial predilection for one rather than another particular branch of astronomical occupation, but that one idea was continually present to his mindthat of always working up to an immediate and definite object; either that of arriving at some positive result, more perfect than what before had been obtained, or that of removing some acknowledged obstacle which opposed at once the improvement of more than one subject. And in this remarkable passage he goes on to declare, that the desire of merely accumulating data by observation, without the intention of using them to such ends, was altogether alien to his tastes; and that the deduction of actual results from observations, by the observer himself, with a

distinct view to the improvement of knowledge, appeared to him, at all times, an essential condition of success in all astronomical research.

As a mathematician, Bessel takes, undoubtedly, a high rank; not, indeed, as an original inventor in the abstract walks of the pure analysis, but always with a view to applications, in which, whatever occasion required its exertion, his skill was never found unequal to the task on hand, no matter what its difficulty. As a practical astronomer, his knowledge of what may be called the theory of instruments-the mode of detecting, compensating, and eliminating their errors; the influence of flexures of their limbs, tubes, and other parts; and his acquaintance with, and constant practice of, every delicacy in their use, were such as has never been surpassed. Equally great in perfecting old methods of observation and in suggesting new, the practice of the modern German school of astronomers is almost emphatically Bessel's practice; and he was deservedly looked upon as a guide and model, not only in Germany but by Europe.

Bessel was, of course, elected into almost every academy in Europe as an Associate. He became a Foreign Member of this Society in 1822. As he advanced in years and in reputation, distinctions of a different kind were conferred upon him; among others, the order of the Dannebrog by the King of Denmark, and that of the Red Eagle, with the title of "Geheimer Regierung's Rath," and the order of Civil Merit by his own sovereign, whose favor he constantly experienced, and whose attentions during his last illness were of the most benignant kind, and soothed, though they could not alleviate his sufferings.

ART. XXIII.—On the Properties of Ozone; by C. F. SCHÖNBEIN.*

By a number of experiments made by myself and repeated by others, it has been demonstrated that ozone (which I take for a peroxyd of hydrogen, and Berzelius for pure oxygen in a peculiar condition) is the most powerful oxydizing agent we at present know of. A most striking instance of its exalted chemical powers is the fact, that metallic silver being in a state of minute mechanical division and put in contact with ozone, is readily transformed into the peroxyd of the metal even at very low temperatures. The several facts I have lately ascertained, and which I am going to state, will give further proofs of that power.

* Communicated for this Journal, by Prof. Schönbein, in a letter to Prof. Silliman, dated Bâle, July 15, 1847, and received through Prof. Beck of Cambridge, Mass.

1. Ozone has the property of decomposing the protoxyd salts of manganese, throwing down that metal in the shape of the hydrate of peroxyd of manganese and setting at liberty the acids of the said salts. If aqueous solutions of sulphate, nitrate and muriate of manganese be shaken with atmospheric air which has been strongly ozonized in the usual manner, (by means of phosphorus,) ozone rapidly disappears, the saline solutions become turbid, hydrate of peroxyd of manganese is precipitated in the shape of little scales of a brownish color, and sulphuric, nitric or muriatic acid set at liberty. To cause the decomposition described, it is not required to dissolve the salts, the latter being acted upon by ozone even in their solid state. I make use of this remarkable property of ozone to prepare a specific and delicate test for that curious substance. Small strips of the whitest filtering paper are drenched with a weak solution of sulphate of protoxyd of manganese, suffered to dry, and kept in stoppered bottles.

On introducing such paper into ozonized air, it rapidly assumes a brownish tint, growing darker and darker, the longer the test paper is left suspended within the air. If the atmosphere happens to be strongly ozonized, the discoloration makes its appearance after a few seconds suspension. I hardly need mention that the test paper turns brown when exposed to the action of oxygen, which has been obtained by the electrolysis of water, and exhibits the peculiar electrical smell. The said paper may also be used to prove that ozone is formed by electrical discharges taking place either in oxygen or atmospheric air. By exposing a bit of test paper to the action of the electrical brush, (playing in air or oxygen,) it undergoes the same change of color as it does within air ozonized by phosphorus, or within the oxygen produced by electrolysing water. But as under the first mentioned circumstances, only very small quantities of ozone are generated, it requires rather a long action of the electrical brush to turn the test paper brown.

Electrical discharges continually taking place in our atmosphere, and ozone being invariably produced by them, it necessarily follows that some small portions of that oxydizing agent are present in atmospheric air. The correctness of that conclusion is most easily proved by the means of my test paper; for on being exposed to the action of free circulating air, it gradually assumes a brown tint, whilst the paper remains perfectly white, when kept inclosed within a bottle filled with atmospheric air. According to the state of the atmosphere, the test paper is comparatively more or less rapidly turned brown, but always slowly. I have strips of paper which have been very perceptibly turned brown, after a week's exposure to the open air.

SECOND SERIES, Vol. IV, No. 12.-Nov., 1847.

41

I have tried to produce images by drawing with a solution of sulphate of manganese upon paper, and exposing the latter (when dry) to the action of atmospheric air which has previously been strongly ozonized by the means of phosphorus; and I may say that I have obtained very pretty results. The drawing or writing comes out within a few minutes, first exhibiting a yellowish tint and afterwards a deep brown shade. Gaseous sulphurous acid, readily uniting with the hydrate of peroxyd of manganese to form colorless sulphate and hypo-sulphate of manganese, these manganese images or writings may be almost instantaneously destroyed by introducing them into a bottle containing some gaseous sulphurous acid. And it is a matter of course that the images thus extinguished are restored by reëxposing them to the action of ozonized air. These reactions may be used for making very pretty class-room experiments to show the action of ozone upon manganese salts, and that of sulphurous acid upon peroxyd of manganese. They will perhaps also allow of a practical application. I may add that my test paper after having been turned slightly brown by ozone serves as a test for sulphurous acid.

2. Ozone enjoying so many properties in common with chlorine and bromine, I suspected the two latter bodies would act like ozone upon the solutions of manganese salts, and found my conjecture confirmed by experiment. If aqueous chlorine or bromine is mixed up with a solution of sulphate, nitrate or muriate of manganese, a very slight action takes place in the dark, but no sooner has the mixture been exposed to the action of solar light than a reaction begins and peroxyd of manganese is thrown down.

3. Sufficient quantities of ozonized air being treated with a solution of basic acetate of lead (extractum Saturni), throw down all the excess of oxyd of lead in the shape of the brown peroxyd transforming the basic salt into a neutral one. Chlorine and bromine act in a similar manner. If aqueous chlorine or bromine be added to a solution of the subacetate mentioned, until the whole precipitate first formed has disappeared, and the mixture becomes limpid again, very soon after, the liquid will become turbid, peroxyd of lead being thrown down. To show these reactions in the most simple manner, I drench strips of white filtering paper with a solution of the subacetate and suspend them in bottles, containing some ozone, chlorine or bromine. After a certain time these strips will have assumed a brown color resulting from the peroxyd of lead formed under these cir

cumstances.

4. Ozone has the power of forming permanganic acid under the following circumstances. If the bottom of a large bottle filled with atmospheric air be covered with a solution of sulphate of manganese and a bit of phosphorus having a clean surface be placed