without explaining it. An observation which I made some years since along with one of my brothers* has directed my attention to this subject. It related to the fall of a cylindrical meteor whose position was sensibly in the plane of the magnetic meridian. Many luminous meteors have been observed in this same position or near it, if I may judge from some of those described in the catalogue of Borguslawsky.†

The special position of the meteor observed by my brother and myself was not fortuitous; it was determined by the magnetic action of the earth, an action which may be powerful in its influence on meteorites consisting essentially of the magnetic metals, iron and nickel. In our view, the terrestrial magnet, the earth, decomposed by influence the normal fluid of the meteoric mass, and so gave the meteor thus polarized the direction of a compass-needle.

In generalising from this fact, and recalling the experiment of Arago on the magnetism developed when a magnet acts upon a turning disc, we ask whether the magnetic polarity of our planet may not be due to a like cause. Considering it, as proved, that the sun is polarized magnetically like the earth, the sun will then be the inductor magnet, the agent which decomposes the magnetic fluid of the terrestrial globe; it will be to the earth, what the earth was to the meteor. This explanation does not resolve the difficulty, as it does not say whence comes the magnetic polarity of the sun. It implies the intervention of a magnet whose intensity is superior to that of the sun, acting on this last by induction, and impressing a polarity which the sun transmits to other planets of the system. It is the hypothesis reversed of the central magnet, for it places in space the magnetic mass which some physicists have supposed to exist within the earth.

The real cause of the magnetic polarity of the planets, is in my view the same for all, and Arago's experiment conducts to it in a straight line. It results even from the condition of their existence. Each star turning around a central axis, and in determinate curves, is influenced by the mass of these stars and their velocity at the circumference; in a word, the agent decomposing into two fluids the normal magnetism of the earth and the other planets, is their rotation. A geometer examining this opinion, would find, we believe, that the declination, inclination and the perturbations of the magnetic needle, are explained on this hypothesis much better than on any other.

Since my researches on circular electro-magnets and in general on bodies in rotation, I have sought much for experimental demonstration of this theory, and have now the conviction that this is impossible, as it is not possible for us while upon the earth to remove ourselves from the action of its own magnetism. Whenever a development of magnetism under the influence of rotation is observed, it is common to attribute it to the inductive action of the earth, rendered so striking by the experiments of Arago and Mr. Barlow.

Alongside of the different sources of magnetism mentioned in Trea. tises on Physics,-friction, pressure, percussion, torsion,-we should add * Poggendorff's Annalen, iv, 1.

+ See Proceedings, Brit. Assoc., 1853, Sept. 7, Report of Col. Sabine.

Sur la chute d'une bolide par M. N. Nicklès and J. Nicklès, Compt. Rend, de l'Acad., xix, 1035.

rotation, a mechanical action of equal title with the preceding, and whose effects, produced through a subdivision like that of magnetic polarity, are found grouped at the extremities of the axis in rotation; in the same manner as the poles develop at the extremities of a bar of iron when it is subjected to torsion.

Artificial magnets. For some time, permanent magnets have been made from cast iron by the aid of an electric current. The only diffi culty consists in tempering the metal. M. Florimond, Professor of Physics at Louvain, has recently given the results of some investiga. tions on this subject to the Academy of Sciences at Brussels, detailing the effects from using magnets of this kind in the construction of mag. neto-electric machines, these magnets being much more economical on account of the difference in value of cast iron and steel. The following are some of his conclusions :

1. Gray metal gives more satisfactory results than white metal, which is moreover too brittle.

2. Magnets tempered at a low red heat lose all their magnetism in twenty-four hours.

3. They retain their magnetism perfectly when tempered at a bright red heat.

The following is the method of obtaining the maximum magnetic power. The bars are heated to a red heat in a blast furnace; they are taken out, and powdered over the two faces for ths their length with the yellow prussiate of potash pulverized, and then they are plunged imme. diately into a large quantity of cold water, with violent agitation. When the bars are cooled, they are magnetized by means of a horse-shoe electro-magnet capable of lifting about 200 kilograms. The two poles of the magnet are applied at the place where the branches of the cast iron magnet become parallel; the poles are made to slide quite to the extremities of the branches, and then detached to repeat 3 or 4 times this same process of friction. After operating thus upon one of the faces, the other is subjected to the same treatment, taking care that the same poles are brought into contact with the same branches.

The poles of the bundle of cast iron magnets ought to be always kept in contact with an armature of wrought iron of a size proportional to that of the bundle. The bars of cast iron should be a little thick

er than those of steel.

Ascensional force of Balloons in water.-On the 18th of last June, Doctor Gianetti of the mineral springs of Orezza, Corsica, made an experiment with a balloon as a piece of hydrostatic apparatus, before a scientific commission. The object of his balloon was to raise objects from the bottom in deep water; and the force of it is such that with a diameter of 4 metres he was enabled to raise at least 31,000 kilograms. His experiment was made with a balloon of 50 centimeters, which raised 150 kilograms. With hydrogen a much greater effect would be obtained. But Dr. Gianetti, having a practical end in view, uses carbonic acid, which he obtained by the decomposition of a carbonate by means of an acid, at the bottom of the sea. He is now proposing to adapt to it a clock movement, which by opening or closing the facet in the top, by which the balloon is filled or emptied, shall cause it to rise or sink at will. It is also proposed to use this invention in river navi.

gation, for the passage of sand banks; the apparatus for this purpose could be secured to the sides of the vessels, and would not add a thickness of more than 2 centimeters (8 tenths of an inch).

Manufacture of Sal-Ammoniac from the residues of gas works.The Industrial Society of Mulhausen offers annually a number of prizes for inventions and improvements made during the year: and it also offers a prize to those who introduce a new branch of industry into the department of the Haut-Rhin. This last prize was taken by MM. Moerhlin and Stoll, who manufacture sal-ammoniac from the ammoniacal liquid of gas works. The main difficulty in the operation consists in separating the tar-like material which it contains. The following is the process adopted.

The ammoniacal liquid is mixed with slaked lime; then submitted to distillation in a boiler heated by steam; the parts volatilised pass into a worm, in which the larger part of the tar is deposited; the ammonia passes on into a Wolff's apparatus, where it leaves the foreign substances present, and finally is carried into cold water where it is condensed. In this state it is nearly free from its impurities; it is neutralized with chlorohydric acid and evaporated in a lead boiler. As it deposits it is withdrawn by means of a wooden rake; it is allowed to drain, and then introduced into a brick mould and subjected to strong pressure. Blocks of sal-ammoniac are thus obtained, which are dried in an oven heated by part of the heat furnished by the evaporating fur

nace.

Separation of bromine from iodine.-Balard's process, as carried on by M. H. de Luca, gives a method of recognizing traces of iodine and at the same time of separating it from bromine with which it is so often associated. It is based partly on the greater affinity of bromine for the metals and partly on the violet color which iodine communicates to sulphuret of carbon. An impure bromine is treated by potash (or carbonate of potash which may be more easily obtained pure and free from chlorine); it is evaporated and calcined, to transform the bromate into bromid; it is then neutralized by means of an acid; the liquid is put into a test tube, and a drop of sulphuret of carbon is introduced, after which a drop or two of bromine dissolved in distilled water is added; it is then agitated, and if there is iodine present, the sulphuret of cobalt is colored violet. It is colored yellow by bromine. It is important to avoid an excess of bromine, lest it form a bromid of iodine, which does not act. I have tried the process, and found it exact nearly to a tenth of a milligram of iodine.

Artificial Silicification of limestones. It is some years since M. Kuhlmann of Lille proposed to preserve pieces of sculpture, etc., by impregnating them with a solution of silicate of potash. SiO3 KO+ CO2 CaO SiO3 CaO+CO2 KO. This process has been used on a grand scale in certain parts of the cathedral Notre Dame. The architect of the cathedral reports as follows: 1, that the infiltration of silica made "sur les terrasses et contre-fort du choeur," in October, 1852, have preserved the stone from the green moss that covers stones in moist places: 2, that the gutters and flagging of limestone subjected to this process present surfaces perfectly dry, covered with a silicious crust: 3, that upon the stones so prepared, dust and spider webs are

less common than upon the stone in the ordinary state. The report also states that tender stones have been rendered hard; they have lost part of their porosity, and after being washed, they dry more rapidly than stones not silicified. The process has succeeded completely on all calcareous blocks, whether isolated or forming part of the structure, new and old.

It is not yet known how this process will act on mortars; but if successful, the silicification of an entire monument may be accomplished, and its restoration when old. The whole exterior might be thus cov ered with a thick bed of artificial silicate of lime, and a whole edifice be protected by this means from all atmospheric causes of destruction. Vitrification of Photographic pictures.-The author of this process, M. Plaut, first procured a photograph on glass covered with albumen, and subjected it gradually to a strong heat so as to redden the glass. The albumen was destroyed, and the photograph, if negative, became positive by reflection. The picture was made of pure silver which adheres quite strongly to the glass, so that it may be polished without alteration.

On exposing this glass to the action of hydrofluoric acid in vapor, an engraving of the design is obtained over parts not covered by the image formed of the silver. It may also be possible to strengthen the im age by a galvanic deposit and make a kind of plate from which engravings could be taken.

If, in place of arresting the process at a red heat, it is continued until the glass enters into fusion, the image sinks into the interior of the glass without being altered, and covers itself with a vitreous varnish. It appears like a design of great delicacy, enclosed between two plates of glass; and if positive proofs are employed, the method may be used for making pictured glass which may without doubt be colored by the ordinary processes.

Photographic Portraits on linen cloth.-The Revue Encyclopedique of the Abbé Moigno, from which we have taken the preceding note, states that the problem of making photographs on linen has been resolved. The Abbé Moigno has assisted at the operations of M. Wulff, the inventor; he says nothing of the processes, and we only know that the photographs were taken on linen covered with collodion.

Pyrogallic acid in wood vinegar.-The value of pyrogallic acid in photography gives much interest to the fact brought out by M. Pettenkofer, that it is afforded by the condensing apparatus for purifying gas obtained from the distillation of wood, an invention in which M. Pettenkofer has taken the greater part. M. Pauli is now engaged in the study of this acid. It is without doubt, says Liebig, owing to the presence of pyrogallic acid that we must attribute the preference which dyers give to wood vinegar, an acid which has not been replaced by the ordinary acetate of iron.

SCIENTIFIC INTELLIGENCE.

I. CHEMISTRY AND PHYSICS.

1. On the polarization of light by refraction through a metal.--BIOT found that two gold leaves are sufficient to polarize direct solar rays completely. Rollmann has examined the subject anew, and has em ployed the gold leaves both as a polarizing and as an analyzing arrangement. When the light is very intense, only a single leaf can be employed, as otherwise the field of view appears 100 dark. When used as an analyzer, a gold leaf shows very distinctly the colors of thin plates of gypsum, cooled glasses, &c., but these are naturally modified by the peculiar blue green color of the gold. If we allow plane polarized light to pass through an inclined gold leaf, and examine by a tourmaline in the light so transmitted a plate of calcspar cut perpendicular to the axis, we shall observe the phenomena of elliptic polari zation, when the gold leaf and the analyzer are turned to an angle of 45° with the planes of polarization. The colored rings are narrower in the first and third quadrants than in the second and fourth, the cross is converted into two hyperbolas, whose branches do not meet. When in the above experiment, we leave every thing else unchanged, and examine the calcspar with the analyzer, by means of the light reflected from the gold leaf in place of that transmitted, we observe the complementary figure such as we obtain it when we employ the transmitted light, and the tourmaline is turned through 90°. The tourmaline must be green in order to transmit the light well. Brewster's discovery of the elliptic polarization by metallic reflection is thus extended and completed.--Pogg. Ann., xc, 188.

2. Additional experiments on the internal dispersion of light.—In a lecture delivered before the Royal Institution in London, Prof. Stokes has communicated some new observations on internal dispersion, which are of much interest. In accordance with an observation of Faraday, Stokes has found that the blue flame of sulphur burning in oxygen is a source of rays which exhibit the phenomena extremely well. Letters written upon white paper with a solution of chinin, immediately become visible when illuminated with this light, particularly when it has passed through a blue glass, although they are invisible in gas light. The let ters remain visible when observed through a glass containing a thin layer of a solution of chromate of potash, but they instantly vanish when this glass is interpolated between the flame and the paper, the solution being impervious to the rays which occasion the color. The author points out in the next place the advantages which prisms and lenses of rock-crystal possess over those of glass, in experiments of this kind, inasmuch as they readily transmit the invisible rays. By employ. ing the light of the powerful galvanic battery of the royal institution, and lenses and prisms of quartz, the author obtained a spectrum six to eight times as long as the ordinary visible spectrum, and crossed from one end to the other with bright bands. The interposition of a plate of glass shortened the spectrum to a small fraction of its original length, the highly refrangible portion being entirely absorbed. The discharge SECOND SERIES, Vol. XVII, No. 49.-Jan., 1854.

16