to circumstances, and which finally is of such whiteness as not visibly to alter the color of organic tissues illuminated by it. This problem has just been solved by Dr. Fonssagrive, physician of the naval school at Brest, with the coöperation of Messrs. Ruhmkorff and DuMoncel. The apparatus consists of an empty tube of Geissler, of very small diameter folded and turned upon itself after the manner of multipliers; this tube contains a gaseous mixture which gives a perfectly white light when it is traversed by an electric current produced by an induction coil.

Phosphorescence. The electric lamp (photophore) of which we were just speaking calls to mind some observations upon phosphorescence which have just been made by Phipson; he has found that like cane sugar, the sugar of milk or lactine becomes luminous by concussion, and also by fracture. To evolve phosphorescence from the nitrate of uranium, it is sufficient to shake briskly a bottle containing a certain quantity of this salt in the crystalline state. The light is very vivid when the experiment is made with one or two kilograms of this substance. Calomel possesses the same property, although in a less degree.

Works of Arago.-The sixteenth and last volume of Arago's works has just appeared. It contains a great number of unpublished researches made by Arago during his career.

The sixteen triangles are here given which Messrs. Biot and Arago determined in the prolongation of the meridian of France to the island of Formentera. Arago alone, has measured besides, a seventeenth triangle having its summit at the enclosure of Galaro in the island of Majorca and resting in one direction upon Camprey in the island of Trizza, and the other upon the mole of Formentera, with the design of obtaining the length of an arc of the parallel nearly 3° from the extremity of the meridian, and to determine the curvature of that portion of the earth's surface. The results of these measurements, heretofore unpublished, are found in this volume.

Arago in the year 1853, the very year of his death, communicated to the Academy a memoir upon the figure and physical constitution of Mars, which is likewise contained in this volume, and is accompanied by more than 3000 micrometrical measurements of the diameters of Mars, Jupiter, Saturn and Uranus, which were taken from 1811-1847.

It is well known that Arago made numerous investigations in regard to the refractive power of atmospheric air, dry or humid, and of different gases and vapors. He labored in this department for nearly half a century, namely, in 1805 with Biot, in 1815 and 1816 with Petit, and in 1852 with Fizeau. Chemists and physicists will derive much advantage from the determination of the refractive powers not only of some simple gases, but also of compound gases such as oxyd of carbon, carburetted hydrogen, sulphuretted hydrogen, cyanogen, the vapors of sulphur and of carbon, of sulphuric ether and chlorohydric ether.

This volume also contains studies upon optics, atmospheric electricity, &c. United to the other fifteen volumes it forms a lofty monument to science as well as to one of its most noble representatives.

Bibliography. The following works have just appeared at Paris.

Oeuvres d'Arago, Tom. xvi, 1859; chez Gide, 5 rue Bonaparte.-This volume is devoted to scientific notices bearing upon the personal labors of Arago, many of which have never before been published.

At the Librarie centrale des sciences rue de Seine; Recherches sur le non-homogénéité de l'étincelle d'induction, par M. TH. DU MONCEL, 1860.-M. du Moncel, who gives all his leisure to the study of electricity and its applications, presents in this brochure the result of his researches upon the electric spark, and especially the spark of induction, of which the non homogeneity was discovered by him in 1855. At Baillière Bros., Paris & New York. Traité elementaire de Physique expérimen tale, Tom. 1. 12°, 1860, par M. FORTHOMME, professor of Physics at the Lyceum in Nancy. This work, even by the confession of the author, contains nothing new, but is distinguished by its method. The most difficult questions in regard to gravity, hydrostatics and heat are explained in the first volume with great clearness, and thus rendered intelligible to persons little versed in these matters, which are so important in our day and have so many useful applications.

By Lacroix & Baudry, Quai Malaquais.—Grands hommes et grandes choses, notices scientifiques sur les inventions et sur les decouvertes modernes et sur les auteurs, par Victor Meunier. 8°, 1860-This work appears by numbers, once a week; its author, of whom we have often spoken, has acquired in France a great reputation as a popularizer. He established the Ami des Sciences, a journal for scientific discussions, which he has directed for six years, and is remarkable for the independence of his opinions and judgments. M. V. Meunier in this new publication proposes all the great scientific questions of the day.

ART. XXXVIII.-Description of an Equatorial recently erected at Hopefield Observatory, Haddenham, Bucks; by the Rev. W. R.

DAWES.

(From the Monthly Notices of the Royal Astronomical Society.)

My observatory was furnished, in May last, with an equatorially-mounted telescope by Messrs. Alvan Clark and Sons, of Boston, U. S., which in several important points differs from any other in this country; and I therefore hope that a brief description of it may not prove uninteresting to the Royal Astronomical Society.

The form combines great firmness and compactness with considerable elegance of design. The massive part of its structure is of cast-iron, the base of which is firmly bolted down to a stone pier. The semicircular form of the upper part affords a secure position for most of the wheel-work of the driving-clock, of which the going-weight descends in a groove on the east side of the pier, and is not seen in the drawing. The space between the polar axis and the semicircular bed-piece is occupied at its lower part by the hour-circle. Immediately above this is a sector, which clamps on to the axis, and the wheel-work of the clock occupies the upper portion. The sector has a radius of rather more than 9 inches and an arc of 30°, or two hours of right ascension. This arc has a face of an inch and a half in breadth, between which and a cylinder 7 inches in circumference there is just room enough for two thin bands of sheet-brass, each of about three-fourths of an inch in width, to pass side by side. These bands are both keyed by the end into one groove in the cylinder, at such a distance that they cannot overlap or interfere with each other. They are then bent round the cylinder in

opposite directions, the end of one being fastened to one extremity of the arc of the sector, and the end of the other at the other extremity of the arc to a piece of brass which is acted upon by a screw and nut, for giving to both the bands a due degree of tension. The sector and cylinder thus move together without friction, irregularity, or lost time.

Upon the same arbor with the cylinder is the wheel, 15 inches in circumference, in the racked edge of which the driving-screw works. This arrangement gives the screw about the same driving power as if it acted on the edge of a wheel nearly 40 inches in diameter, fixed on the polar axis.

I have every reason to be satisfied with the going of the driving-clock; and the cylindrical bob of the pendulum being screwed on to its steel rod, the rate is capable of adjustment to the greatest nicety. Great care has been bestowed by the makers upon the accurate dividing of the wheel-work; and I have much pleasure in acknowledging that its performance fully bears out my expectations, founded on the character given by the Messrs. Bond of the clock-work applied by the same makers to the great Munich equatorial in Harvard Observatory, which has been so successfully employed for the purposes of telescopic photography. While the speed of the clock is regulated by the vibrations of the half-seconds pendulum, the action of the pendulum on the wheel-work is rendered smooth and equable by an ingenious application of Bond's Spring-governor; and so perfectly successful is this contrivance, that with the thread of the micrometer bisecting a star, and a power of 800 or 1000 on the telescope, no interruption or jerk from the escapement is perceivable.

For producing a slow motion in right ascension, the drivingscrew is mounted on a brass frame, which, being carried by a fine screw under the observer's control, acts as a slipping-piece through nearly five minutes of time.

A firm clamp, close to the cradle of the telescope, fixes the declination-axis, and is accessible to the observer both at the eye-end, and also during the setting of the declination-circle. A slow-motion screw acts on an arm extending from the clamp to the bottom of the cradle to which the screw is attached.

To permit the adjustment of the polar-axis to the latitude and meridian of the place, the upper part of the cast-iron bed-piece is made with a groove which receives loosely a projecting keel on the portion bolted down to the pier. The form both of the groove and of the keel being semicircular, the upper portion is moved upon the lower by the stout screw which is seen in the drawing, and the polar-axis is thus easily raised to the required angle. The adjustment to the meridian is performed by the screws on each side of the groove in the upper piece pressing

against the keel in the lower, which has play enough in the groove to allow of a moderate degree of azimuthal motion.

To facilitate the finding of objects in Mr. Clark's "Two-eyepiece Micrometer," when their distance exceeds the field of one of the eye-lenses, the finder is furnished at its eye-end with a small position-circle divided into degrees. The thick wires of the finder being placed in the direction of the objects to be measured, the reading of the position-circle indicates the approximate setting for the micrometer, whereby the two objects may be immediately found by their respective eye-lenses. The aperture of the finder being two inches, it will show a star of the 9 magnitude of Struve's scale.

The object-glass of the telescope has a clear aperture of 81 inches, and a focal length of about 110 inches. The materials were furnished by Chance and Co., of Birmingham. The figure is excellent to the circumference, and the dispersion but little over-corrected. Its performance fully supports the character of Mr. Alvan Clark's object-glasses, and I believe it to be capable of everything which can be performed by such an aperture. It clearly divides 72 Andromeda, and shows the smallest companions among the stars of the Pulkova Catalogue. Haddenham, near Thame, November, 1859.

SCIENTIFIC

INTELLIGENCE.

I. CHEMISTRY AND PHYSICS.

1. On Fraunhofer's Lines.-KIRCHHOFF has communicated a preliminary notice of very remarkable investigations on the spectra of colored flames. These investigations have given an unexpected clue to the origin of Fraunhofer's lines, and justify some remarkable conclusions as to the constitution of the atmosphere of the sun and perhaps also of the more brilliant fixed stars.

Fraunhofer remarked that in the spectrum of the flame of a candle there are two bright lines which correspond with the two dark lines D of the solar spectrum. The same bright lines are obtained more easily and stronger from a flame into which common salt has been introduced. The author produced a solar spectrum and allowed the sun's rays before they fell upon the slit to pass through a powerful salt flame. When the sunlight was sufficiently weakened two bright lines appeared instead of the two dark lines D; when however the intensity of the sunlight exceeded a certain limit, the two dark lines D were seen with much greater distinctness than without the presence of the salt flame.

The spectrum of Drummond's light usually contains the two bright sodium lines, when the luminous portion of the lime cylinder has not been exposed to ignition for a long time; if the lime cylinder remains fixed, the lines become weaker and finally vanish. Under these circumstances, a

salted alcohol flame placed between the lime cylinder and the slit, produces two dark lines of extraordinary sharpness and fineness, which exactly correspond to the lines D of the solar spectrum. In this manner these lines are artificially produced in a spectrum in which they do not actually occur.

If we introduce chlorid of lithium into the flame of Bunsen's gas lamp, the spectrum exhibits a very bright, sharply defined line, which lies in the middle between Fraunhofer's lines B and C. If we allow solar rays of moderate intensity to pass through the flame to the slit, we see the line bright upon a dark ground; but with a greater intensity of the sunlight a dark line occupies its place, which has precisely the character of Fraunhofer's lines. When the flame is removed, the line vanishes completely.

The author concludes from these observations that colored flames in whose spectra bright sharp lines occur, diminish the intensity of rays of the color of these lines, when these pass through them, to such a degree, that in place of the bright lines, dark ones occur, whenever a source of light of sufficient intensity is placed behind the flame. He further concludes that the dark lines of the solar spectrum which are not produced by the earth's atmosphere result from the presence in the ignited sun's atmosphere of those substances which produce in the spectrum of a flame bright lines in the same place.

We may assume that the bright lines corresponding with D in the spectrum of a flame always arise from the presence of sodium; the dark lines D in the solar spectrum allow us therefore to conclude that sodium is present in the sun's atmosphere. Brewster has found in the spectrum of the flame of saltpetre bright lines in the position of Fraunhofer's lines A, a, B; these lines indicate the presence of potassium in the sun's atmosphere. From the author's observation that no dark line in the solar spectrum corresponds to the red lithium line, it would follow that lithium is either not present at all in the sun's atmosphere or is present only in very small quantity.

The investigation of the spectra of colored flames has in this way obtained a new and high degree of interest. The author promises to pursue the subject in connection with Bunsen, and states that they have already obtained results which render it possible to determine the qualitative constitution of complicated mixtures from the appearance of the spectrum of their blowpipe flames. In pursuing together the investigation of Kirchhoff's discovery of the influence of flames upon rays of light, a remarkable fact has appeared which promises to be of great importance. Drummond's light requires a salt-flame of low temperature in order that the lines D may appear dark. The flame of alcohol and water is adapted to this purpose, but the flame of Bunsen's gas lamp is not. In this last case, the smallest perceptible quantity of salt causes the bright lines to appear. The authors reserve the developement of the consequences of this remarkable fact.-Pogg. Ann., cix, p. 148, January, 1860.

Note.-Professor Stokes, in a letter to the editors of the L. and E. Phil. Mag. directs attention to the fact that Foucault, in 1849, published a short paper in l'Institut containing observations exactly analogous to those of Kirchhoff. Foucault's experiments were made by transmitting solar light through the galvanic arc, and appear to have escaped attention until their second and independent discovery by Kirchhoff.