ing the temperature and the direction-current at any partic ular depth in the ocean. It consists of a brass box, hermetically closed, and having attached to it an apparatus resembling a vane or rudder. Within this box a thermometer and a magnetic needle are contained, behind each of which is placed sensitive photographic paper, and in front of each of which is a small nitrogen vacuum tube. The box contains also a small induction coil. When the apparatus is lowered to the required depth, the rudder causes it to take a direction parallel to the current there existing, and hence a definite direction with reference to the needle within. The thermometer soon acquires the temperature of the water outside, and becomes stationary. At this instant an electric current is sent to the box, which, by means of the induction coil inside, lights up the little nitrogen tube, the violet light of which, photographically very intense, prints, in about three minutes, the position of the needle and the height of the mercury column upon the prepared paper. The current is then intermitted, the apparatus raised, the photographic tracing fixed, examined, and placed upon record.-3 B, Sept. 3, 1874, 6.

DISPERSION OF LIGHT BY PRISMS.

Dr. Eugene Block attempts, in his Inaugural Dissertation, to make some additions to the theory of the refraction of light passing through systems of prisms. He says with apparent correctness in his preface that the many occasions on which the spectral analysis is applied in every branch of science has in the last few years brought about important changes in the construction of the apparatus. The greater part of these changes have been prompted, not by theoreti cal investigations, but by experimental methods, whereby it has happened that many errors have been suffered to remain in the construction of the apparatus which may have a material and deleterious influence upon the sharpness of the spectrum. Dr. Block has therefore made careful investigation and comparison of such instruments as are now in use, and has developed the theory of the refraction of light in systems of prisms. He has extended his investigations to converging and diverging bundles of rays, as also to the influence which imperfect prisms, or the inclinations of the prisms can have upon the purity of the spectrum. Among

the theses defended by him at the close of his inaugural dissertation, we note that the Ketteler formula for dispersion is maintained by him as the most correct that is known; as also that the appearance of the aurora is dependent upon local climatic conditions.-Block's Inaugural Dissertation,

1873.

SPECTRUM DISPERSION OF GASES.

Lorenz communicates to the Royal Academy of Copenhagen an experimental and theoretical investigation into the chromatic dispersion of gases. His observations have been made by means of a small spectroscope, and were in part directed toward the constituents of the atmosphere, for which he gives the coefficients of refraction for each of the eight principal lines of the spectrum, and the necessary changes due to the moisture and temperature of the atmosphere. Pure oxygen, nitrogen, hydrogen, the vapor of water, alcohol, ether, chloroform, iodaethyl, carbon-sulphide, and ammonia are successively investigated by him in different degrees of density and temperature.-Mem. Kongel. Danske Vidensk. Selsk., Copenhagen, X., 486.

IMPROVEMENT IN SPECTROSCOPES.

Mr. Madan gives a simple method by which we may correct the curvature of the spectrum lines, a defect inherent in all spectroscopes as at present made. This curvature is due to the fact that the rays from different parts of the spectrum fall on the prism under different vertical angles. Mr. Grubb has lately proposed to correct the curvature by a method which had been already employed by Mr. Madan for more than a year past, and which consists in making the slit itself curved instead of straight, the curvature being so arranged as to neutralize the distorting effect of the prism. Mr. Madan's experience shows that the curved slits give perfectly satisfactory results, and that they may be easily adapted to any spectroscope; so that by having several such slits in succession, we may secure straight lines in the field of view for varying powers of dispersion. He finds that slits whose edges are curved to a radius of 21 centimeters, sensibly correct the distortion of a single carbon bisulphide prism, the

reflecting angle of which is 60 degrees. A slit whose radius is 10 centimeters corrects the distortion of a train of two

such prisms.

SPECTRUM APPARATUS FOR THE NEW OBSERVATORY AT

POTSDAM.

The maker of the optical apparatus for the Bothkamp Observatory has lately finished the spectrum apparatus for the new observatory at Potsdam, which probably is the most complete instrument of its kind. The maker, H. Schroeder, says of it that the apparatus consists of 21 single prisms combined into a system according to Rutherford's method, they being moved automatically and in such a way that the motion is accomplished with mathematical accuracy and with the greatest ease. This automatic movement allows of exact differential measurements with hitherto unattained accuracy, and is the first apparatus of this kind that has been constructed as an exact instrument for measuring. Accord ing to Dr. Vogel, the measurements are perfectly trustwor thy to the one-hundredth part of the interval between the double line D of sodium, the optical performance of this spectroscope being such that the sodium line is separated into nine fine lines. Almost all the principal lines of the spectrum are resolved into groups of lines, while new lines are seen among those hitherto known.-7 C, XI., 55.

THE ATMOSPHERIC LINES OF THE SOLAR SPECTRUM.

J. B. N. Hennessey, of the Trigonometrical Survey of India, communicates to the Royal Society of London a short memoir on the atmospheric lines of the solar spectrum as observed by him on the point known as Vincent's Hill, among the Himalaya Mountains, in the northwest province. of India, at an altitude above the sea of 1700 feet. His observations were made not only with an old spectroscope, as used in 1868 to 1871, but with a newer and finer instrument supplied by the Royal Society in 1872; and he publishes a map of the solar spectrum, showing the atmospheric lines as observed with the latter instrument. A comparison of the solar spectrum, as seen when the sun was within two hours of the meridian and as seen at sunset, shows the very striking changes introduced by atmospheric absorption. Thus

near the Fraunhofer lines A and B intense black lines are introduced, while others having but slightly less intensity occur near 48, 71, 81, 99, 101, and 183. Especially remarkable is the great increase of bands in the more refrangible portion of the spectrum; thus from 26 to 40, faint bands, and from 46 to 60, from 68 to 74, from 95 to 102, and 107 to 116, very decided bands appear at sunset, which are not visible at midday. Mr. Hennessey has observed sunsets to the number of about 100 since 1870, and has also noticed that during the autumn a kind of haze springs up in the horizon, growing higher and higher from day to day, and denser, forming a permanent winter bank of haze; by carefully observing the effect of this bank of haze on the solar spectrum, he has found beyond all question that as this bank rises day by day higher and higher, the corresponding sunset spectrum bands successively disappear, showing that the lines which are visible when the sun sets in the true horizon are introduced into the spectrum by reason of the greater thickness of the stratum of air traversed by the sunlight. He states that certain lines, for instance, number 813, are almost as good as a clock. This line commences to change as early as two or three o'clock P.M., and becomes an intense black stripe at the horizon. He states his conviction, also, that besides other changes in the solar light as the sun approaches the horizon, there is this peculiarity-that the rays of less refrangibility actually become visible, so that the spectrum appears to be extended toward the right hand.-Phil. Trans. Royal Soc. of London, 1875, 157.

OPTICAL NOTES BY MR. LEA.

M. Carey Lea, of Philadelphia, states that having a year ago published a train of investigations into the sensitiveness of certain substances to particular rays of light, leading to results incompatible with the late announcement by Dr. Vogel in reference to the sensitiveness of silver bromide when washed with color varnish, he has since then continued his investigations, and while on the one hand Dr. Vogel has adopted his own views, he himself on the other hand has been led to the positive conclusion that there exists no relation whatever between the color of the substances and the color of the ray to whose influence they modify the sensitiveness of the silver bromide.

METHOD OF ESTIMATING COLOR IN WATER.

Mr. King, city analyst of Edinburgh, has published in the Chemical News a method of estimating color in water for the purpose of determining the comparative turbidity of different samples. This method consists in adding to a known quantity of pure distilled water contained in a glass tube an aqueous solution of caramel of a certain strength until the tint communicated to the distilled water is found to equal that of the water under examination. The tubes he employs are made of perfectly colorless glass, fifteen inches long, and of such a diameter that when filled to within three inches of the top they will contain exactly eight ounces of water. The depth of color which the distilled water and caramel should exhibit is ascertained by adding ten grains, by volume, of solution of ammonium chloride to eight ounces of pure water, perfectly free from ammonia, in a glass tube, forming a column twelve inches long. The ammonium chloride solution should contain 3.17 grains of the salt in 10,000 grains of water. To this mixture, after proper agitation, 25 grains, by volume, of Nessler's solution are to be added; and this, after mixing, is allowed to repose for ten minutes at a temperature of 60° Fahr., when the color will form 30° of Mr. King's scale; or, in other words, 300 grains, by volume, or 30° (a degree being equal to ten grains by volume) of caramel solution, if of proper strength, will produce exactly the same depth of color when added to the same amount of distilled water (eight ounces) in a column twelve inches long. The caramel solution being thus prepared, in order to estimate the color two tubes of the dimensions stated are to be filled to within about three inches of the top, one with distilled water and the other with water to be tested. The caramel solution is then to be added to the distilled water until that is found to equal in color the water contained in the other tube. Every 10° consumed will represent 1° of color. The intensity of the color is ascertained by looking down through the length of the column.-1 A, March 25, 1875, 133.

FLUORESCENCE OF SOLUTIONS IN CASTOR-OIL.

Some coloring matter derived from woods that do not show any fluorescence when dissolved in water, alcohol, or other