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of the laws of electro-magnetism to astronomical purposes.

The Americans were among the first to apply them to determine the difference of longitude at various places. The most interesting object in this department of electricity was Professor Bond's astronomical clock and chronograph, which were used for ascertaining, in connection with the Atlantic Telegraph Cable, the difference of longitude between Newfoundland and Valentia. The apparatus of this clock and chronograph are so contrived, that the precise epoch of an observation can be registered to the one-fiftieth part of a second. Such is the wonderful accuracy of observation to which modern science has attained. As appertaining to this apparatus, Sir W. Thomson's ingenious electro-dynamometer inay be noticed, which was exhibited by Messrs. Elliott. Sir W. Thomson has been long engaged in perfecting this instrument, which was of signal use in laying the Atlantic Telegraph Cable; and he has lately constructed one of such delicacy, as to be capable of measuring differences of potential, ranging from one-fourhundredth of a Daniell’s cell up to 100,000 cells.

The best chronoscopes and chronographs were exhibited by France. The principal use of these instruments is to determine the velocity of projectiles by electricity, and to register the precise time at which an astronomical observation is made. Those constructed by E. Hardy for the French Government are admirable specimens of mechanical ingenuity.

A very clever contrivance for engraving by electricity was exhibited in the machinery department. A metal plate, having the design which is to be engraved drawn on it with a particular kind of ink, is slowly rotated, while several other plates, on which the design is to be engraved, are also slowly rotated. The engraving is the effected by applying a diamond cutting point to the face of each plate, which is pressed against it, through the agency of an electrical current, whenever a blunt point presented to the first plate encounters the ink, but is withdrawn at other times. The point presented to the first plate is a feeler which determines by electrical agency whether there is ink beneath it or not. If there is, the diamond points opposite to all the other plates are pressed in ; if there is not, they are withdrawri, and do not act.

A new and powerful electrical machine was exhibited by P. Töpler, of Riga. It acts on the principle of multiplying induction resulting from a series of glass parallel discs rotating rapidly. The sparks produced by this machine are very numerous and powerful. France exhibited a great variety of magnificent magneto-electric apparatus, constructed for the Ecole Polytechnique by Nollett and Ruhmkorff. The best application of electricity for the production of electric light was exhibited by M. Serrin, whose electric lamps for lighthouses are now in general use in France. This light is so intense, that it has been used with great success to obtain photographs of the catacombs under Paris. The applications of electricity to telegraphy and horology were well represented, but they were not included in the department of philosophical instruments. A whimsical application of magneto-electricity was exhibited by Trouvé, of Paris, in the form of various quaint figures, mounted as pins, etc., which are set in motion by miniature electro-magnetic apparatus.

The beautiful and interesting phenomena of diffraction and polarization have caused many ingenious contrivances to be invented for their display and examination. By far the best and most complete polarising apparatus was that exhibited by Duboscq and Bertaud, of Paris.

One of the most interesting novelties in philosophical in. struments is the spectroscope, which has made us acquainted with several new metals, and to a great extent with the solar photosphere. The startling success that has attended these pbilosophical investigations has led to the spectroscope being greatly improved. Extremely fine instruments of this description were exhibited by France. The most remarkable in all respects was that shown by Duboscq. The beam in this instrument is successively transmitted through six prisms of sixty degrees, by which means the separation of the bands of the spectrum is greatly increased. By an ingenious contrivance these prisms can be easily moved in combination.

The recent exhibition, like that of 1802, has been very complete in its display of microscopes, accessory apparatus, and objects. It is gratifying to be able to record that our country maintaimed its pre-eminence in these valuable instruments. The microscopes of Messrs. Beck, T. Ross, and Dallmeyer were found, on trial, to be the best exhibited. As was to be expected, the binocular microscope is gaining rapidly in estimation. The principle generally adopted is that of Mr. Wenham's, admirable specimens of which were exhibited by several makers. While willingly testifying to the great excellence of our English microscopes, it is very satisfactory to be able to add that the microscopes exhibited by continental makers were in all respects superior to those exhibited by the same makers in 1862. The microscopes of M. Hartnack, of Paris, were especially good.

It is remarkable that the continent, and especially France, should not have shone in the late Exhibition in calculating machines. Pascal, with whose name unwarrantable use has lately been made with respect to the forged letters attributed to him, invented an arithmetical machine; and Leibnitz in

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vented another, of a more complicated kind. But although several extremely ingenious calculating machines have been constructed since that period, the only machine of the kind in Paris was that exhibited by C. Thomas, of Colmar, which multiplies 8 figures by 8 in eighteen seconds; divides 16 figures by 8 in twenty-four seconds; and extracts the square root of 16 figures in ninety seconds. The price of this machine was £20. It is to be regretted that a specimen of the extremely beautiful calculating machine invented by the Messrs. Scheutz, of Stockholm, was not exhibited. One of these machines is employed in calculating a new life table in the Registrar General's office in London, and simultaneously prints the results.

It would greatly exceed our limits to even briefly notice the numerous objects falling under the head of miscellaneous philosophical instruments. A few, however, are too important to be omitted. Among them may be classed Lissajous' and Desain's apparatus for representing acoustic vibrations optically and graphically, exhibited by the maker, M. Kønig. This apparatus is the most perfect that has been devised for demonstrating the various combinations of rapid vibratory movements. Many other beautiful and novel acoustical instruments were exhibited by M. Kænig, who has been for many years engaged with great success in investigating the laws of sound.

The collection of spectacles by continental makers was extremely large; but as the eminent British makers of these useful articles did not exhibit, no comparison can be instituted between them and the former. How much machinery has done to reduce the price of spectacles is apparent by the fact that the house of Morey, Baillet, and Co. manufacture excellent spectacles, in good steel frames, which are sold at 2s. 6d. the dozen pair. In nearly all the spectacles exhibited provision has been made to enable the axis of each eye to coincide with the central spot of the lens, without which arrangement spectacles must be always defective.

In the department of philosophical instruments, the Paris Exhibition contained a great variety of models of machines, drawings for teaching the physical, natural, and musical sciences, anatomical preparations, etc. With scarcely an exception, all these were contributed by continental countries, the governments of which are far more disposed to afford facilities for technological instruction than that of our own. The objects of this nature exhibited by France, Belgium, Prussia, Italy, and Russia, were admirably adapted for the above purpose. There was a very interesting exhibition in the department of anatomy, by Dr. Brunetti, of Padua, who has discovered a process by which, in thirty hours, he can VOL. XII.—NO. VI.

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preserve the human and other bodies. The preparations are life-size, and so little changed by the process, that they can be used for anatomical purposes, nor are they affected by time or insects. A comunittee of the Paris Academy of Sciences has been appointed to examine and report on Dr. Brunetti's invention, with the view of purchasing the secret of his process, should it be found to be valuable.

In conclusion, we may remark, that although no just comparison can be made between the merits of foreign philosophical instrument makers and those of our own country, in consequence of the absence from the Exhibition of many of our most eminent makers, there is no doubt that in this depariment, as well as in many others, continental nations show great progress. We have, indeed, only to examine the foreigt mechanical products to be made aware that the excellent and comprehensive practical education afforded throughout the greater part of the continent, and especially in Prussia, has already borne valuable fruit; and if we desire to keep up in the race of progress, we must be at more pains to disseminate technological education among skilled artisans.

The philosophical instruments lately exhibited in Paris were not, it is true, remarkable for any great novelty, but they were highly remarkable for their general excellence; and this was often to be found in instruments made in conntries which a few years ago did not produce an orainary barometer. It was also a very noticeable feature that the foreign ipetraments are much more moderate in price than the English, which is principally due to the lower rate of wages paid to continental workmen.

To the philanthropist who desires to see the advance of mankind, this progress is extremely gratifying. « The introduction of noble inventions,” says Lord Bacon, “ seems to hold by far the most exalted place among all human actions. This,” he adds, “was the judgment of the ancients, who accorded divine honours to inventors.” And by the improvement of existing, and construction of new philosophical instruments, we have every reason to believe that the prosperity and happiness of the great family of mankind is largely advanced.

LUNAR SKETCHES.-TRANSITS OF JUPITER'S

SATELLITES.-OCCULTATIONS.

BY THE REV. T. W. WEBB, A.M., F.R.A.S.

IN our last number we gave the commencement of a few original rough sketches of the lunar surface in the neighbourhood of Eratosthenes and Copernicus, as a small contribution to the materials which in great measure yet remain to be collected for future comparison and study. We now propose to continue our remarks upon the same interesting region,

Eratosthenes.—The following notices may be referred to, concerning this crater.

1856. Jan. 15. 3, 6-inch achrom. “One-third of ring faintly enlightened beyond terminator, and just connected with it by a dimly lighted ascent,” showing that the ground in the neighbourhood of this great eruption had been upheaved like that round Copernicus, though in a much less conspicuous degree.1861. April 18. 51-in, achrom. Terminator through Tycho (48) and Fontenelle (N. of Plato, 38). “The wall a grand sight in itself. Its N.W., W., and S. slopes to a considerable distance are most curiously roughened with small hillocks and ridges, whose general direction is concentric with the wall, and whose appearance bespeaks a former semi-fluid condition," as, perhaps it might have been added, their arrangement would rather suggest the ejection of blocks than the flow of lava. Such ideas, however, can only acquire weight from extended observation.—That the surface hues in and around it are of a decided character appears from the following notices. 1864. Aug. 13. 51-in. achr. “ The wall still casts a penumbra on each side, yet the interior begins to show local colour.” Aug. 15. (1d. 16h. before Full.) “ Penumbra gone ; a strange mixture of light and duskiness on its site.” How these shadowings are arranged will appear, to some slight degree, from the two following entries, which I quote just as they stand, having given no further attention to the region, and being at present unable to examine how far they admit of being reconciled. 1864. July 22. (3d. 17h. after Full.) 53-in. achr. Eratosthenes has its E. side filled with a dark lake, or rather, two such spots joined by a narrower neck : a small dusky spot lies also at the W. foot of the central hill.” 1867. Nov. 8. (3d. before Full.) 9:;-in. silvered “ With " mirror. Eratosthenes now all in local colour; from point of junction of Apennines round the E. semicircle, the outside glacis of wall shows a curious dark grey border. This is penetrated in two places by the streaks of Copernicus, which extend perhaps (but qu?) across Eratosthenes

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