Exhibition was excellent. The great desideratum of attaching an effective artificial horizon when the sea-line is obscured, may be said to have been attained. Eminent makers of optical instruments will always supply a good and reliable sextant; but we may observe that no English mariner need now go to sea in doubt respecting the performance of his sextant, as the British Association for the Advancement of Science have organized measures by means of which sextants can be efficiently tested at the Kew Observatory.

The surveying instruments exhibited were greatly superior to those at the Exhibition of 1862. With the theodolite, which is certainly the fittest instrument for measuring terrestrial angles with precision, and which has displaced the separating circle on the continent, very great pains have been taken to obtain precision with compactness. The theodolites exhibited by London, Paris, Berlin, and Vienna makers were admirable, as also were those shown by J. Kern of Aarau in Switzerland, who employs many hundred hands in making these and other instruments. The Industrial Institution of Lisbon also exhibited several wellmade theodolites. A very ingenious stenographic and orthographic machine was exhibited by Cavaliere Rossi of Rome, with which he has made a very trustworthy survey of the catacombs under and around that city. A very good display of telemeters and planimeters was made by France and Prussia, both of which nations have used these instruments extensively in field operations during war.

A very large display by various countries was made of mathematical and drawing instruments. Those exhibited by Elliott Brothers, maintain in all respects the high character of their house. Excellent instruments of this description were also exhibited by Gravet-Tavernier of Paris, J. Kern of Aarau, and Haff of Munich. The extremely low price of the instruments by these makers, as compared with those made in England is very remarkable. The Swiss and Bavarian makers sell a magazine case of excellent instruments containing a beam compass, proportional compass, six pairs of ordinary compasses of various dimensions, several excellent drawing pens, graduated rulers, sectors and protractors, all in electrum metal, for £3188. The United States of America, which formerly imported nearly all their dividing-engines and mathematical instruments, now manufacture largely and well. The instruments exhibited by Darling, Browne, and Sharpe, of the above country, are admirable. The accuracy of their steel straight-edges is very great, and the divisions on all their scales, which are effected by machinery, are extremely clear and accurate. These articles are manufactured very largely for the engineering establishments of the United States, and also for the English market.

Several excellent cathetometers were exhibited. The most delicate were those made by Bauer, of St. Petersburg, under the direction of Professor Jacobi, and by Perreaux and Guillemot of Paris. These instruments show with great accuracy the distance between two points in a vertical line to the 0.0002 of an inch. A pantograph contrived by M. Gavard of Paris, who has long been engaged in perfecting this instrument, was highly deserving of notice for the new application that it involves. By its means duplicate figures can be engraved on several copper cylinders, and impressions taken from them. The invention is likely to be introduced in the calico printing trade.

The great attention devoted during recent years to meteorology has led to considerable improvements in instruments for registering meteorological phenomena. The exhibition of these in Paris was very complete, comprising a great variety of barometers, thermometers, anemometers, rain-gauges, etc. By far the most important exhibition in this department was that by Padre Secchi, Director of the Observatory in the Collegio Romano, who showed his automatic meteorological apparatus, invented, and almost entirely constructed, by himself. This, which is by far the best apparatus of the kind in existence, registers, by means of curves traced on paper, the temperature, pressure of the atmosphere, direction and force of the wind, amount of rain, and humidity. The apparatus, which is acted on by clockwork and voltaic currents, performs admirably, and its registrations are worthy of the greatest confidence. The construction of this elaborate and highly ingenious apparatus is most creditable to Padre Secchi; and the more so, as he derives very little assistance from Government funds. A new barometer was exhibited by the inventor, Mr. Clum, of the United States. He has called it the Aëlloscope Barometer, from aeλλa, storm, and σкоже, to view; its object being to indicate the powerful atmospheric vibrations which precede storms. It is certainly extremely sensitive, but so complicated and costly, that it is not at all likely to come into general use. The lowest price of this instrument is 1000 dollars. A new mercurial barometer, of a very sensitive nature, and extremely portable, was exhibited by Messrs. Beck. It has been tested to a height of 14,000 feet, and found to be extremely accurate.

The Aneroid Barometer,* which has become a very trust*This instrument was invented by Conté (known for the drawing-chalks which bear his name), when he was director of the Aerostatic Establishment at Meudon, founded by the first Napoleon for campaigning purposes. Conté was desirous to make a barometer that should be smaller and less liable to injury, than the usual mercurial instrument; but though he constructed that now known as the Aneroid, he was not able to make it sufficiently precise to be depended upon, and thus left it for Vidi and others to perfect it.

worthy instrument, has, in the hands principally of Naudet, of Paris, been still further improved, and especially those intended for pocket use. Bourdon's metallic barometers, composed of coiled tubes exhausted of air, and hermetically sealed, have also been considerably improved, principally by Richard, of Paris, who states that they now require no correction.

A great variety of excellent thermometers were exhibited, principally by foreign makers. No important improvement was, however, apparent. Those made by Reverend, of Paris, are remarkable for their clear and well-cut graduations. Mr. Bache, of the United States, exhibited a deep-sea thermometer of novel construction, for registering the temperature by the action of metal bars. M. Bréguet's metallic thermometer has been further improved, so as to render it more sensitive. This instrument has been lately used by Mr. Wheatstone, in connection with his invention for ascertaining the temperature at distant places by telegraphy. By means of magnets and connecting wires, a Bréguet thermometer, placed on the summit of Mont Blanc, can be read off at Chamouni, or the temperature at great depths in the earth or ocean ascertained in the same manner at any moment.

Electricity, and especially electro-magnetism, was largely illustrated. The apparently inexhaustible applications of this mysterious force are continually taxing the inventive power of man. The grand desideratum, however, of obtaining a motive force which shall supersede that of steam has not yet been discovered, the few machines of this nature in the Exhibition being at once weak and costly. The great mechanical difficulty which prevents the application of electro-magnetism as motive power in prime movers is the short distance through which the action of magnetism extends. This has been sought to be overcome by calling into action, seriatim, a number of electromagnets. It is possible by this means to work a crank of one or two inches in length with sufficient power to turn a small lathe; but it admits of easy demonstration that an electrical machine, with zinc for its fuel and acid to burn it, cannot be made to rival steam-engines.

Mr. W. Ladd exhibited a very ingenious and energetic electro-magnetic machine, embracing the new principle of augmenting indefinitely the power of an electro-magnet by currents produced by itself. The apparatus can be employed for lighthouses, or other purposes. It is driven by a one-horse power steam engine, by which force effects are produced quite equal to a fifty Grove's battery.*

Very beautiful illustrations were exhibited of the application *Mr. Saxby has lately discovered that by passing electro-magnetic currents through masses of iron, internal flaws in the iron can be unfailingly detected.

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 may 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 then 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 withdrawn, 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. Franco 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-clectricity 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 instruments is the spectroscope, which has made us acquainted with several new metals, and to a great extent with the sclar photosphere. The startling success that has attended these philosophical 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 1862, 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