by M. Camille Faure, who, following in the steps of M. Gaston Planté, had succeeded-according to M. Reynier-in devising a battery in which forty times as much electric energy may be stored up as could be done by the Planté pile, the result being that a large amount of force easily convertible into mechanical work, or adaptable for electric lighting, could be stored up in small and easily portable cells, could be transported from place to place, delivered from house to house, and that the great problem of a domestic electric lighting and power supply was thus solved.

M. Faure's secondary battery is an application of a new discovery to the very beautiful and well-known secondary pile of M. Gaston Planté, which our readers will remember consists of two plates of sheet lead separated from one another and immersed in a glass jar of diluted sulphuric acid; if these two plates are connected for a time with the terminals of a source of electricity such a dynamo-electric machine or a voltaic battery, oxidation and deoxidation take place on the two plates respectively, and after the exciting battery has been removed, the lead cell continues to give off a polarization current of electricity as long as the deoxidation and oxidation of the lead plates continue by their returning to their normal condition. It was from the first observed that secondary piles of this construction produced better results after having been charged and discharged a great many times, a fact due no doubt partly to the increase of surface produced by the roughening of the lead plates under the decomposition, but chiefly to the formation of lead peroxide in increasing quantities, which was alternately deposited and decomposed as the cell was charged by the battery and discharged by the polarization current.

M. Faure (whose name is well known in the scientific world as the inventor of the battery which bears his name, and in which the carbon element in a Bunsen's cell is made in the form of a bottle which contains the nitric acid) has recently introduced an important improvement to the Planté cell, by which its capacity is largely increased, so that an apparatus constructed upon his principle is capable of producing a much greater current than that given off by a secondary battery of the old construction and of the same size. As the capacity of a secondary battery, other things being equal, is due to the thickness of the layer of lead peroxide formed upon one of the lead plates, M. Faure conceived the idea of coating each of the plates with a thickness of red lead maintained in its place by a sheet of felt attached to the plate by means of lead

rivets. Both plates having been similarly treated they are rolled together into a spiral, the felt performing the two-fold duty of separating the plates and holding on the coating of read lead. This couple is then immersed in acid contained in a cylindrical cell of lead and connected by its electrode to the poles of a dynamo-electric machine or voltaic battery, and after having been charged and discharged two or three times, the red lead coatings of the plates are found to have undergone a change, the one having been entirely transformed into peroxide of lead, while the other has been reduced to the metallic state, and as this result must be due to the oxidation of the red lead on the one plate and the deoxidation of that on the other, it would appear that what may be called the storage capacity of the apparatus depends upon the quantity of red lead carried by the plates.

There can be no doubt that in this way electricity may be "bottled up" and "stored" to an almost unlimited extent, and in this bottledup condition can be carried in reservoirs to a distance, there to be utilized until it is exhausted, just as a reservoir of compressed air, or a coiled up spring, may be carried for any number of miles, and can be made to give out power whenever required at a distant station. All this is true enough and physically feasible, but the whole commercial success or failure of such a scheme must depend, as all commercial schemes must depend, upon its practical utility.

If electrical energy has to be conveyed from one place to another, it is a matter of small commercial importance in the abstract whether it is conveyed by means of metallic conductors or stored up in reservoirs and carried by road or rail; in this the commercial question involved being very much the same as that of the supplying of water by pipes. or by water carts. There can be no doubt, however, about which system is, save in exceptional cases, the most convenient, and unless it can be shown that the charging and transmission of storage reservoirs offers advantages upon economical grounds, or very substantial conveniences of application over the system of transmission by conductors, we cannot see that its commercial application upon a large scale can be as remunerative to its proprietors as its promoters would wish to make the public believe.

That M. Reynier should have infused an undue amount of enthusiasm into his paper read before the Société d'Encouragement was natural, considering that he was describing for the first time results far in advance of anything of the same nature than had been achieved

before, and it was perhaps pardonable that he should, for the greater. glory of the Faure battery have depreciated the capacity of that of Planté. But in justice to the latter gentleman, and also to arrive at a just appreciation of the real value of the new discovery, careful investigation and comparison between the two have to be instituted. This has been partially done by M. E. Hospitallier since M. Reynier read his paper, and the last number of our excellent conpemporary L'Electricien the results obtained are referred to, and the details of the experiments made are to be published in a succeeding number of the same periodical.

Criticising M. Reynier's paper, M. Hospitallier challenges several statements made in that communication. M. Reynier maintained that the Faure battery would give out 80 per cent. of the total power used in charging it. But as M. Hospitallier points out, under the best conditions not more than 90 per cent. of actual work can be transformed from mechanical into electrical energy by a dynamo-electric machine. M. Planté clearly demonstrated that his secondary battery could only give out 88 or 89 per cent. of the power charged into it, and as the difference between it and the Faure battery is one of degree and not of principle, it is not probable that a greater percentage than this could be obtained; possibly it would be less. Finally, a loss of 20 per cent. at least must be allowed for in converting the electrical power in the battery into mechanical force. Making allowances for all these losses it follows that the utmost useful work that can be got. from the battery is 52.5 per cent. of the energy employed in charging it, while at the present time it is easy with the ordinary system of conductors to obtain 60 per cent. Passing on to the question of the power which can be stored up in the Faure battery, M. Hospitallier makes an important statement in reply to the assertion of M. Reynier, that this battery can store up forty times as much force as the Planté battery. In conjunction with M. Frank Géraldy, M. Hospitallier has conducted a series of experiments on the Planté battery. The details of these experiments will be published shortly, but the results are given as follows in L'Electricien: "Admitting on the one hand as correct the figures given by M. Reynier, that is to say, that a Faure battery, weighing 165 lbs., can give out one horse power during one hour, and on the other hand our experiments on the Planté batteries, the storage power of the Faure batteries varies from one and a half to three times the power of the Planté, according to conditions which we

shall shortly publish. This result is very far from the forty-fold result given by M. Reynier, who obtained it no doubt from imperfect or badly-proportioned Planté batteries, and these results cannot consequently be accepted."-Engineering.

Reynier's Constant Battery.-M. Reynier has made a modification of Becquerel's hydro-electric battery, which is comparable to the nitric acid couples in energy without having their inconveniences. The zinc is plunged into a solution of caustic soda; the negative electrode, which is of copper, is depolarized by a solution of sulphate of copper, separated from the alkaline liquid by a permeable cell. The couple thus constituted is constant; its electro-motive force varies from 13 to 1.5 volts, according to the concentration of the liquids. The moderate conductibility of the liquids is modified by the addition of salts suitably chosen, and the resistance of the porous cell is reduced by making it of parchment paper, as had previously been done by F. Carré. This battery can be regenerated so readily that the inventor hopes to make it applicable with great economy to small electric motors and to lighting private apartments.-Comptes Rendus.

C.

Reversion of Photographic Images by Prolonged Illumination.-Janssen has found that photographic images may be inverted and pass from the negative to the positive state by the prolonged action of the light, which produces them. At Meudon the solar images are obtained in a time which varies, according to the state of the atmosphere and the nature of the phenomena, which are to be studied; the time is rarely greater than 15 of a second when they wish to obtain the photospheric granulations. When the photographic plates are prepared with gelatino-bromide of silver the time may be reduced to less than 20 of a second. If one of these dry plates receives the light for half a second or a second, the development brings out a positive image, with a white dise and black spots, as the sun appears through a telescope. This positive image may be as well defined as the negative image, which it has replaced. There is an intermediate time between those which give the opposite images, for which time the image is neither positive nor negative, but the plate presents a tint sensibly uniform. Similar inversions may be produced in views of landscapes by giving a sufficiently long exposure. - Compt. Rend. C.

Thermo-Dynamics of Liquid Surfaces.-Van der Mensbrugghe is still continuing his study of the application of the second law of thermo-dynamics to the variations of potential energy in liquid surfaces. He is giving special study, by means of some of the most salient facts, to the great cycle of change which embraces the evaporation of the superficial layers of ocean waters, the elevation of vapors into the atmosphere, their condensation into mists and clouds, their fall in rain or snow, the consequent production of glaciers, torrents and rivers, the circulation of water courses, and their return to the bosom of the ocean. He hopes to attract the attention of meteorologists to his investigations in order to induce new and extensive researches in the direction of his inquiries.—Bull. de l'Acad. Belg.

C.

Intermittent Luminous Signals.--In the ordinary use of lamps for light-house signals the intermittences are produced by a diaphragm which moves before the light, so that the fuel is wasted during the eclipses. At present the average waste of light is about sixty-five per cent., but if a signal was sent twice a minute, sufficient to indicate the first two letters of the light-house, there would be a waste of about ninety per cent. In order to remedy this extravagance Mercadier proposes to adopt a Dubosq lamp with a round wick and a tube in the centre of very small diameter, through which a jet of oxygen can be discharged upon the top of the wick. In spite of the high temperature of combustion, the lamp does not heat much; it consumes little petroleum, and the wick does not crust. Therefore it will operate for many days without being trimmed or filled anew. The intense flame is produced by the combustion of petroleum vapor at the centre of the jet, and the surrounding film of air being a bad conductor the lamp heats only at the top of the burner. The oxygen is enclosed in a reservoir, under suitable pressure, which in his apparatus does not exceed four millimetres (157 in.) of mercury; it first passes through a manipulator, which has a form similar to that of the key of a Morse instrument, traversing a caoutchouc tube, which is pressed together when the key is at rest. Upon depressing the key the pressure upon the tube ceases, and the oxygen reaches the flame; when the key is released the oxygen jet is stopped. In this manner the flow of oxygen is manipulated as simply as the electric current in the Morse system. The rapidity of manipulation is more than sufficient for all the requirements of optical telegraphy. A method somewhat similar has been contrived by Mercadier for the electric light.-Compt. Rend. C.