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64 THE CIVIL ENGINEER AND ARCHITECT’S JOURNAL. [February 1, 1368. practical men on this rojcl, and don’t believe in thy gimcracks.” The centre-rail machinery was accordingly taken of and melted up for castings ; and thus Mr. George Escol Sellers was deprived of the honor of having his name associated -with the first prac tical success of this invention—an honor ascribed to the inventor of the very inferior machine which is now daily hauling trains across the Alps. The day may perhaps come when the Sellers engine will in like manner cross the Rocky Mountains. In these few lines you have the entire history of the centre-rail engine in this country. Yours, &c., John C. Thautwine. . Philadelphia, Dec. 6, 1867. ♦ EXPLOSION OF AN OXYGEN RESERVOIR. An accident occurred a short time since at the Pennsylvania Hospital for the Insane, in West Philadelphia, which should be recorded, because a knowledge of this is likely to prevent similar disasters in future. In this establishment, the magic lantern, for more than twenty years under the direction of Dr. Kirkbride, Superintendent of the Institution, has been con stantly employed, and has proved itself of incalculable service in connection with the neutral treatment pursued, affording as it does an inexhaustible supply of amusement, instruction, and mental occupation, without excitement. Long before the stere opticon was known to the public at large, lanterns for dissolving views and photographic projections were familiar' in that locality. Every improvement in the lanterns and their illumination was promptly introduced, and for more than twelve years oxy gen has been constantly made, and every night consumed, without accident or injury, until November 14th, when, during the manufacture of a fresh supply, the oxygen reservoir exploded, and a thick board used to support the weights placed upon it, striking the man employed in making the gas (who was close to it) on the forehead, fractured his skull. At the request of Dr. Kirkbride, we examined the apparatus, and think that the history of this accident may be briefly stated as follows :—The oxygen was made from chlorate of potash, without oxide of manganese, in a grinding machine, the retort or pot was heated in one of the ranges of the kitchen, on the ground-floor, the outlet pipe was connected by a thick rubber hose (three- ply) with an iron tube passing through the floor, and leading into a tin gas-holder of the usual construction, in the cellar below. In this particular instance, the residue from a previous operation was, through carelessness or inadvertence, left in the retort, occupying probably about three-quarters of its capacity. When the retort was supposed to be hot enough, about a pound and a quarter of chlorate of potash was slowly ground in, but as there was no wash-bottle or other means of indication, the operator could not tell whether any of it was decomposed before the whole was introduced, and we think it extremely probable that, owing to the residue in the retort, the whole charge was introduced before any gas had been liberated ; in fact, when we examined the contents of the retort, we found a notable quantity of chlorate still remaining. Under these conditions, as all are aware, a large amount of chlorate would fuse, and then begin to liberate oxygen with violence, and it would be highly probable that sparks from dust or chips would be carried as far as the rubber tube, and ignited. We have, indeed, in our own experi ence, on three occasions, observed this very thing to happen when making oxygen from the materials placed in bulk in a retort. In those cases, however, the tube being thin, was in stantly melted through; but in the present instance, the tube being very thick, and having an interlining of cloth, would resist for some time, and allow the white-hot flame of India rubber burning in oxygen to distill the interior rubber lining from the remainder of the tube, and drive it forward as inflam mable gas into the reservoir. While this was going on, the man in charge of the process was on his way, by a somewhat circuitous staircase and pas sages, to the cellar below, to see how the reservoir stood ; finding it less high than he expected, he probably lifted it, thinking it had stuck fast, and this rebel of pressure caused the flow of gas to be more rapid, and thus carry fire into the reservoir, now containing the explosive mixture. The gas nowhere passed through water on its route. The rubber tube was found to be completely stripped of its interior lining, and burnt quite through at one point near the retort, which remained undi turbed on the fire, from which it was removed by Dr. Jones, assistant medical director, a short time after the explosion. The ultimate cause of this accident we consider the absence of a wash-bottle in sight of the person managing the retort. With this adjunct, the grinding apparatus, in the hands of one posses sing the most moderate intelligence, is absolutely safe, but with out it, no process we have heard of is, with pure materials, more dangerous. With a wash-bottle in sight, a violent action resulting from an accumulation of material is impossible ; for if each charge admitted is not at once decomposed, we are noti fied of the fact. Thus all risk of igniting the rubber tube is avoided, or, if it should occur, the smoke would at once show in the wash-bottle. The rubber-tube might also be replaced by one of lead, but here a more serious danger is incurred in case of stoppage.—Journal of the Franklin Institute. Time of the Earth’s Rotation effected by the Accumulation of Meteoric Matter.—In a lecture delivered before the British Association at Dundee, Professor Alexander Herschell makes the fol lowing curious observation :—A question which at present agitates the minds of physical astronomers, is to ascertain whether a slight acceleration of the moon’s apparent motion can be attributed to an error in calculation, or whether the earth in the course of ages has lost in its speed of rotation. The lunar tables, which exactly repre sents the moon’s apparent motion at the present time, do not absolutely give the hour of an eclipse which happened when the sun was setting at Babylon, some hundred years B.C. The eclipse began, according to the table, when the sun was already below the horizon, and it would be invisible at Babylon. But if the earth’s rotation had been a little more rapid in former times than at present, the sun, instead of having set, would have appeared eclipsed before his setting, as was indeed the fact. To account for this change in motion, the friction of the tides has been considered, a slow accumulation of meteorities upon the earth’s surface would undoubtedly diminish its speed of rotation. The change of a hundredth part of a second in the length of the day, since the earliest observations, would explain the existing discrepancy. Fine Art Exhibition at Amsterdam.—An exhibition of the works of living artists, Dutch and. Foreign, is announced to open on the 7th September, in the present year, at Amsterdam, and to close on the 5th October, unless the directors see reason for the extension of the time. The exhibition is under the joint management of the autho rities of the town of Amsterdam and the Council of the Academy of the Beaux Arts. The programme includes painting, sculpture, archi tecture, engraving and drawings, but no copies will be admitted, whether in oil or otherwise. The Commission retains the power of admission or rejection, but liberally offers to pay the cost of transport of works sent by the ordinary means, but not by express. The time of reception is between the 10th and 24th of August, and the works are to be accompanied ’by a letter to the Commission de 1’Exposition Local de 1’Academie des Beaux Arts, Oudemanhuispoort, B 106, con taining the names in full, and the address of the artist, and (if for sale) the price of the work. The municipal authorities give six gold medals, of the value of one hundred florins each, but exhibitors may compete or not, as they please. Ths Camphor Storm Glass.—Professor C. Tomlinson King’s Col lege, W.C., in a late letter to the editor of the Chemical News, alluded to a paper published by himself in the Philosophical Magazine for August, 1863, in which he proved, that the instrument above named owed its crystalline changes not to variations in moisture, barometric pressure, light, or electricity, but simply to those of heat, and adds certain new points, among which is this. By dipping a piece of filter paper in ether, and placing it on one of those glasses, a crystalline de posit may be determined to any part at pleasure, in a few seconds, and will conform to any pattern or device we may give the paper. Great Organ for Notre Dame.— The French Government has ordered a very powerful organ of Messrs. Caville-Coll for the cathedral of Notre Dame, the restorations of which are just completed, and a special commission has been appointed to watch over and receive the work. The commission includes the composers Auber, Thomas, and Rossini, M. Benoist, professor of the organ at the Conservatoire, Baron Seguier, of the Academy of Sciences, several dignitaries of the Church, the Director of the School of Religious Music, M. Voillet-le-Duc, the architect, and several officials. Machine Packing.—In selecting the best material for packing, it will be found very useful to bear in mind the following fact:—If the material used is itself impervious, only so much pressure need be applied as will cause it to fit tightly against the adjacent parts; but if the packing itself is porous, then a far greater pressure will be de manded, to bring its particles into close contact, and so render it impervious. This fact, we think, has much to do with the acknow ledged superiority of rubber packing in certain cases.