vessels, and two dollars and fifty cents per ton for those of a smaller class.

The counsel for the defendants admitted that they had applied "Ericsson's propellers" to six vessels, each of 150 tons, and to one vessel of 340 tons.

The counsel for the defendants then called Dr. Dionysius Lardner, who testified that, before the date of the plaintiff's patent, he had seen propellers in England which had been patented by Mr. Perkins, and also by Mr. Smith. Models of them were produced, but the witness admitted that they differed substantially from the plaintiff's. He testified that the specification was vague and indefinite, and that he could not, from its directions, construct a wheel such as the plaintiff claims to have patented.

The deposition of Charles M. Keller was then read. He testified that he was a clerk in the Patent-office; that he had officially examined the two patents of Emerson and Ericsson; that, in his opinion, they were different, and did not conflict; and that he had made a report to that effect to the Secretary of the Treasury.

James J. Mapes, and William A. Cox testified that they were consulting engineers, and that they had read the plaintiff's specification; that it was vague and indifinite, and that they could not, from its directions, construct the wheel claimed by the plaintiff. Upon cross-examination, these witnesses stated that they were not practical mechanics.

Joseph Belknap, a draughtsman in the employ of Dunham and Co.; James Cochran, second engineer of the steamer Princeton; and George Birkbeck, jun., a person, in the employ of the defendants, stated that they could not, from the specification alone, have constructed the wheel; but that, with the aid of the corrected drawing made by Dr. Jones, they could have done so.

The Court charged the jury, that the patentee is bound to file a specification of his discovery, which shall apprise the public of his invention without ambiguity or uncertainty; that if they shall find that the plaintiff originally filed drawings, so that all persons might have examined them, and that such drawings were similar to those produced in the trial, then they might come in aid of the specification. He directed the jury to view it as the whole specification, and gather from it what the plaintiff intended to claim. His Honour then examined the terms of the specification in detail, and reviewed the testimony of the witnesses. He instructed the jury, that they must construe

the language as addressed to men skilled in this branch of art-and if a competent mechanic could, from it, have constructed the wheel, it is sufficient. If such a mechanic could not, from the specification, have constructed the machine, then the plaintiff must fail, unless he can help it out by the drawings; but these must be shown to have been filed with his original application; that in this case, the Patent-office and its contents having been destroyed by fire, he is compelled to supply the evidence the best way he can. The Judge then reviewed the evidence as to the drawing filed in 1844. He further instructed the jury that it had been contended that Emerson had abandoned his patent to the public by non-use; that this might arise either from positive abandonment, or might be implied from circumstances and if the jury should find that he had relinquished his right, then he could not maintain this action; that a patentee cannot lie by an unreasonable time, and allow his invention to go into use. The Judge then reviewed the evidence upon this point.

He further charged, that it did not appear to be denied, that if the plaintiff's patent was valid, that the defendants had infringed it; that the jury were bound, if they found in favour of the plaintiff, to give him a verdict for his actual damages; that in some cases the Court had instructed the jury, that they might, in addition, give damages to compensate the plaintiff for the expenses of the litigation-but that, in the present instance, he thought they ought not to find beyond the actual damages proved. He repeated, that the great question in the cause was, had the plaintiff established his right to the wheel commonly known as "Ericsson's propeller?"

The jury found a verdict for the plaintiff for 3,575 dollars and 6 cents, costs. It is stated that, of the jury, eight were practical mechanics.

The American Screw Steamer "Marmora," mentioned in our last, for the safety of which strong apprehensions were beginning to be entertained, arrived in the Mersey, from New York, on the morning of Friday, the 26th, after a passage of twenty-three days and a half. The length of the voyage is said to have arisen from injury to the propeller; it was made of wrought copper; and being struck by a heavy sea shortly after leaving New York, it was so much damaged as to be rendered not only useless, but seriously obstructive; it was bent out of its position, and had to be dragged after the vessel throughout the greater part of the voyage. The Marmora is handsome in its build. It is to go to Constantinople, and to be placed at the disposal of the Turkish Government.

the piston, e e, and which piston is firmly bolted to the flanch of the outside casing B at S; this outside casing is of iron, and its interior is occupied with atmospheric air, as shown at ff; the piston e is perforated, as shown at fig. 3, a; the apertures may be increased in size, as also in number. The action of the apparatus is as follows: K, the point of contact is struck and forces the cylinder, A A, up into the chamber, ff, and outside casing, B B, until the piston bottom, e, is in contact with D; this upward, or onward movement is retarded by the hydraulic action of the fluid in C C, the whole contents of which are forced through the apertures in the piston, e; the advance of the cylinder, A A, is also opposed by the action of the atmosphere on the upper or inner end of that cylinder. The united resistance of air and water is thus directly obtained. It will be readily perceived, that the size and number of the apertures in the piston, e, regulate the resistance of the water, which may be adapted to the vehicle for which it is intended to be used.

Fig. 2 represents a side elevation of two buffers applied to an independent carriage designed to follow the tender, and to be used as a luggage van or truck.

Fig. 3 is a cross section of a buffer on its guide-roller R.

Fig. 4, represents a buffer for a station terminus, or at the foot of inclined planes. A A, may in this instance be prolonged so as to shut up 10 or 20 feet if required; this would be a sure preventive to accident in those cases.

Figs. 5, 6 and 7, represent an application of the buffer to the locomotive

engine-front, side elevation section, and front view; the chamber, W W, is partially filled with water, the resisting power is double-acting-water and air supposed to afford resistance to the superior momentum of the locomotive engine. The length of space through which the resisting power of the apparatus is designed to act in the application of the buffer to carriages, is 3 feet 6 in. at each end, 7 feet in all. A train composed of twenty carriages would thus have a contractile power of 140 feet, a space sufficiently long by the application of a moderate elastic force to neutralize and render harmless the velocity of a fast train heavily laden.

The apparatus is capable of application in various shapes and forms; those indicated in the figures are of a heavy description; a much lighter apparatus is applicable to light carriages constructed for fast travelling.

HENRY RAYNER.

Ripley by Alfreton, Oct. 4, 1845.

ACCIDENTS IN COAL MINES, WITH A PROPOSITION FOR THEIR PREVENTION.

The recent mortality from coal-pit explosions is truly awful and startling; scarcely a month has elapsed since thirty lives were sacrificed at Crombach, in Wales, and more recently above fifty at Jarrow, and five at Aberdare. A year ago, this month, ninety-five were deprived of life at the Haswell colliery, and it is affirmed, by competent authorities, that in this kingdom alone no fewer than two thousand five hundred are lost annually!!

These facts call aloud for legislative interference, and appeal to science with a power far beyond that of eloquence. Previously to giving my own, it may be necessary to point out a few of the plans that have been suggested for ridding pits of noxious gases. Before the introduction of Davy's lamp it was proposed to ventilate mines by air pipes passing through all parts of the works to a common tube at the pit's mouth that should be made to feed a fire; the draught occasioned by the fire would serve to clear the mine of all noxious vapour. This mode was again suggested by a writer in Chambers' Journal for 1840. Another practice was for one of the colliers to crawl, serpent like, on his body, and with

a match to fire the gases and allow them to explode over him. This latter practice was very dangerous, and the former seems hardly feasible. Illuminating pits with the Bude-light was proposed by its inventor, Mr. G. Gurney. A correspondent in your Magazine for October, 1844, proposed to effect this by having a Bude-light at the bottom of the shaft, and by means of mirrors and lenses, made moveable by being fixed on ball and socket joints, to reflect the light to all parts of the pit; all this is undoubtedly impracticable. A great deal of fault has been placed to Davy's Lamp, which ought to have been laid to the charge of those who had its management. That instrument, as improved by Messrs. Upton and Co., is sure and philosophical, and though it cannot remove the mephitic vapours of a coal pit, it safely and distinctly indicates their nature and presence, and thus makes way for more powerful agents by which they may be expelled. The Literary Gazette for July last, contains an abstract of a paper read before the British Association by Professor Ansted "On the Ventilation of Mines." This gentleman proposes, with improvements, what has before been partially practised in some districts, viz. :—the sinking of extra shafts, as vents or chimneys, to the working shafts, and by placing at the bottom of these, furnaces, or grates, or pans of fire, so as to cause a free circulation of air in the paths or galleries of the mines. It will be much to tempt coal owners to sink extra shafts, bearing in mind the following fact stated by the Professor. "The coal trade is now hardly remunerative. It is a struggle in which every one endeavours to bring into the market saleable coal at a low price, and a struggle, obliging those concerned to compete with the utmost energy."-He further adds, "But the interests at stake are not those of moneyed men. The lives of thousands, and the wellbeing of the population of large districts are also involved; and it is the duty of Government to watch over and protect these." Professor Ansted thinks that many miners are killed by the carbonic acid that remains after, and is the effect of the explosion-not being able to make their escape they breathe this noxious gas, which produces immediate death. Carbonic acid gas is rapidly absorbed by water, and could an explosion of fire-damp take place and the