at the same time, a space on the paper for the next letter is produced. The blank between each letter, or word, may be increased by raising the hammer twice, or thrice, instead of once. The successive letters are brought up to the hammer, by the means before alluded to. There is also a prepared paper (black,), which may be put over the white paper at discretion, the object of which is to enable persons who have their sight to read the printing better, the force of the hammer causing the black paper to 'set off." At the hammer end of the case a piece of cloth is attached, to place between the hammer and the type, so that the letter may not be bruised. The type in the slide was made of wood, but to metallic letters the instrument would be equally applicable.-Proc. Brit. Assoc.

Lond. Athenæum.

Meteorological Observations.

The President remarked, that meteorological observations required the atmosphere to be in a very peculiar state, in order to insure accurate definition. He believed it was Struve who first remarked, that whenever the temperature of the night sunk much below the mean of the preceding twenty-four hours, no accurate definition of objects was to be expected. Dr. Robinson said the hygrometrical state of the air was of much consequence for astronomical observations; he found that it required to be very near the point of saturation, as a difference between the wet and dry bulb thermometers of more than a degree, or two, precluded all accurate definition, the brighter stars having then a tendency to throw out scintillating lines; and it was only in the moist state of the air that they appeared distinct in themselves, although surrounded by faint colored rays.-Rev. Dr. Scoresby remarked how one branch of physical research bore upon other branches. He believed that the hour at which Lord Rosse found that he could best test the accuracy of figure given to his splendid reflectors, was that which Sir David Brewster had ascertained to be the time of mean temperature for the twenty-four hours.-Lord Rosse said, that the test being the formation of a distinct image of a watch dial placed at a considerable elevation, say 100 feet, above the tower, it was neces sary, in order that there should be no tremor of the air, that the temperature within and outside the tower should be as nearly equal as possible, and that this was pretty much the time of the mean temperature of the day-about twenty minutes past nine in the morning.(Ibid.)

Ibid.

JOURNAL

OF

THE FRANKLIN INSTITUTE

OF THE

State of Pennsylvania

AND

AMERICAN REPERTORY.

MARCH, 1845.

CIVIL ENGINEERING.

On Wooden Railways. By Mr. W. BRIDGES.

The lecturer commenced by adverting to the fact, that lines of railway were now extended southward to Brighton and Southampton, westward to Exeter, north-west to Birmingham and Liverpool, east and north-east to Norwich and Ipswich-while the city of York, the port of Hull, and all the towns on the direct north route, were left to find a circuitous approach to the metropolis. He, however, contended that although occasion of surprise, this was hardly matter for regret, inasmuch as new science, and new systems might now guarantee the construction of a railway from York to London, at a fourth, or fifth, of the cost ten, or twelve, years ago. Amongst these new systems, the most valuable was the proposed recurrence by Mr. W. Prosser, with certain striking modifications, to the ancient wooden railway. These modifications were-1. The chemical transmutation of the fibre of the wood into a more durable, hard, and almost incorruptible, substance. 2. The employment of a beveled guide wheel, fixed at an oblique angle before and behind each carriage, as a substitute for the flanch, which is the main cause of the wear and tear on the existing railways. By means of this guide wheel, the bearing and carriage wheels would be quite flat, obviating all abrasion of the wood, as well as all liability to oscillation. Under such circumstances, each wheel is permitted to act independently, as with the wheels of an ordinary carriage, and the carriage would be placed upon the ordinary carriage springs. Mr. Adams, the great coach builder, was strongly impressed with the value of the proposed modification, and anticipated, from the use of such carriages, that railway traveling might be VOL. IX, 3RD SERIES-No. 3.-MARCH, 1845.

13

henceforth perfectly smooth and noiseless. The process by which the wood is chemically transmuted is the injection of two salts, alkaline and metallic, (known by the name of Paynizing,) which salts, by decomposition, produce an insoluble matter of the timber, arresting and destroying the vegetable principle-so to speak, fossilizing the wood. It was to be noted, that the wood tram was not a noveltythat Mr. Prosser's invention was undeniably a recurrence to the "wisdom of our ancestors," but under such peculiar modifications as made such recurrence eminently desirable, as a means of obviating the incalculable inconveniences and expense of the present mode of railway construction. The first step in this, the right, direction was, the adoption of longitudinal sleepers on the Great Western Railway, and that experiment had been eminently successful-the Great Western, with all its wear and tear, and other evils common to all iron railways, being the best railway yet constructed in Europe. The rails, then, or rather trams, are indurated by the process of Paynization, and are laid down on the principle of the old tram roads, let into wooden sleepers, and secured therein by wedges, forming one great frame of longitudinal and cross sleepers on the leveled surface of the ground. The tires of the wheels being perfectly flat, are kept in the even tenor of their way by two guide wheels before and behind each carriage, fixed at an angle of 45° to the horizontal line; two tires, in their circumference at right angles to one another, embrace the upper and inner edge of the tram. All the wheels being on separate axles, the inner and outer wheels adapt themselves with safety and facility to the sharpest curves. The great advantage of wood over iron, presuming its durability to be secured, is, the adherence of its surface involving about double the tractive power of iron. Much fallacy existed on this subject, and this very adhesion was often alleged as a reason against the adoption of the proposed system; the objection was based on a confusion of friction and adhesion. The driving wheels of the engine are pressed to the rail by a certain. weight-say that of the engine itself-and this pressure produces between the wheel and the rail a certain amount of adhesion; upon iron railways this weight is necessarily increased in an inordinate degree, to counterbalance the want of adhesiveness of surface. If the engine were prevented from moving forwards by some immovable obstacle, and were also powerful enough to overcome this adhesion, the wheels of the engine would revolve, although the carriage made no progress; if the obstacle were diminished, so that it will give way before the adhesion is overcome, the engine advances. The magnitude of this obstacle, which is thus capable of being removed, is to be measured by the amount of adhesion-for, if its resistance be greater than that adhesion, the obstacle will not be removed. The total amount of resistance to progress on a railway is correctly represented by such an obstacle; and there is an amount of train which an engine of a given weight will not draw, whatever its power, for its wheels will rather revolve than draw the train. This adhesion, and, therefore, the source of tractive power, is double with an iron wheel on a wood surface, than on a surface of iron. In ascending a gradient, the engine has not only to draw, but to lift; if the adhesion, or bite, be

small, the engine must be preposterously large, to draw the train on the level portions of the line; increase this bite, or adhesion, and you may increase the steepness of the gradients, and diminish the weight of your carriage. This immense saving may be made in cuttings and embankments, as well as in the carrying establishment, and in the locomotive power. The truth is, that since the era when it was universally received that the periphery of a wheel could never act as a propulsive fulcrum, engineering science has only been gradually awaking to the immense importance of this one principle of adhesion; and the establishment of sound views here must lead to the universal adoption of wooden railways. A striking proof of the durability of Paynized wood was afforded in the fact, that a tram had been laid down at Messrs. Dalton's wharf, at Vauxhall, on the 15th of August, 1843, and the quantity of coals and other goods that had passed over it up to the 1st of May last, was 37,000 tons, without producing any perceptible effect upon its surface. Prepared beech had recovered the deflection of three-eighths of an inch, resulting from a pressure of 140 tons on the tire of a wheel; and on an experimental tramway the carriages had passed over a number of times, (28,000) equal to a year's traffic on an ordinary railway without obliterating the saw marks. Mr. Bridges submitted various calculations, to exhibit the probable economy of the process, the result of which is, with respect to superstructure, that a double line might be laid down for about 17007. per mile, instead of from 3500l. to 4000l., the actual cost of iron rails. Mr. Vignoles had assumed, that by taking gradients of 1 in 230, instead of 1 in 330, on the Irish south lines, the cost of railways in that country might be reduced from his first estimate of 13,000l. to 11,000l. per mile. A still wider range of choice, both as to gradients and curves, would be afforded by the adhesive principle of a wooden line, now advocated; and the probable total cost of an Irish line, including earth works, masonry, fencing, land, upper works, carrying establishment, parliamentary expenses, and contingencies, would not exceed 6000/-and, by making use of Scotch fir, instead of beech, (and the greater porosity of the former timber renders it more susceptible of the chemical action,) probably not 5000l. per mile. As an important aid to the construction of wooden railways across the soft and boggy districts of Ireland, Mr. Bridges shortly adverted to the very simple and philosophical pile sinking apparatus of Dr. Potts, which substitutes pneumatic power for manual labor and the 'monkey.' Dr. Potts employs hollow tubes of iron, or Paynized wood; the lower extremity is open, and to the upper extremity is affixed an air-tight cap, with a flexible tube of jointed metal, or elastic hose, extending to a receiver, from which the air is extracted by suction; when the air within the tube is thus exhausted, the mud and shingle flow into the tube, which then rapidly descends by its own weight, and the pressure of the external atmosphere. Finally, the importance of the introduction of economical railways into Ireland at this moment were held to be of more consequence than any which legislation, either of Parliament, or a Federal Convocation, or a Repeal Congress, can possibly effect-by giving employment to the population of that country,

by developing her vast yet hidden resources, by opening markets for her produce, by uniting her more closely with other countries, and by increasing the happiness and comfort of her inhabitants. An animated discussion ensued.

Mr. Fairbairn observed, that one hundred and fifty years ago wooden railways had been very general over a great part of the north of England, but that the expense of repairs had set invention to work to discover new modes, and this search had resulted in the present system of iron superstructure. There could be no doubt, however, that by such a system as the present the prime cause of the destructibility of the wooden trams might be removed, and, in that case, wooden railways might be re-established with advantages. The invention exhibited by Mr. Bridges, seemed very good and ingenious.

Dr. Scoresby, in commenting on the subject, gave a very interesting account of the working of wooden railways in America, which, from the simple and unoruamental character of the works of art, and other causes, were certainly very economical. The desideratum was such a guide wheel as that of Mr. Prosser, which he hoped would now attract attention and investigation.

Dr. Greene characterized the invention as exceedingly beautiful and simple, and illustrated the safety principle of the guide wheel by a diagram, showing that the centre of motion had actually to describe an arc of 45° before the train could be in even the same liability to yield to the centrifugal influence as the present railway train in its natural position. Indeed, he considered the action of this oblique wheel to be totally different in character and rationale from the ordinary flanch.

Inquiries were put to the lecturer as to the different susceptibility of different kinds of timber to become indurated by Paynization.Mr. Bridges stated that the harder woods, such as oak and lignum vitæ, would hardly be benefited by the process, which acted with most effect upon the more porous woods; indeed, he held it to be a sufficient advantage to make Scotch fir equal to oak, without professing to transmute oak, or lignum vitæ, into iron.

The President briefly explained the chemical action of the two solutions injected into the wood, resulting in the formation of gypsum, or plaster of paris, within its pores.

Dr. Scoresby gave a detail of experiments he had made to test the effect of salt water under high pressure upon different kinds of timber. He had placed pieces of fir, cork, oak, &c., at such a depth in the sea as to sustain a pressure of eight tons to the inch, and the result was, that every piece of wood became of exactly the same density.

Prof. Byrne suggested that the fibres of the wood should, by means of blocks, be placed vertically, instead of horizontally, to insure greater durability.

Mr. Roberts, admitting that he had not come in until after the lecture was delivered, expressed scepticism as to the value of wood as a superstructure; but the chairman notified to him that certain chemical and mechanical means were employed to harden the wood, and to protect it from abrasion.