288

Lunar Occultations.

Lunar Occultations visible in Philadelphia, computed by MRS. CHARLOTTE S. DOWNLS, from the Elements published with the Occultation list for the United States Almanac.

The Immersions and Emersions are for Philadelphia, mean astronomical time. Im. for Immersion, Em. for Emersion. These abbreviations in Italics refer to those Immersions and Emersions which take place on the Moon's dark limb. N. App. for Near Approach. The angles are for inverted image, or as seen in an astronomical telescope, and reckoned from the Moon's North point and from its Vertex around through East, South, West, to North and Vertex again. For direct vision add 180°.

JOURNAL

OF

THE FRANKLIN INSTITUTE

OF THE

State of Pennsylvania

AND

AMERICAN REPERTORY.

NOVEMBER, 1844.

CIVIL ENGINEERING.

Description of Portable Leveling Instruments. By DAVID STEVENSON, F.R.S. E., F.R.S.S. A., C. E., Edinburgh.*

In examining a tract of country, I have often experienced the want of some portable, and, at the same time, accurate instrument, for ascertaining, in a general manner, the relative levels of different points, previous to determining the line of a more detailed survey. spirit-level without any telescope, having a common sight and crosshair attached, is sometimes used for that purpose, being fixed on a staff stuck into the ground. The large instruments commonly used in leveling, are also often employed, but neither of these instruments answers the object I had in view; the first being much too rude for the required accuracy, and the second too heavy for easy transport. The level represented in the accompanying drawing, was designed to supply this want. It consists of an accurate spirit-level, a ten inch telescope, and a compass, so arranged as to admit of being very portable. The telescope unscrews at letter A, so as to form two compartments, and the whole is packed in a pocket case measuring 6 by 23 inches; and the tripod on which it stands does not exceed the bulk of a thick walking staff.

Referring to the drawing, B C is the level, D a circular level, E the compas, F screw for adjusting focus, G the eye piece, H screw acting

* Read before the Royal Scottish Society of Arts, 12th of February, 1844. VOL. VIII, 3RD SERIES. No. 5.-NOVEMBER, 1844.

25

on spring K L, which is fixed to the telescope at M, by a crutch on which it moves, N the screw by which it is fixed to the tripod, OPQR the top of the tripod, which contains a ball and socket joint, shown in dotted lines, which can be clamped and unclamped by means of a screw wrought on the inside of the part S T. In setting the instrument, the screw ST is first unclamped, and the instrument is moved by the hand on the ball and socket joint until the air bubble of the

level D, occupies the centre of the circular box containing it. The screw ST, is then clamped, and the instrument being directed to the object to be observed, the final and more perfect adjustment is made by bringing the air bubble B C, to occupy the centre of its tube, which is done by means of the screw H, which acts on the spring K L. The tripod is that used by Dolland for the camera lucida, and answers both instruments. The telescope can be made either, as in ordinary

levels, to reverse the objects, or, as in theodolites, to show them in their true positions. In this level, made for myself, I have adopted the latter construction, in order that the instrument may answer more perfectly the purposes of a field telescope. The addition of the compas is also a further convenience.

In connexion with this instrument, I have also had a portable leveling staff made, which also is shown in the engraving. It consists of an elliptically-moulded staff three feet three inches in length, and cut through the middle; the two halves are hinged at one extremity, and, when unfolded, are fixed by a spring at A, forming a rod six feet six inches long, on the flat side of which the graduations of feet and inches are painted; when closed, the graduation is protected from injury, and the whole forms a convenient walking staff.

These instruments, which were made for me by Messrs. Adie, of Edinburgh, I have found very convenient; and, I am persuaded, they will be suitable in all circumstances where the combination of accuracy and portability is required.

Edinburgh New Philos. Journ.

LIPSCOMBE'S Patent Apparatus for lessening the vibration and noise of Railway Wheels.

It is now generally understood that the rapid deterioration as regards the strength of railway wheels and axles, is chiefly caused by the intense vibration to which they are subjected. This can readily be made evident:-If the journal of an old railway axle is struck with a smith's hammer, it will, in many cases, break off with a single blow, presenting, at the fractured part, a weak, brittle appearance; whereas the journal of a new axle will take several hundred blows before breaking, a tough, fibrous appearance being presented at the fractured part. Suppose a finger to be in the act of creating a musical sound by laterally distending a harp string, it is plain, if the finger is taken away, the elasticity of the string will cause it to fly to and fro, until, from the friction of its fibres, the string is brought to a quiescent state. Now it is clear that the same effect would be produced by deflecting the harp string with a weight, and suddenly withdrawing that weight. We thus see, as the weight upon a wheel in motion is ever shifting, the particles composing a wheel are successively deflected every revolution, the weight shifting with a rapidity depending upon the speed of the wheel. It follows, as in the case of the harp string, that the deflected particles, immediately the weight is shifted, will begin and continue to vibrate until the wheel stops; the consequence is either the spokes become loose, thus rendering the wheel useless, or the particles of the wheel by being wedged and dove-tailed together, become, by this wriggling motion, so loosened and broken, as, in a few years, to render the wheel unsafe, consequently useless, from its great decrease of strength, although the actual quantity of metal in the wheel remains the same as ever.

The same remarks are applicable to railway axles.

The vibration which takes place in a wheel is communicated to the axle, as the axle is struck by the vibratory particles of the wheel. That this is exceedingly destructive to wheels and axles, is sufficiently attested by their great decrease of strength, and the pecuniary loss every railway company sustains from this cause, together with the accidents which have occurred by the breakage of axles.

Mr. Lipscombe, after a variety of experiments, ascertained that any metallic body could be prevented from vibrating, by simply pressing a quantity of sawdust, &c., in contact with it, so that when the particles of a body are deflected by a weight, their elasticity, when the weight is withdrawn, is spent in forcing back the sawdust, while resuming their original position.

An apparatus was constructed and applied to the wheels of a ballast wagon by way of experiment, and exceeded the most sanguine expectations formed of it. It completely prevented vibration, not only in the wheels, but in the axles; the noise of the wheels was very slight, the little noise produced being occasioned by passing over loose, or sunken, joints, and the wheels, as may be supposed, from the absence of vibration, had a very easy motion.

The patentee subsequently, through the recommendation of Mr. R. Stephenson, obtained permission of the directors of the London and Birmingham Railway, to apply his apparatus to one of their first class carriages. Previous to the wheels being placed under the carriage, one pair, with the apparatus applied, was slung off the ground, and struck in various parts of the axle and wheels, but not the slightest vibration could be detected. Another pair not fitted with the apparatus was afterwards slung in a similar manner, and when struck, produced a sound as loud and prolonged as a bell would have done. The carriage has been running daily with the trains for upwards of nine weeks, and is a great favorite for its peculiarly smooth motion, and comparative noiselessness, although, from being in a train with carriages before and behind it, the ears are assailed by their noise. The apparatus is very simple, consisting of a plate of zinc placed on each side of a wheel, for the purpose of retaining sawdust, in contact with part of the rim and spokes; each plate has two wooden rings of unequal size, permanently fixed to it, the external diameter of the smaller ring, and the internal diameter of the larger ring, are shown by dotted circles in the annexcd figure, and are likewise flush with the edges of the zinc plates. The combined depth of the corresponding rings is equal in

width to the tyre; these rings meet and are screwed together, certain parts of the rings being cut away to let in the spokes. By a reference to the figure, it will be seen that the ends of the spokes, adjoining the