image at the eye end measured with the declination micrometer. The telescope was next turned over till it rested in a horizontal position pointing south, and the place of the image again measured. In two readings, taken in 1850, the difference was Or. 204, 0.00414in., one-half of which, or 0-00207 of which, was the effect of flexure, a variation of no practical importance. The flexure is now regularly noted from time to time, by a process hereafter described. The meridian of Greenwich, as stated in school books, is an imaginary line, passing through Greenwich from the north to the south pole; and by noting the instant that fixed stars cross this line, Greenwich time is obtained. Unfortunately, the line is imaginary; hence the difficulty of ascertaining exactly when the stars cross it, so one by one the astronomer has to eliminate the sources of error. He, however, can easily find the zenith, also the centre of the small orbit described by the North Star; so, should he first point his telescope to the zenith, and then depress it till he sees the North Star, the telescope will have described a segment of circle in the true meridian of Greenwich. On looking through the telescope a number of fine vertical wires are seen crossing its field of view, the central one in the axis of the telescope representing the meridian; so, were the whole of the apparatus perfect, every time a star passes that particular wire it would also cross the meridian. Although the transit tube, with its iron axis and stone supports, only has the power of swinging over from the north to south, and cannot be turned toward the east or west, the mere mechanical arrangement is not sufficiently accurate for astronomical purposes. For instance, should the tubes yield a little, the micrometer wires shift, or other faults in telescope itself appear: a distant object in a line with the longitudinal axis to the telescope will not be represented by the object glass exactly upon the central micrometer wire, but to the right or left of it; so, should the astronomer register the time it is seen to cross that wire, he will do it at a period when the star is not on the true meridian. This source of inaccuracy in time and calculations is known as "the error of collimation." Now, if one fine perpendicular wire were fixed ten miles to the south of the transit tube, and another ten miles to the north, both being exactly in the meridian, the astronomer could first point his transit tube to the south wire, and make its image fall upon the central micrometer wire by adjusting the latter, and then, on turning the tube over, if he found the north wire also coincide with the micrometer wire, he would know that he had the true optical axis of his telescope marked by the wire representing the meridian. Two fine wires, however, cannot be fixed in those positions a few miles on each side of the Observatory, or if so fixed could not be seen when wanted. If they were fixed in the walls of the room they could not be brought to a focus in the great transit telescope, so the alternative is to fix them on each side of the room, interposing lenses between the wires and the telescope to atone for want of distance. of micrometer screws. To view one collimator by the transit circle telescope is easy, but to view one collimator by the other the transit circle has to be raised out of the way by mechanical appliances, and this is done every Monday. An observation for the collimation of the transit telescope is made every night, the axes of the telescopes used as collimators, having previously been brought into the same line with each other, or at all events strictly parallel. The central vertical wire of the telescope is then brought several times in succession upon the proper point of the nearly vertical wire of the north collimator, and the same operation is performed with the south collimator, the micrometer being read for each coincidence. The mean readings of both give the reading for the position of the Kine of collimation. The interior of the tube, its glasses and wires, being now all right, or the amount of error known, the outside requires attention, for should the pivots on which it turns be out of level, the telescope will be tilted on one side, and not point to the meridian; consequently, the unfortunate astronomer will see the star cross the micrometer wire before or after it is on the meridian, and he will register the real time of transit incorrectly. Thus it is necessary to test even the polished iron axis and its bearings, and this "error of level" is ascertained, not by a spirit level, but by the following very ingenious and simple contrivance. The transit circle telescope is turned completely upside down, till it points to a trough of mercury beneath. A ray of light from a gas jet is then thrown from a glass plate E on all the micrometer wires, which are thus brilliantly illuminated. Should the horizontal axis of the telescope be perfectly level, the observer will see only one set of wires, because the reflected images from the mercury will be thrown back upon, and exactly coincide with, the real wires. Should the pivot be out of level, the real and reflected wires will not coincide; consequently, the observer at E will see two sets of wires, one set rather more brilliant than the other. In the cut, the central micrometer wire C illustrates the principle. Should the pivot not be out of level, one wire only will be seen at C. Should it be out of level, for instance, at B, the dotted lines show how the image will be reflected by the mercury to D, whereby the astronomer will see two wires, B, D, instead of one. By moving the micrometer wire the two sets of wires are made to coincide, the mean of the micrometer readings is taken, and the difference between the mean reading and the reading corresponding to the line of collimation, is the error of level. The principle being thus explained, we cannot do better than quote the technical description of this arrangement in the words of the Astronomer Royal:-"For determining the error of collimation two horizontal telescopes of about 5ft. focal length, and nearly 4in. apertures, with their object glasses turned towards the centre of the instrument, are But the cares of the astronomer are not yet over, mounted on Y's, which are carried by massive If the Connecticut witches, who, as everybody brick piers, one on the north and one on the south knows, once swept the cobwebs out of the sky, had side of the transit circle. The height of the only left one thread in the true meridian of Greenaxes of these telescopes is as nearly as pos- wich they would have saved a deal of trouble. The sible the same as that of the axis of the true central line of the telescope has now been transit circle. Each telescopo is furnished ascertained, as well as the level of the pivots; conwith wires in its principal focus, to be used sequently, the tube will do to take an observation as collimating marks; and each telescope may be of a star crossing the zenith. Should, however, one used as a collimator for the other, or for the transit of the pivots be too far north or south, on turning circle telescope. The system of wires is the same the telescope over towards the horizon, every inch in both, consisting of two parallel wires inclined of that motion will make it point more and more to the vertical at an angle of about two and three-away from the meridian. This is known as the quarter degrees, two other parallel wires at right "azimuthal error," and is not very difficult to angles to the former, and therefore inclined to the ascertain. Should the tube first point to the zenith horizontal line at the same angle (the intersection and the axis rest truly east and west, on the turning of this pair with the former producing a square), the telescope over it must at last come plump upon and a fifth wire parallel to the two last mentioned, the North Star, the whole of its motion being in and at a distance from the nearest of about ten times the side of the square. The middle portion of the fifth wire, which is included by the two nearly vertical wires, is in the same vertical with the middle of one of the nearly vertical sides of the square; and these middle points are the points adopted for observation. These wires are finer than the others." The frame carrying the north collimator wires are adjusted in altitude, and the frame of the south collimator in azimuth, by means the true meridian. As a matter of fact, the mechanical portions of the apparatus are so well made, that on swinging the telescope over the North Star does always come into view, but the North Star has an apparent orbit, the centre of which is the true north, and not the star itself. The azimuthal error, then, is determined by observations of Polaris, or of & Ursa Minoris, at consecutive passages above and below the North Pole. Other stars also can be employed sometimes; for instance, meridian of Greenwich, and C the zenith. Should the eastern pivot of the transit circle telescope be too far north, a line A B through its centre, instead of coinciding with the true meridian, will cut the circle at A and H. As Polaris takes twenty-four hours to complete the circle, if the telescope pointed to the true north, the star would cross its field at K, and exactly twelve hours afterwards at E. If, however, as in the cut, it did not point to the north, the star would cross it at H, apparently behind time, and again at A, apparently before time, the whole interval being considerably less than twelve hours. This period of time gives the data from which the azimuthal error is computed. The azimuthal error tables commonly used at Greenwich are for the most part based upon observation of Polaris above and below the pole. The angle of error is computed from the zenith, at C. The cast iron graduated vertical circle of the transit instrument, for "zenith distance" observations, is 6ft. in diameter, with two sets of divisions. The set on the western side is cut upon a band of silver let into the iron, and divided into five minute spaces, which have to be read by microscopes; the other side is divided by points to every five seconds. There are six reading microscopes, which are simple perforations through the stone pier, having their object glasses inside, next to the graduated circle, and their eye-pieces outside, in a circle about 21in. in diameter. Such are the leading features of the great transit circle at Greenwich Observatory. After all the care that is necessarily taken to learn the amount of the sources of error, it does not follow that when an observation is made that the telescope itself points to the true meridianal line. Its deviations from that line are, however, known by the above tests, and the error allowed for by calculation rather than by adjustment of the instrument. The error of collimation is much under control, and kept very small by adjustment, the remainder being allowed for in the calculations. The altazimuth instrument, as represented in our engraving at fig. 1, was erected in 1847, specially for lunar observations, Mr. Simms being the optician, and Messrs. Ransomes and May, the engineers. Like the great transit circle, it has a very firm foundation, consisting of a three-rayed pier of brickwork, built up from the solid ground, and having no connection with the building. The radial arms of the iron triangle, supporting the upper part of the instrument, rest upon a smaller pier on the centre of the brick pillar. All parts of the frame possess great firmness, the principle of construction adopted being to make as much of the instrument as possible in single solid casts of metal, to avoid the use of small screws, and to give the observer no power of adjustment. All errors are calculated by the methods already described, and 'allowed for when reducing the observations. The altazimuth instrument, like the great transit circle, has a room to itself, with the usual mechanical appliances for opening and closing the shutters in the sides and roof. The Astronomer Royal thus describes the instrument:"For the support of the upper pivot a horizontal iron triangle is carried by the threerayed pier; on each side of this there is mounted a vertical iron triangle; and the three vertices of these are connected by an upper horizontal iron triangle: three radial iron bars, supported on its angles, carry, at their point of union, the Y in which the upper pivot of the vertical axis turns. The frame revolving in azimuth consists of a top and bottom, connected by two vertical cheeks, all of cast iron; the microscopes for viewing the divisions of the horizontal circle are cast in the same flow of metal with the bottom piece, and those for viewing the divisions of the vertical circle are cast in the same flow with one of the vertical cheeks. The vertical circle and telescope are of gun metal; the side of the circle which carries the graduated limb, the ends of the telescope, and one of the pivots, being cast in one flow; and the other side of the circle and its pivot cast in another flow. The diameters of both circles (horizontal and vertical) are 3ft.; the length of the telescope is 5ft.; the aperture of its object glass 33in. The top carries two levels and the bottom carries two levels, parallel to the axis of the vertical circle; the vertical cheek which carries the microscopes carries also two levels parallel to the plane of the vertical circle." The reflex zenith tube, made on a peculiar principle, was designed by the Astronomer Royal, and constructed under his directions, by Mr. Simms in the year 1851. The following is the principle of the instrument:-The star to be observed (v Draconis) is so near to the zenith, that it may be seen with ease by an object glass whose axis is immovably fixed in a vertical position. When the star passes overhead, an image of it will be formed at the distance from the lens equalling its focal length. If, however, a trough of quicksilver be placed below the lens, at half the focal distance. the image of the star will be formed upon the object glass itself. Should the mercury be placed at a distance of more than half the focal length, the image will be formed below the object glass; if at less than the focal length, above it. Assuming the lens to be truly placed, and a star to pass over it exactly in the zenith, when the star crosses the vertical axis of the lens its image will be formed exactly at the centre of the object glass. Should the star not be exactly in the zenith, it will not pass over the true centre of the lens ; consequently, the image reflected from the mercury will be formed at the same distance on one side of the centre of the lens as it entered on the other, the point between the two spots being the true vertical axis of the lens, and the true zenith. The angle given is the basis on which the calculations of the zenith distance of the star are founded. To find the true vertical line with which to compare each observation a micrometer is attached to its movable cell, and the micrometer wire placed upon the image of the star; the object glass is then turned half way round, the micrometer wire is again placed upon the same image, and wherever the centre of the object glass may be, the vertical line which gives the means of computing the angular zenith distance is exactly in the middle of the space over which it was necessary to shift the micrometer wire. A little consideration will show that it does not matter whether the object glass revolves round its own centre, or any other vertical line passing through it. It is necessary that the azimuthal movement, or the movement of the lens round its vertical axis, be an accurate rotation round one vertical line; consequently, the object glass must be carefully mounted. served with this instrument, is not in the zenith' spiral line at regular intervals, the sidereal time of The last refracting telescope at Greenwich, the Some of the foregoing details will prove the excessive care taken to test the occuracy of the line of reference, the flexure of tubes, the true position of the pivots, and all the parts liable to error, the occurrence of each and all of which has a tendency to introduce inaccuracies in the calculations, and errors in time. These points being all known and provided for, it remains to register the true time of the passage of a star as it is seen through the telescope to cross the micrometer wires. One hand of the observer rests upon the end of the telescope near the eye-piece, and all he has to do is to tap with his finger a small button beneath his hand every time the star passes a micrometer wire. The true instant of time of each tap is recorded as follows, by means of galvanic chronographic apparatus. A large brass barrel, revolving in two minutes of sidereal time by means of clockwork, is covered with a layer of woollen cloth. A sheet of paper is wetted, wrapped round the, cloth, and its folding edges fixed by gum. This has to be ruled with one long line, in a fine spiral passing from end to end of the barrel, which to the eye appears to be Fig. 2 is a section of the object glass, and upper numerous parallel lines passing all round the part of the reflex zenith tube, the tube itself, and barrel, each of them only about one-tenth inch the cup of mercury below being omitted. S is the apart. A pricker is carried very slowly along the eye-end sliding in a socket. It comprises the third top of the barrel, and pricks a dot every second on and fourth lenses of the eye-piece, or the field-glass the long spiral line on the barrel. It only makes and eye-glass. R is the bent arm carrying the fifty-nine pricks to the minute, leaving a blank at eye-end of the eye-piece. Il is the flange of the the sixtieth, which serves as a mark to distinguish sliding tube. Its edge is graduated for azimuth, each minute. Here there is a barrel, covered with the readings proceeding to 360deg. I is the a long spiral line, and a pricker marking the time highest part of the sliding tube in which the rota- on that line with chronometrical accuracy. But ting apparatus is inserted. I is the sliding tube. there is a second pricker, which only makes a D is the fixed tube of the instrument. NN the mark when the observer of the passage of the star two bars carrying the diagonal reflector. O the taps the button by the side of the eye-piece of the diagonal reflector, a prism of glass. The inclined telescope, and these marks are pricked in the face and the lower or horizontal face are plane, white space between the two lines, so are at once but the vertical face is convex, and thus discharges distinguishable from the marks of the seconds the office of the second lens (counting from the ob- pricker, which always fall upon the lines. The ject glass towards the eye) in a four-glass eye- accompanying cut shows the manner in which the piece. The star y Draconis, which is to be ob- barrel is ruled and seconds dots marked on the The accompanying cut shows the arrangement of the prickers side by side, as they pass over the barrel, one of them being elevated and the other depressed. When the lines are to be ruled, a pen filled with ink and water is substituted for the seconds pricker. The electrical circuit is broken, and the barrel directly connected with the heavy clock weight, which makes it spin round with great velocity, and a fine spiral line is marked on the paper. A feeble battery is used to do the regular work, having just sufficient power to bring down both the prickers, when they chance to fall at the same instant of time. This refined piece of mechanism might naturally be supposed to complete the apparatus necessary to observe the passage of a star with accuracy, yet such is not the case. In using all delicate instruments the operator himself becomes a part of the mechanism. A locomotive may be perfect in all its parts, yet its speed depends upon the will of the driver. The telegraph companies are obliged to consider the clerks as an essential part of the instruments, a part also commercially affecting the interests of the shareholders, and the speed of transmission of messages through a given wire. It is the same at Greenwich, for unattainable perfection is required in the living part of the transit instrument. We may here call attention to the curious fact that no two observers looking through a transit telescopo see the same star pass the micrometer wires at exactly the same period of time. The French Astronomer Royal, in fact, has been recently making experiments to determine his own "personal error." It is just the same at Greenwich Observatory. The astronomers there rarely see the same star alike: one always sees it pass a fraction of a second before or after another, but this difference is nearly invariable. For instance, B. will always see it pass a little before A., and never a little after, except perhaps in cases of illness, or other extreme disturbing cause. The more curious fact is, that there is no possibility of determining who is right or who is wrong, but the constant quantity of the variation admits of a standard being chosen, and considered as the right one, which it is for all practical purpose. After a very long series of experiments, the Astronomer Royal determined to accept Mr. Dunkin as the standard observer at Greenwich, and the following table shows the variation from the standard, or Mr. Dunkin, as deduced from those experiments. In the table (-) means "before," and (+) means "after." Criswick D C Lynn D-L Carpenter D-JC Dolman D M D + 0.07 +0.11 0.00 -TC = 0.12 - N == 0.05 D 1 It will be noticed, however, that out of all these observers, two, Messrs. Dunkin and Roberts, chance to read the passage of a star alike. The figures applied for the correction of the observations of each reader are styled in England his "personal equation," and in France his " personal error." THE following is a return of the quantity of coal exported from the Port of Grimsby, September, 1868: -To Belgium, 970 tons; to Denmark, 1,535 tons; to Egypt, 1,896 tons; to France, 5,290 tons; to Hanseatic towns, 935 tons; to Holland, 575 tons; to Norway, 765 tons; to Prussia, 3,688 tons; to Russin, 1,568 tons; to Sweden, 1,298 tons; to Spain, 376 tons. Foreign, 18,896 tons; coastwise, 4,429 tons -total, 23,325 tons. Correspouding period, 1867Foreign, 24,323 tons; coastwise, 2,868 tons-total, 27,191 tons. Decrease, 1868, 3,866 tons. HYDRAULIC BRICK PRESS. spring Q which in its turn is supported by the box shoe magnets, so united as to form one compound To the north and south poles of this MEMOS. Buth," 'have recently patented some, in nut wheel S to the right or to the left by means of compound magnet, independent electro-magnets ESSRS. R., J., AND L. BODMER, of Newport, R bolted to the press bottom A. By turning the magnet. provements in hydraulic brick presses, which form wheel T, shaft T1, and hand wheel U, the spring are fixed vertically, their upper ends being inthe subject of the accompanying illustration. They is compressed or eased and the shaft F3 raised or serted through holes in a brass plate, and planed consist in arrangements for regulating the feed and lowered. The spring Q must either be of sufficient off so that the iron and brass present one smooth for ensuring a more uniform filling of the moulds, power to support the weight of shaft F 3 and parts and for adjusting the lift of the follower so as to belonging to it, or the weight of the same must be flat surface. The handle employed in sending mescause the mould bottom plates to rise exactly to the partly balanced by a lever and sliding weight keyed sages gives motion to a thick eircular plate of soft level of the mould table when the finished bricks on the shaft H 2. iron which is supported above the compouud magnet are raised from the mould. Fig. 1 represents a front Fig. 3 represents another mode of regulating the by a suitable socket-piece. The edge of this plate elevation of a press, in which the pressure is given feed. The shaft F 3 carrying the followers is made is divided into twenty-eight equal spaces, which in a downward direction, and fig. 2 is a vertical tubular or hollow at its lower end. As represented, are alternately notched cut right and left, so that section through line a b of fig. 1. The press bottom the shaft F 3 is raised to the top of its stroke, when there are fourteen projections or teeth, and fourA supports on two pillars A the press head B, lowered bush P 1, spring Q, and bolt P will enter teen corresponding spaces. The iron plate, in its to which is bolted the ram B 2 of the hydraulic into the tubular part of the shaft F 3 till the closed rotary movement, lightly rubs the brass plato pressure cylinder B 1. The feed slide box C, filled end of the tube comes in contact with the bush through which the ends of the electro-magnets are with material from the box Z, which latter is con-P. When the hydraulic cylinder with fallers drops stantly supplied from a shoot or hopper, is moved upon the material in the moulds the shaft F 3 will inserted, and as the projections and spaces at the forward by a feed slide cam E through levers E 1 and depress bush P1 and spring Q, but the bush P1 edge of the plate alternately pass over these ends E2 keyed on rocking shaft E3 and rod Ca1. As will slide past the head of screw P without depress- positive and negative currents are excited in soon as the feed box C is at rest over the mould D 1 ing it. The small spiral spring Q has for its the insulated wire surrounding the electrothe follower F with mould bottom plate F 1 (which object to support the bolt P with its nut wheel magnet. latter has till now been up level with the mould whilst spring Q is being depressed. table D) is lowered by follower cam G and levers H and H1 keyed on rocking shaft H2. The feed box C being slightly taper the material readily withdraws from it and falls with the follower to the bottom of the mould. The feed slide box now returns to box Z to be refilled, and on being withdrawn it carries with it the surplus material, wiping it off level with the mould table. The valve cam I through lever I and rod I2 will now shut off pressure from the hydraulic valve K and small lifting cylinder L and open the off-flow, whereupon the large cylinder B1 and faller blocks M will by their own weight drop, the latter entering the moulds D and compressing the material to a certain extent. In the act of falling, the large cylinder B1 will fill itself with water by suction through the pipe N, valve N 1, and pipe N 2, which latter communicates with a water supply tank. This tank is placed at a height of some feet perpendicularly above the press to ensure a more rapid filling of the cylinder B1. Whilst the cylinder B1 falls it will at the same time through the lifting rods L 2 which connect it with the ram L 1 force the water out of cylinder L through pipe L 3, valve K, and off-flow pipe K 1 into the supply and off-flow pipe N 2 of the large valve N 1. As soon as the faller blocks M are at rest upon the material, the valve cam O through lever O and rod 02 will shut off the connection of cylinder B with the water tank, and open the connection with the accumulator through pipe K, small valve K, pipe N 3, valve N1, and pipe N. After hydraulic pressure has acted on the material in the moulds during about a second, the valve cam O will shut off connection with accumulator and open off-flow in valve N 1, and almost immediately after this the valve cam I will shut off the off-flow in valve K and open communication from accumulator to lifting cylinder L. The ram L1 through the lifting rods L 2 will now raise the large cylinder B 1 to the position shown in the engraving, and at the same time force the water from cylinder BI back through pipe N, valve N1, and pipe N 2, to the tank. The follower cam G through levers H H1 and toggle joint H 3 will now raise the mould bottom plates, with finished bricks upon them to the level of the mould table D and immediately after the feed slide cam E, through levers E1E2 and rod C 1, will move the filled feed box C forward into the position shown, the finished brick being at the same time pushed by the feed box Coff the mould bottom plate F1 and on to a small platform Y fixed in front of the mould table D, from whence the bricks are now removed by hand, placed on a barrow, and conveyed to the place where they are piled up to ripen or set. The follower with mould bottom plate F remains up till the feed box C is at rest over it, when it is again lowered with the material for a new brick. With every revolution of the cam shaft all these operations are repeated and a brick made by each mould. The follower head F 2 is carried by the central vertical shaft F 3 passing through the The currents being conveyed to the receiving Fig. 4 represents one mode of regulating the instrument, induce rapid changes in the polarity feed in presses for giving pressure in an upward of an ordinary electro-magnet, between the poles direction only and in compound presses. The of which a small permanent magnet vibrates. Each hydraulic cylinder A forms part of press bottom vibratory movement of this little magnet effects piece. The spring Q is placed inside the cylinder the liberation of one tooth of an escape wheel, proA, and a chamber is formed in the bottom of the ram to admit spring Q and bush P1. The bolt Ppelled by a very light train of clockwork wheels passes through a stuffing box in the bottom of and main spring, and the axis of the escape wheel cylinder A. In this case the ram A 2 rests upon carries the hand or index of the dial. Thus as the the spring and is raised and lowered by it in the same manner as has been described with reference to shaft F3 in fig. 3. The spring must be strong enough to resist the hydraulic pressure upon the sectional area of bolt P, the hydraulic pressure being 10cwt. per square inch, and the sectional area of bolt P half an inch the pressure upon the spring is 5cwt. The portion of the ram above the chamber acts as guide to the shaft F 3, to the top of which the The shaft F3, is follower head F, 2 is screwed. raised and lowered and the set screw for adjusting the ranged in the same manner as described with reference to figs. 1 and 2. FIG. 2. Fig. 5 represents another modification for regulating the feed. The bolt P is secured to the bottom of cylinder A. The nut P2 for compressing and for easing spring Q is placed at the upper end of the bolt P, and the nut P 2 may reach up into a corresponding shaped recess in the ram A, or the bush Pis shaped to fit easy over the nut P2, and the bush is made with two or more projections which handle of the sender passes over the letters, positake into grooves in the ram, as indicated by dotted tive and negative currents are alternately induced lines. The ram in this case acts in place of the in the conducting wires, and these currents cause nut wheel S, described with reference to figs. 1 the hand of the receiving instrument to pass over and 2. For turning round the ram and thereby the same letters. By means of a small lever, tightening or easing spring Q, spokes R may fixed around the ram, or it may be provided with which is seen at the top of the dial of the receiving The instrument, the hand can be always set to zero on a number of holes for inserting a short bar. valves K and N 1, see figs. 1 and 2, are adaptations commencing the transmission of a message. of what are known as "Fenby's patent hydraulic slide valves," but other balanced hydraulic valves may be used. be In order to prevent accident in case the press should be started without material in the moulds, stops may be fixed between the fallers and the followers, or, in place of this, a separate hydraulic stop valve may be placed between valves K and N1, which when the cylinder or faller reaches a certain depth is closed by a tappet. Instead of the large valve N1 two separate valves may be employed, one large one for filling and discharging cylinder B when pressure is off, and a small one for admitting and shutting off hydraulic pressure. In order to reduce the friction of feed slide C in passing over mould table D and table D 2 the feed slide C is placed on four wheels C2 which run on the rails C3, figs. 1 and 2. WILDER'S MAGNETIC ALPHABETICAL TELEGRAPH. DECIDED improvement in magnetic telepress bottom A which acts as its guide in its rise A graph instruments has recently come under and fall. The upper part of shaft F 3 is slotted to The internal mechanism of the alarm bell, fig. 2, may be described as a train of clockwork wheels, which is set in motion by the electric current, and stopped after a while by an ingenious mechanical device. The action of the alarm bell is remarkably effective. The bell is rung loudly for a few seconds, and its ringing is accompanied by a movement which causes a red disc to appear at the opening in front of the case. The tell-tale disc shows when the bell has been rung to give notice of a message during the absence of the attendant. The arrangements for bringing the bell into, and excluding it from, the circuit are highly ingenious, and the whole apparatus constitutes a complete, simple, and effective system of telegraph communication, for which great credit is due to Mr. Wilder. No voltaic battery is required, and the instruments are so carefully constructed that they are not liable to get out of order. We are glad to be able to add that these instruments are now being made in large numbers by Mr. J. Sax, the telegraphic engineer, of 108, Great Russell-street, Bloomsbury, at whose show rooms we recently inspected the apparatus wo have been describing. RETURNS of the produce of the Austrian mining works have just been published by the Imperial Royal Statistical Commission, furnishing a good criterion of the deplorable state of everything connected with the national industry under former Governments. The total value of the mining produce for 1866 amounted to 40,468,861 florins, showing in comparison with 1861 a falling off of 4,000,000 florins, or 10 per cent. The iron trade seems to have suffered most severely, as the returns of the year 1866 show a diminution against those of 1861 of 42 per cent., and against 1862 of 60 per cent. of the value of 9,000,000 florins. In 1867 there was an total production of coal in 1866 was 48,000,000cwt increase of 4,896,710cwt., and the returns of the Several first five months of 1868 show a further increase The of 883,965cwt. on the returns for the same period of The movements of the handle are accurately reproduced by those of the The THE Theso | tar are gases, then follow water and ammoniacal' THE ARDSLEY OIL WORKS. products possessing a still gicator fxity. products vary in nature with the temperature te THE accompanying engravings are illustrative which the coal is exposed, and when it is distilled of the distilling apparatus used in the pro- at a red heat it yields a large quantity of gaseous duction of oil at the Ardsley Works. Before pro-and but a small amount of liquid hydrocarbons. ceeding to our description, it may not be out of The proportion of liquid products is much greater place to notice a few facts upon which the principle at a lower temperature. Coal-tar obtained from of distillation depends. When shale or coal is sub- the distillation of coal contains various basic submitted to distillatory treatment, the most volatile stances, including ammonia, aniline, diculine, portions at first escape, leaving behind substances chromoline, pyridine, toluidine, and others possessof continually decreasing volatility. As the opera-ing less importance. The acids include acetic and tion proceeds, and on an increase of temperature, rosalic, among others, but the principal acid is these are evolved in a gaseous form unchanged, or carbolic or phenic. resolved into more volatile matters and residual ] The first products from the distillation of the that as the light oils disappear from the still the It must be remembered remaining substances becomes more fixed, and a higher temperature is required for heavier oils. As the products increase in density, ereosote, or "dead oil," appears, napthaline and other solid products then become abundant, and the oil assumes a viscid state; the final residue consti |