tachometer or stream gauge made by Mr. Robinson, optician, London, and is drawn to a scale of one-third of the full size. In this view ƒfƒ represents what may be termed a driving vane, which is acted on by the stream, and of which g is a plan. The plane of this vane is twisted, as represented by the dark shading in the cut, so as to present, not a knife edge, but an oblique face to the action of the current, which by inpinging on it, causes it to revolve exactly in the same way that the wind propels the sails of a windmill. On the spindle or shaft of this vane an endless screw is fixed at e, which works in the teeth of the first registering wheel, and causes it to revolve, when the vane is in motion and the screw in gear. Letters a and b represent a bar of brass, to which the pivots on which the registering wheels revolve are attached. This bar is moveable on a joint at ; and at the point a, a cord e is fixed, by pulling which the bar and wheels can be raised, and on releasing it they are again depressed by a spring at d. When the bar is raised, the teeth of the wheel are taken out of gear with the endless screw, and the vane is then left at liberty to revolve, the number of its revolutions being unregistered; but when the cord is released the spring forces down the wheels, and immediately puts the registering train into gear, in which state it is represented in the cut. Letter h is a stationary vane (which is shown broken off, but measures about 9 inches in length) for keeping the plane in which the driving vane revolves, at right angles to the direction of the current, and k is the end of a wooden rod to which the tachometer is attached when used. The different parts of the instrument itself are made of brass.

"The moveable bar for the registering wheels and the application of the cord and spring which have been described, afford the means of observing with great accuracy, in the following manner. The instrument having been adjusted by setting the registering wheels at zero, or noting in the field book the figure at which they stand, the cord is pulled tight so as to raise them out of gear, and the instrument is then immersed in the water. The vane immediately begins to revolve from the action of the current, and is permitted to move freely round until it has attained the full velocity due to the stream. When this is supposed to be the case, a signal is given by the person who observes the time, and the registering wheels are at that moment thrown into gear by letting the cord slip. At the end of a minute another signal is given, when the cord is again drawn and the wheels taken out of gear, and on raising

the instrument from the water the number of revolutions in the elapsed time is read off. This operation being completed in the centre of each division of the cord, the number of revolutions due to the velocity at each part of the very line where the cross section is taken, is at once obtained.

"Before using the tachometer, it is obvious that the value of a revolution of the vane must be ascertained; and although this is done by the manufacturers, it is proper that the scale of each instrument should be determined by the person who uses it, and that it be tested if the instrument has been out of use for some time, before being again employed in making observations. A scale sufficiently accurate for most hydrometrical purposes, (though not for the instrument when used as an anemometer,) may be obtained by applying it to some regular channel, such as a mill lead formed of masonry, timber, or iron, where the velocity is nearly the same throughout, and noting the number of revolutions performed during the passage of a float over a given number of feet, measured on the bank. In this way, it was found, by the mean of sixty-two observations, that each revolution of the vane in the instrument of which a drawing has been given, indicated the passage of the water over forty-six inches. The number of revolutions at several parts of the stream was ascertained to be the same in equal times, at both the commencement and the end of the experiments. This number, therefore, becomes in the instrument alluded to, a constant multiplier of the number of revolutions indicated by the vane; and hence, the number of feet passed over by the water in the given interval of time, is ascertained." Instruments for obtaining Water from different Depths.

"Instruments of various constructions have of late been tried for experimenting on this subject, by Scoresby, Sabine, and others; and as I am not aware that any work on marine surveying, or on surveying instruments, contains a description of such an apparatus, (to which I have applied the name of the hydrophore*,) the following account of two modifications of it, both of which I have been in the habit of using, may perhaps be instructive.

Fig. 1. represents a hydrophore used for procuring specimens of water from moderate depths, drawn on a scale of one-tenth the full size. It consists of a tight tin cylinder, letter a, having a conical valve at its top, b, which is represented in the diagram as being raised for the admission of water. The valve

ὕδωρ and φορεω.

is fixed dead or immoveable on a rod working in guides, the one resting between two Fig. 1.

307

is pulled, and the vessel is immediately filled with the water which is to be found at that depth. The cord being then thrown slack, the valve descends and closes the opening, and the instrument is slowly raised to the surface by means of the rod or rope, as the case may be, care being taken to preserve it in a vertical position. This apparatus is only applicable to limited depths, but will generally be found to answer all the purposes of the civil engineer.

The form of hydrophore represented in fig. 2, is used in deep water, to which the small one, just described, is inapplicable. Fig. 2.

uprights of brass above the cylinder, and the other in its interior, as shown in faintly dotted lines. The valve rod is by this means caused to move in a truly vertical line, and the valve attached to it consequently fills or closes the hole in the top of the cylinder, with greater accuracy than if its motion were undirected. A graduated pole or rod of iron, c, which in the diagram is shown broken off, is attached to the instrument, its end being inserted into the small tin cylinder at the side of the large valve or water cylinder, and there fixed by the clamp screws shown in the diagram. The bottom of the water cylinder may be loaded with lead to any extent required for the purpose of causing the apparatus to sink; but this, when an iron rod is used for lowering it, is hardly necessary. The spindle carrying the valve has an eye in its upper extremity, to which a cord is attached, for the purpose of opening the valve when the water is to be admitted, and on releasing the cord it again closes by its own weight. When the hydrophore is to be used, it is lowered to the required depth by the pole, which is fixed to its side; or if the depth be greater than the range of the pole, it is loaded with weights, and let down by means of a rope so attached as to keep it in a vertical position. Care must be taken, while lowering or raising it, that the small cord by which the valve is opened, be allowed to hang perfectly free and slack. When the apparatus has been lowered as far as is required, the small cord

It consists of an egg-shaped vessel, letter a, made of thick lead, to give the apparatus weight, having two valves, b and c, one in the top and another in the bottom, both opening upwards; these valves (which are represented as open in the diagram) are, to ensure more perfect fitting, fixed on separate spindles, which work in guides in the same manner as in the instrument shown in fig. 1. The valves, however, in the instrument I am now describing, are not opened by means of a cord, but by the impact of the projecting part d, of the lower spindle on the bottom, when the hydrophore is sunk to that depth. By this means the lower valve is forced upwards, and the upper spindle (the lower extremity of which is made nearly to touch the upper extremity of the lower one when the valves are shut) is, at the same time, forced up, carrying along with it the upper valve, which allows the air to escape, and the water rushing in, fills the

vessel. On raising the instrument from the bottom, both valves again shut by their own weight, and that of the mass of lead, a, which forms part of the lower spindle. The mode of using this hydrophore is sufficiently obvious; it is lowered by means of a rope made fast to a ring at the top, until it strikes on the bottom, when the valves are opened in the manner described, and the vessel is filled; on raising it the valves close, and the vessel can be drawn to the surface without its contents being mixed with the superincumbent water through which it has to pass. This instrument weighs about half a hundred weight, and has been easily used in from thirty to forty fathoms water in making engineering surveys, and could no doubt be employed for much greater depths, if necessary. It is represented in the cut on a scale of onetwentieth of the full size."

In an Appendix to the work, the author gives a useful Abstract of the Standing Orders of the Houses of Lords and Commons, with respect to Bills for making, maintaining, varying, extending, or enlarging Canals, Reservoirs, Aqueducts, Water Works, Navigations, Harbours, Docks, &c.

THE DOUBLE ACTING ROTARY ENGINE AFFAIR-AGAIN.

Since we plucked from the mock crown of this scheme, the only false gem that was likely to dazzle the public, the projectors have, with a very proper discretion, thrown it aside as a thing no longer of any use. A new prospectus has been put forth without the names of any persons as Directors. The only individuals who now appear as sponsors for the scheme are "Edward Lomax, Esq.," (the "eminent") who enacts the part of engineer," " and " Hyppolytus de Mancel, Esq.," who does that of " Secretary." Even the Count de Predaval, of the Austrian Imperial service, who was stated to be the inventor of the "double-acting" wonder of wonders, no longer figures-by name at least-on the scene. The "Patentee and promoters "that is to say, Messrs. Lomax and de Mancel, for and on behalf of the " patentee and promoters," whoever they may be, and whereever they may dwell, (Hanwell, Hoxton, or St. Luke's,) now"give notice that they are ready to contract for supplying

parties or companies with warranted double-acting rotary engines," at the following rates per horse power: "Stationary engines, acting by cold water or melted lead," 301., "mercury included" -"marine and locomotive engines acting by cold mercury, kept quite harmless," 40l. and 507. (the “melted lead" is a new feature-what it means we really have no idea.) Of these "ere trifles there is to be paid "one half on delivery, the other half three months after;" and lest any doubt should arise as to whether the " one half," and the "other half" make one whole between them, there is a positive assurance added, that the two halves mean "all included." Who can doubt of the willingness of the parties to contract on such terms for any number of engines they can receive orders foraye and to warrant them too? Engines equal to 1000 horses power (if of any) would not cost twice as many poundsso mighty simple a thing it is! but the "one-half on delivery" at an average of 351. per horse power would produce 35,000l., leaving a net sum in pocket of 33,000l.! Not, of course, to be run off with-that we are far from insinuating -but to constitute a guarantee fund, of which Messrs. Nobody, Brothers, and Co, or some other equally substantial firm, (yet to be appointed) will be the "bankers;" for of course" the company" will not think of making any dividends till "the three months after" have tested the worth of the machines delivered. But the order-the actual order-for the 1000 horses power-what likelihood is there of that? Not much, we should say, were the rationalities of the case only to be looked at in a rational spirit; but John Bull is notoriously an exceedingly gullible personage, and Messrs. Lomax, Hippolytus de Mancel, and Co., are persons of exceedingly imposing ways. In spite of our exposure of the gross absurdity of this " double-acting rotary affair-in spite of its palpable impracticability, we observe that Mr. Lon.ax persists in the new prospectus without directors, in assuring the public, "upon his professional reputation," that "the invention is an ingenious, practicable, efficient, and economical arrangement of machinery, founded on scientific principles, and an adaptation of the immutable laws of nature to the wants of man," &c. &c., and that Mr.

repeat (in the parrot style, which characterizes the whole of his book) the objections of Mr. J. Scott Russell to all rotary engines whatever, without attending to the fact that sweeping as these objections are, Mr. Russell admits that they resolve themselves more into difficulties of a mechanical nature (and therefore not impossible to be overcome) than into any absolute fallacy in principle.

The invention of the cylinder and piston Mr. Hoblyn ascribes to Newcomen and Cawley-only repeating again in this what others have said before him. If he will take the trouble to refer to the "Spiritalium," Art. xxvii., he will find that with regard to these, also, the toyman Hero had anticipated the Devonshire tradesmen by near two thousand years.

The subject of Steam navigation occupies a large space of Mr. Hoblyn's volume and deservedly so; but the proportion of that space, (nearly one-third) devoted to Mr. Samuel Hall's condensing apparatus (to say nothing of the doubleleads!) stands in strange contrast with the actual position of that invention at the present time. It looks more like a puff or advertisement done to order than any thing else. Mr. Hoblyn seems to be wholly unaware of the fact that the mode of condensation which he lauds so highly has, after full trial, been almost universally abandoned.

In an Appendix to his book, Mr. Hoblyn devotes about a dozen pages to the very relevant subject of "Causes and Prevention of slips or falls of Earth from the Slopes of Excavations on Railroads." What such things have to do in a "Manual of the Steam Engine," Mr. Hoblyn leaves his readers to guess. Had they been original, we should have concluded that they were intended to show that he could do something in that line,the manifestations to the contrary in the body of his work notwithstanding; but it so happens that they also are borrowed, and borrowed from a contemptible source which nobody else would think of quoting.

ON LIMES AND CEMENTS-MR. FROST'S EXPERIMENTS-COL. PASLEY'S TREAT

ISE.

Brooklyn, New York, June 1, 1841.

Sir,-It may be known to you, as well as to many of your readers, that some years ago I expended a vast deal of time and money in attempting to improve the

theory and practice of forming better limes and cements than were previously known, and that I fully succeeded in producing better limes, cheaper and better looking cements. But it may not be so generally known that I met with a circumstance as mortifying as it was vexatious, namely, that I could produce on a small scale, but never on a large scale, a cement exceedingly preferable to all others for architectural purposes, being of a fine white, or greyish white colour, while all other cements previously produced were of a very disagreeable, if not odious colour. From the chemical constitution of this cement, I know it to be also impenetrable, its hardness exceeding that of all others, none of which ever equal the hardness of good statuary marble, while I have specimens varying from three, to nearly six times the hardness of that expensive and beautiful material. This new cement, therefore, stood unrivalled in these several respects: First, it was imperishable in the air, or rather rain of London, which, loaded with carbonic gas, speedily destroys or dissolves all calcareous carbonates, as the marble statue of Queen Anne, in front of St. Paul's Cathedral, wearing its second or third head, effectually demonstrates. Second, it possessed immensely greater hardness. And third, it was perfectly plastic, a consideration as much beyond all computation, as the tedious and expensive labour of the statuary is to the rapid and inexpensive work of the modeller.

I have now the pleasure of informing you, that patience and science conquered the difficulty that so long opposed my attempts to produce this good thing on a large scale and at a cheap rate, and that I can send from this country white cement possessing all the properties before specified, or instruct any persons desirous of engaging in the manufacture in England, where the materials abound.

There have been many treatises written on cements in France, England, and other countries at various times; but a really good and comprehensive one remains yet to be written. All who have yet undertaken the task have taken much too narrow views of the subject, and it will be hereafter a matter of much wonder how the deuce, any of them could have been satisfied with the little they know about it.

It is but a few days since I saw Colonel Pasley's elaborate work on ce