tom, on each side of the window," (as shewn at letters a a, in my drawing,) a simultaneous motion is effected in the screws, by means of a bar extending across the bottom of the window," (see letters bb) "and connecting by bevil wheels," (see letter c,) "both screws with a winch handle, (d) by which they are turned. Upon the screws are fitted, nuts, (e) "to which are attached the shutters," (fff, which hook into each other,)" and, therefore, by the operation of turning the handle, the shutters are steadily and silently raised in front of the window, or lowered into their case."-Here ends the description as applicable to my improvements; but you further observe, in continuation, shat "the patentees mention some variations in the construction of this apparatus, such as endless chains passing over spiked wheels, instead of the screws for raising the shutters, or instead of the bars and wheels for transmitting the motion from one side of the window to the other." Now, in this last-mentioned plan, Mr. Smith is equally, or more, in fault than in the other; for he knows well, that it was tried at Messrs. Hankey's, and failed; and in consequence of such failure, was taken down, and the screw machinery, introduced by me, substituted in its place. The operation of the present apparatus having given unqualified approbation, Messrs. Hankey are now employing Mr. Thomas Thomas to fit up the remainder of the front of their premises in Fenchurch Street in a similar manner. The shutters for this purpose, are completed ready to put up, and may be seen in the manufactory of Mr. Thomas, (in Holland Street, Blackfriars,) to whom I have communicated fully my methods of constructing and manufacturing; and I have no hesitation in assuring the public, that there is at present no other person so competent, in every respect, to execute work of this kind. Your obedient Servant, JOHN MAC DOWALL. Observations by the Editor.-We have made a call at Mr. Thomas's manufactory, and examined the metallic shutters constructed for Messrs. Hankey, in which we cannot discover the slightest difference from those which we saw described in Messrs. Kitchen and Smith's specification. The security afforded by this admirable invention is such, as to entitle it to adoption wherever property is liable to the depredations of the burglar. Its operation is steady and uniform; and from its great simplicity and strength, it is almost impossible to be put out of order. The shutters being attached to the vertical screws by large nuts, it is evidently impossible to force them up or down, with any power that could be applied by burglars; while, by the application of a little winch inside the premises the operation of raising or lowering the shutters may be easily performed by a child. The great durability of these shutters renders them much more economical than those of wood, notwithstanding the first cost of the latter is somewhat less. EXPERIMENTS WITH STEAM-BOAT PADDLES. BY THE EDITOR. NOTWITHSTANDING the very numerous plans that have been proposed to improve the propelling apparatus for steam-boats, by substituting other machinery for the ordinary paddle-wheel, we do not hear of any of them being adopted. That a great loss of power is sustained, owing to the paddles entering and leaving the water at an unfavourable angle, when they are placed in the position of radii to the circle cannot be disputed, though its amount is variously estimated, and in reality they do very considerably under different circumstances; for, if the diameter of the wheel be very large, and the depth of immersion very little, the disadvantages mentioned are so trifling as to render the adoption of an apparatus that is more complex, less strong than the common wheel, by no means eligible. With the view of ascertaining whether the common wheel could not be improved, without materially altering the simplicity of its structure, we instituted some experiments a few days ago, which, we are happy to say, were attended with results so satisfactory, that we propose to renew and extend them, with apparatus on a larger scale. That which was employed in the experiments we are now about to describe, consisted of a kind of double boat, formed out of two solid pieces of wood, each about 30 inches long; they were shaped at the head and stern like a common coal barge, and were secured together, by nailing across the ends, on their superfices, two slips of wood, which kept them about 8 inches apart; into the recess thus formed between these two representatives of boats, were placed successively the models of five differently formed wheels, (shewn at plate VI. by figures 9 to 13.) They were made of tinned iron plate, and all of the same dimensions, namely, 7 inches diameter, 3 inches wide, and the paddles 1 inch deep. A tube was formed through the centre, for a moveable axis, which was, therefore, made common to them all; the ends of the axis turning in plummer blocks fixed to the inner sides of each boat. The power was applied by means of two weights descending from two pullies fixed in a frame above, the lines of which were wound round the axis of the paddles on each side, to keep the apparatus equipoised; a strong thread was attached midway between the sterns of the two boats, and the other end was wound upon a little reel. The trial was made upon a large basin of still water, on a calm day. The wheel, No. 9, in which the paddles are bent into right angles, and the sides inclosed being put on the axis, the weights wound up, and every thing carefully arranged to prevent, if possible, the error of a second of time, notice was given to let go; the weights, then descending, propelled the machine by the revolution of the wheel, which drew out 28 feet of thread in 37 se conds of time, before the weights had reached the lowest point of descent: this, it should be observed, was the mean result of three experiments, differing only in a very slight degree; which was a velocity equal to 45 feet per minute. Upon substituting the wheel No. 10, which has paddles of the same shape, but with the sides left open, as in the ordinary wheels, the average of three experiments gave 25 feet, 4 inches of space, travelled over in 36 seconds, which is equal to a speed of 42 feet per minute. In the wheel, No. 11, which has been applied to several steamboats, there is no other difference from the common wheel, except that the paddles, instead of being placed in the position of radii, are fixed at the angles shewn in the figure. The mean result of three experiments with this wheel, gave a speed of 45 feet per minute. The wheel No. 12 is the common wheel, without spokes, or radiating bars, the paddles being soldered to the tin plate; three experiments were made with this wheel, with scarcely any variation in the results, the mean of which was sixty-eight feet and a quarter per minute. The wheel No. 13 is the common wheel, left open, as usual, which averaged, upon three trials, a speed equal to 474 feet per minute. We were prepared to expect an advantage from enclosing the common wheel in the manner described; but the extraordinary 'increase of one-third in the effect never entered into our imagination. The result being of the highest importance to steam navigation, we have great pleasure in thus making it known to the public. It will be observed, that, in all the experiments, the quantity of power and of resistance were uniform, and therefore that no very important error could have been made. Had we not made the experiments ourselves, we should have been very slow to believe,; that, by this very simple and inexpensive alteration of the paddle-wheels, a boat, that is now propelled by her engines at the rate of 8 miles per hour, may make nearly twelve miles per hour! TEST FOR COTTON IN CLOTH.-At a late sitting of the Royal Academy of Metz, the following method of detecting the presence of cotton in woollen stuffs was communicated. An ounce of pure alkali is dissolved in half a pound of water, and in this the suspected stuff is boiled for two hours. If the stuff is of pure wool, it dissolves entirely, and forms upon the surface a soap, which will pass through a fine sieve; but if, on the contrary, the stuff contains cotton, or any other vegetable fibre, it will not be entirely dissolved, but will show itself when thrown into the sieve. GURNEY'S STEAM CARRIAGE. THE misrepresentations that have been put forth to the public, through the medium of the newspapers, relative to Mr. Gurney's steam coach, induced the Editor of this Work, a few days ago, to send a copy of the annexed Letter TO THE EDITOR OF THE TIMES. SIR-As a constant reader of your invaluable Paper, I could not have failed noticing from time to time, a succession of accounts relative to the experiments made with Gurney's steam carriage, as it is called, for if the accounts alluded to be true, it might as well have been called your's, Mr. Editor, or mine, and as I shall presently show, that it is any-body's and every-body's, Having been for many years the editor of a periodical work on mechanical science (the Journal of Patent Inventions), it may be presumed that I possess some knowledge of what has been done in matters of the kind; and this knowledge, however limited, has caused me to regard with surprise,, and even wonder, the impositions that have been practised upon the public credulity, relative to the steam carriage in question, by writers who betray an entire ignorance of the progress of improvements made in the steam engine, and of the various inventions of those ingenious men of the present day, who have given their attention to the construction of locomotive carriages. I am, Mr. Editor, an ardent adınirer, an absolute lover, heart and soul, of every thing connected with machinery, but above all with that noblest piece of mechanism, the steam-engine; and it is with delight that I anticipate the period when steam shall supply the place of horses, not only in propelling our carriages on the common road, but in drawing the plough and the harrow over the fields of the husbandman. If therefore I find fault with those writers who have heaped upon Mr. Gurney honours which do not belong to him, or who have ascribed inventions and discoveries to him, which were bequeathed to us by our fathers, or are the produce of living genius, let me not be suspected of a desire to damp the ardour of discovery, or to throw the slightest obstacle in the way of improvement. I am most ready to acknowledge that much credit is due to Mr. Gurney; he has persevered for nearly three years in making numerous experiments in locomotion, at an enormous expenditure of money; and now if the testimonies of his friends (Mr. Herapath, Dr. Wilkinson, and others, who have deluged the diurnal press with their communications), are to be relied on, it would appear by them that Mr. Gurney had abandoned all his own contrivances, and adopted those of others instead; receiving from his friends the most fulsome adulation for so doing, as if the inventions were original and extraordinary. It is likewise but fair to acknowledge that Mr. Gurney has done more in VOL. IV. NO. 75. 1ST OCTOBER, 1829. M public with steam carriages than any of his contemporaries, which I consider to be owing to his contemporaries not wishing to exhibit in public until they can do something better than Mr. Gurney has hithesto done; for I am not disposed to judge very favourably, of his experiments, when I perceive that all the accounts hitherto commnonicated to the newspapers have contained great misrepresentations of the facts, or they have suppressed some of those necessary data by which alone a correct judgment can be formed. These remarks particularly apply to the last statement that appeared in the Times, of the 8th instant, being a communication from Mr. John Herapath, of Cranford, which I am desirous of replying to, rather than such au incorrect statement should remain unanswered. That I may waste no more of your valuable space than is necessary to the exposure of the fallacy of Mr. Herapath's statements, and the defence of those numerous ingenious men whose inventions he has ascribed to Mr. Gurney, I shall pass over the prefatory observations and proceed to the examination of the "happy series of inventions," by which he asserts " Mr. Gurney has obviated all the obstacles opposed to the success and safety of his carriage." Now had Mr. Herapath not attempted to prove this assertion, he would not have exposed Mr. Gurney and himself to the ridicule of every mechanic and engineer in the kingdom; for it unfortunately happens, as I will take upon myself to shew most clearly, that not a single invention out of the whole of the "happy series," described by Mr. Herapath, had Mr. Gurney any more to do with the conception of, than Mr. Herapath had with the building of the temple of Solomon, notwithstanding he appears so desirous of passing for one of that great man's disciples, by his repeatedly reminding the reader of his mathematical investigations," and his " scientific researches." Well may Mr. Gurney exclaim," save me from my friends, I will take care of my enemies." " Having stated that the great practical discoveries of Mr. Gurney had completely confirmed his" (Mr. Herapath's) "scientific researches," he proceeds "to kill two birds with one stone," by telling us what the " series of happy inventions" consist of, and this explanation shews us at the same time, what was the nature of his "scientific researches;" for it must be quite evident to every informed person, that Mr. Herapath's researches in mechanism, have not been extended beyond the limits of Mr. Gurney's carriage. In that carriage he saw the inventions of Watt, and Hornblower, and Woolfe, and Trevethick, and Brunton, and Perkins, and Griffith, and James, and Hill, and Gordon, but knew them not ;-all was new to him; all extraordinary and peculiar, to" to this celebrated invention" yet the fact is demonstrable, that were the inventions of these men taken away, there would be nothing else left in the carriage, if Mr. Herapath's detail of them includes every thing; and I have no hesitation in saying, that nothing more, worthy of particular notice, was wanting to complete such a steam carriage as Mr. Gurney's is represented to be. Perhaps Mr. Herapath has been writing ironically |