Sir, The above sketch represents a plan of filter which has occurred to me, and appears likely to be of considerable service in some chemical manipulations. It is a long recurved tube, with a bellmouth of very shallow curvature; over this the filtering paper may be tied, supported within and without by a fold of book muslin. Whenever the fluid has been made to pass over the arch and out of the orifice below, the filter will continue to act as a syphon, and will exert an accelerating pressure proportionate to the length of the larger leg. It presents, also, a great advantage from the manner in which it will draw the fluid out of a vessel from above the sediment, and not through it, as in common cases. By adding another tube, and adopting an exhausting syringe, it could be used as a forcing filter. 1 have the honour to be, Mr. Editor, Your obedient servant, Φ. με Sir, It has not been remarked before, that the amount of friction is very great in a differential-crane, on account of the velocity of its parts. One way to diminish this velocity is to have the fixed and moveable pulleys as large as convenient, and to make the barrels that work the chain as small as possible. The shaft, on which the barrels and handles are fixed, must have large journals to stand the twist, &c.; and the great pressure on these journals, occasions most of the friction of the crane. The prefixed figure represents a plan of raising weights from a pit, in which there is every littl friction at these journals, because the pressure is taken off them by the weight A pulling the shaft up by the one barrel, and down by the other, while the small pin of the guide pulley B supports the weight. Any one, who has read my former letter on this subject, can see how to arrange the guide pulleys, to produce a similar effect in the plan there described. Q 2 228 HEATON'S IMPROVED METALLIC PISTONS. WINDOW-BLINDS. To keep passersby, and persons at a window opposite, fill up the slit. To persons interested, other, and perhaps more suitable, fashions will present themselves. I am yours truly, JAMES WHITELAW. Glasgow, May 16, 1834. from seeing what is going on in your house, and at the same time to darken it as little as possible, you must have the blinds made so as to wind upon a roller, placed under the wooden sole of the window, as in the accompanying sketch. If the friction is not sufficient to keep the blind at any height you want to have it, a small string, pressing upon either of the pulleys, will produce the desired effect. By having the blind to unhook at the ends of the cross-rod, light may be admitted at either one or both of its corners. A slit is to be left the whole length of the window-sole, for the blind to work through, and provision must also be made for taking out and putting in the roller. The fringe at the top of the blind may be drawn into the box at the window-sole, by giving the roller a turn or two, after the cross-rod is at the bottom, and then drawing the string as much back, to make the rod HEATONS' IMPROVED METALLIC PISTONS. Sir, I was greatly surprised at the communication of Mr. Barton, at p. 216 of your last Number. Had it merely contained the ordinary carpings of a narrow mind at the successful ingenuity of a rival, I should have permitted it to pass in silence. Mr. Barton has, however, made such groundless assertions, that I consider my own character for veracity at stake if I suffer them to go unnoticed. Mr. Barton commences, by stating, that he has no objection to my preference of Heatons' metallic piston, which as.. sertion is immediately contradicted by the whole tenor of his communication. Mr. Barton then complains that such preference is UNJUST. This, however, must be more logically proven before it can have any weight. Such an assertion is unjust on the part of Mr. Barton, seeing that all have an undoubted right to prefer what each believes to be best. The most extraordinary part of Mr. Barton's letter, however, is where he denies that there is any improvement in Messrs. Heatons' contrivance; and yet, in the same breath, claims for himself all the merit of the same. For, says he, "the very pistons, so highly lauded by your correspondent, were, in the first instance, made by me for Messrs. Heatons."!!! Now, sir, this is wholly untrue. Whether it was "the numerous individuals, competent to judge upon the subject," that caused this gross misstatement "to be made extensively known through the medium of your highly respectable and valuable publication," of course I know not; but, if they did, I must advise Mr. Barton in future to seek more sagacious counsel. I have been honoured with a letter from Messrs. Heaton, Brothers, on this subject, which I enclose for your insertion. In my description of Messrs. Heatons' piston (at page 134), I repre MR. RUTTER ON THE PHENOMENA OF FLAME. sented it as constructed with three segments; they are, however, usually made with four, but this in no way affects the beautiful principle of perfect equilibrium upon which they are constructed. In conclusion, I have only to say, that I am most truly sorry that a man so rich in mechanical talent and renown, as Mr. John Barton, should display so much envious feeling towards an ingenious fellow-labourer in the walks of science or attempt to support his claim upon any other basis than that of truth. Copy of a Letter of Messrs. Heaton, Brothers, to Sir, We observe in the Mech. Mag. of Saturday last a letter of Mr. Barton's, in which he states that the improved piston you had occasion to allude to some time since, was made by him for the Messrs. Heaton. Now, sir, we positively state, that neither Mr. Barton, nor any other person, has ever made a metallic piston for us; nor have we ever seen in any of Mr. Barton's pistons an elastic ring for the springs to act upon, similar to the one of ours described by you. We remain, Sir, Your humble servants, Shadwell-street, June 30, 1834. ON THE PHENOMENA OF FLAME-FURTHER Dear Sir,-A few days after you had published my communication on the phenomena of flame (Mech. Mag. 564), one of your anonymous correspondents (F. A.) kindly transcribed for me the greater part of a paper on flame, published many years since by Mr. G. O. Sym, in the Annals of Philosophy" (vol. viii. 1816, p. 321). About a week ago, another of your correspondents (Mr. Watson) very obligingly sent me the volume just mentioned, and also another volume of the same work (new series, vol. x. 1825, p. 447), containing a paper on the same subject, by Mr. J. Davies. Thus have I, very unexpectedly, had an opportunity of seeing, for the first time, what has been done by the gentlemen so honourably mentioned by Dr. Thompson, in this interesting department of 229 experimental science. Far from being discouraged at perceiving that a portion of the ground I have lately travelled over is pre-occupied, I rejoice to find that some of the results of my own independent and unassisted experiments are verified and supported, by a reference to such respectable authorities. It may justly excite our regret that so little appears to be known of these papers. Mr. Sym, who is long since gone to the grave, satisfactorily proved that flame is hollow. Mr. Davies advanced still farther, and demonstrated not only that the interior of flame will not support combustion, but that it contains no oxygen. To clear the soil of weeds is an employment equally necessary, although it may not be so honourable nor so satisfactory as that of casting abroad the precious seed on which depends the future harvest. The uprooting of error aids the development of truth in all its fair proportions. Important principles often lie concealed beneath an incrustation of absurd theories, the prejudices of antiquated habits of thought and expression, or the deformities with which vague speculation invests some of the most simple and the most beautiful ordinations of nature. Should it hereafter appear that I have assisted in clearing some of the difficulties out of the way of only one sincere inquirer after truth-thus facilitating his progress towards just conclusions respecting the nature of flame, I shall feel that I have obtained an adequate reward. In the process of combustion, "gas" and "vapour" is a necessary distinction. As I have never seen this insisted upon by any writer in any way that indicated an accurate conception of its importance, I hope I may be permitted to add a few "last words" in further elucidation of my views.* It would, I suppose, be hazardous to deny that every solid and liquid body may be made to assume the gaseous (vaporous ?) form, and that every gaseous (vaporous?) body may be reduced to a solid or a liquid. The terms gas and vapour, as ordinarily employed by us, do not possess a very determinate significa. *See Mech. Mag. 561, pp. 145, 146, § 43, 44, 45, 47, 230 REFRACTIVE POWERS OF THE ATMOSPHERE. tion. The bodies we denominate gaseous, on account of their continuing permanent in an aeriform state under certain conditions of temperature and pressure, of humidity or dryness, are nothing more than the particles of solid or liquid bodies in a refined and minutely divided form, and in combination with caloric. Vapours, in their popular acceptation, differ essentially from gases, inasmuch that they resume their original condition on the abstraction of a certain quantity of heat. May we not therefore view the separation of the particles in the former case as elementary, whilst in the latter it is mechanical? There is less difficulty in applying this principle to combustible bodies, with whose general habits we are somewhat familiar, than to others, as metals for instance, of which we know almost nothing as combustibles. That metals readily assume the vaporous form is sufficiently attested by the odour exhaled from some of them, especially brass, copper, ziuc, and arsenic, at very slight elevations of temperature. As in the disintegration of a metal during its combination with an acid, there is subdivision equivalent to that which constitutes the gaseous condition; so in the combustion of metals, as, for instance, iron wire in oxygen, or copper leaf in chlorine, we must admit that the energy exhibited, and the complete combination of the dissimilar elements, implies the transition of the metals, in either case, from the solid to the gaseous (vaporous?) state, previous to the reconstruction of a new substance, be it an oxide or a chloride. Whenever combustion takes place, we may rationally infer the chemical combination of dissimilar elements, and its sustentation depends upon the previous or the extemporaneous transition of the particles of bodies from the solid or liquid to the gaseous (vaporous ?) form. Specific temperature is a condition essentially necessary to combustion, whether it be of that kind which is lowest in the scale of incandescence, or that which exhibits the utmost intensity of heat, or brilliancy of light. That which we denominate specific temperature, may be, perhaps, nothing more than the excitation of the electrical energies of bodies. These brief allusions will sufficiently show that the terms gas and vapour, in their popular sense, are arbitrary distinctions; and that they do not determine, with philosophical accuracy, the precise nature of the bodies to which they respectively refer-vapour being, probably, the most correct definition of the elementary division of bodies when combined with caloric in the aeriform state, or during their transition in forming new compounds in the solid or liquid Dear Sir, state. I am very faithfully yours, Lymington, June 25, 1834. THE REFRACTIVE POWERS OF THE ATMO- Institution of Civil Engineers, April 15. "A conversation was held on the refractive quality of the atmosphere as affecting the taking of levels-an extract from the Memoir of the late Captain Joseph Huddart, relating to the subject, having been previously read. Captain Huddart had frequently remarked that low lands, and the extremities of head lands, forming an acute angle with the horizon when viewed at a distance, appeared elevated above the horizon with an open space between the land and the sea. These appearances he considered to arise from, and be in proportion to, the evaporation going on at the time, and felt convinced they were caused by evaporation; and that, instead of the refraction of the atmosphere increasing to the surface of the sea, it must decrease towards it from some elevated space; and that the principal cause which prevents the uniformity of density and refraction being continued, by the general law, down to the surface, is evaporation. He also conjectured that the difference of specific gravity in the particles of the atmosphere, may be a principal agent in evaporation; for the corpuscles of air, from their affinity with water, being combined at the surface of the fluid from expansion, form air specifically lighter than the drier atmosphere, and therefore rise, and become lighter as they ascend, until they become of the same density as the atmosphere. A member concluded, from the above statements, that the maximum of refraction was at the point most elevated from the surface to which evaporation extends, and consequently that a person MOREY'S VAPOUR LAMP. should be guarded in taking levels when elevated from the surface of a marsh or body of water during the process of evaporation. A member had frequently observed objects across the Thames come into view on the rise of the tide which at low water were hidden by the intervening land, this he attributed entirely to refraction, and considered that levels across a body of water should be taken as near the surface as possible. It was observed that this phenomenon was probably caused by the greater width of refractive medium; also, that long sights were to be avoided in taking levels after heavy rains; and that in levelling across a stream more accuracy would be attained by assuming the height of water equal at both sides, than by taking a sight with a spirit level."-Athe næum. MOREY'S VAPOUR LAMP. The Franklin Journal for May last contains the specification of a patent granted, in the United States, to Mr. Samuel Morey (a name already well known to the British public, in connexion with steam-engine speculations), for a lamp or apparatus for producing artificial light, constructed on a principle similar to that of Mr. Rutter's patent method of producing heat. We have no doubt this will prove a very valuable 231 invention, and as we understand there is an attempt making by certain parties (not Mr. Morey) to patent it also in this country, we hasten to publish the whole particulars, that all who please may make lamps for themselves, on this plan, without leave or license from the intended forestallers. Mr. Morey's Specification. This improvement consists of a metallic cylinder of such dimensions as may be desired, strong enough to bear a pressure of three or four pounds to the inch. In the centre of the top of this cylinder, there is co be a small tube inserted, about half an inch long, with a single hole in the upper end, of about from one-twentieth to one-sixtieth of an inch diameter. Round this small tube with a single hole, there is to be another tube an inch or more in diameter, and about an inch long, soldered to the top of the cylinder, having a cap that may be screwed on, or taken off; in the centre of which cap a screw may be fastened about one-eighth of an inch or more diameter. Around this screw, and in a circle, holes are to be made, about one-fiftieth or one-sixtieth of an inch diameter, and about one-third of an inch apart. A conical tube, about three inches long, and about three-fourths or more of an inch diameter, at the lower end, having a bar across near the bottom, with a hole and screw in the centre to fit that in the lower end of the conical tube. In the top of the cylinder a safety valve is to be affixed. It is then ready for use. To use it, put into the cylinder, through the safety valve, half a gill, or more, of spirits of turpentine, and about the same of water. Apply heat to the cylinder until the vapour issues pretty freely through the conical tube on the top. a flame is applied to that vapour, it takes fire, and burns with a beautiful white flame, like a gas-light. If there is any smoke, turn the conical tube on the top to the left, which will admit more air at the bottom to be mixed with the vapour in its ascent up the tube. As the vapour issues through the small holes in the cap, into and through the conical tube, by the pressure in the boiler, it will mix with, and carry along through the tube, in passing along, more or less air, in proportion to its velocity, by which means it is easy to make these lamps burn with all degrees of intensity, from that of a white flame and smoke, to that of a very intense white, to blue and white, and to that of all blue, and from that to perpetual explosion. These cylinders, which may be made to hold half a pint, or many gallons, it will be well to enclose in such a manner as to preserve If |