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A. W. N. C-As a rule, we select queries that are likely to evoke replies which may not only be useful to the querists themselves, but others similarly situated. Hence we prefer the information should pass through our columns. SILENT RUBBER will oblige by communicating the information to Mr S. V. Pocklington through our columns. JOHN C. SHEWAN.-We can't afford space or money for such illustrated corrections. GRASPINGS AFTER KNOWLEDGE.-Mr. Hermann Smith, who received a letter of inquiry which he has forwarded to us, says: "The writer has not given his name or address, as very likely he is ashamed of his poor writing, and so keeps dark. But I must confess those grasping after knowledge are to me as interesting as the most elegant language of well educated correspondents." We reproduce this sentence from Mr. Smith's letter because we thoroughly agree with him. G. R. L.-Your letter on "Health Helps" contains many good points, and some weak ones. It is, however, so jauntily put together that we have been obliged, reluctantly we admit, to discard it. MR. ROGERS-If you have any reliable information on the Western States of America in connection with emigration, we will put space at your disposal. F. H. LINTON-Is a Russian coin of the Empress Anna, and similar to Query 3860, replied to by " Bernardin,” p. 261. E. H. C.-Too indistinct for illustration; probably an old jetton or counter of the 14th or 15th century. D. D. BATTY (Manchester).-Many thanks. BERNARDIN. A classified list of all the vegetable oils, &c., would be a good subject for an article; also, on the modes of refining them. F. W. G. The congratulation should by right have a name and address. T. WARD. No stamps enclosed for advertisement. J. H. D. Should be glad of the articles on silver coins, with as many illustrations as are necessary. W. SCOTT.-We never send private addresses without the consent of the writer. OUR ever obliging "F. R. A.S.," in a private note, says: "I assure you I personally recommend the ENGLISH MECHANIC right and left to every scientific friend I have, and to others who, without claiming any title to that appellation, vet wish to know what is going on in the way of physical and mechanical discovery; and I am bound to add that I never made any recommendotion more conscientiously. It certainly seems to me that such a twopeuny worth as the MECHANIC must ultimately act as "Edexrerum,' and swallow up not only its so-called competitors, but the mass of our popular scientific serials to boot." THE Sixpenny Sale Column is the only place in which can appear queries sent by "Saepe," H. E. Turner. J. THOMAS.-You cannot obtain a specification until six months after the date of application for the patent. J. HAYWOOD (Barnsley).-They are quacks of the worst description. On no account send them more money, or you will lose it. If you really wish to try galvanism, apply to some respectable medical man, and he will recommend you a proper apparatus. T. P.-Your views are correct. The sol-fa system is not superior to the old notation. A NEW SUBSCRIBER.-See back numbers. A SIX MONTHS' SUBSCRIBER.-To the Registrar-General, Somerset House. Cost trifling. THOMAS SMITH.-See our advertisement pages. H. RAYNER.-The 68. edition has a key and also a, valuable appendix. We cannot recommend any book on the other subject named. TRAVELLER. Apply to any optician. J. W. BEDFORD.-The contributions you offer would be acceptable if up to the mark. VELOCE. You will find some information on the subject of rubber tires in the description of the Phantom" bicycle, In this number. LIVERPOOL READER-See Mr. Perry's advertisement on Vol. VIII., page 270. WORKING FOR THE LIFEBOAT.--I enclose you 2s. 6d, in stamps for the Lifeboat Fund, being 3d. per 100 on the orders I have got for label printing. As an amateur printer, I hit on this plan to raise funds for our boat, and to send more from this week's advertisement. I enclose you two or three specimens.-C. FORREST, Lofthouse, near Wakefield. W. on Pitman's Phonography next week. W. C. COLLINS.-Thanks for the kind offer. W. B.-You will see from a notice elsewhere that the day of publication will be altered without any alteration in the date. The ENGLISH MECHANIC will at the same time appear in new type. So we shall not only be stronger by the absorption of "Scientific Opinion," but, we hope, look better. AMANUENSI8-Send name and address. CAPT. PETERSON.-Another letter on the "Steam Lifeboat," T. GILLINGHAM.-Letter on the City of Boston much too dreamy for practical mortals. ERRATA.-J. K. P." writes:-In my note on brass instruments, page 261, for "care" read "ease," and " " for galo "jam" in my note on throttle valve, in same page. THE INVENTOR. IN obedience to the suggestions of a number of readers, we have decided on appropriating a portion of our space to a con densed list of patents as nearly as possible up to the date of our issue. APPLICATIONS FOR LETTERS PATENT DURING THE WEEK ENDING MAY 30, 1870. 1494 H. O. M. Ximenes, Wargrave, Berks, and E. Betincouri Boulogne-sur-Mer, improvements in hardening, preserving. and facing building materials 1495 J. Fletcher. 6, Bridgewater-street. Salford, improvements in coking and desulphurizing the coke after obtaining the gases, oils, and other products from coal 1496 E. A. Leigh, Manchester, improvements in shafting and in transmitting power 1407 E. Walbank, Leeds, apparatus to expedite the fitting of uppers" in all kinds of boots and shoes 1498 E. Leigh, Manchester, improvements in piles for engi neering purposes.-A communication 1409 H. B. Brook. Westminster, an improved medicinal compound or stomachie cordial 1500 W. E. Newton, 66. Chancery-lane, improvements in earth closets. A communication 1501 B. Hunt, 1, Serle-street. Lincoln's-inn, improvements in mechanism for fastening French or folding windows at any desired point when partially opened.-A communication 1502 A. Cochran, Kirktonfeld, Renfrew, improved apparatus for discharging water from steam pipes 1503 J. H. Johnson, 47, Lincoln's-inn-fields. improvements in machinery or apparatus for making metal cop tubes.--A communication en gines 1501 J. Yule, Glasgow, improvements in motive-power 1505 T. J. Mayall. Lifford Mills, King's Norton, Worcester, improvements in parlour foot-balls and other india-rubber articles 1500 W. R. Lake. Southampton-buildings, London, improvements in supporting apparatus for the rollers of spinning frames. A communication in ropes and cables 157 R. H. Pounds, 1, Emmett-street, Poplar, improvements 1508 L. Perkins, 6, Seaford-street. Regent-square, improvements in connections for fire-engine hoses and other pipes 1509 C. Tophain Coleman-street, Bunhill-row, improvements in certain parts of machines for mincing or minutely dividing meat 1510 J. S. Starnes, 13 Broad-street, Ratcliffe, a new or improved ventilator for the cabins, holds, and compartments of ships 1511 J. McNaught and W. McNaught, St. George's Foundry, Rochdale, improvements in machinery or apparatus for washing and drying wool, yarn. or other fibrous materials 1512 W. R. Lake, Southampton-buildings, improvements in washing machines.-A communication 1513 C. W. Siemens, 3, Great George-street, Westminster, improvements in regenerative gas furnaces and apparatus connected therewith 1514 G. Thomas, Colchester, improvements in the construction of gas stoves. 1515 J. W Horsfall, Camden Town, improvements in ventilating mines 1516 J. Falconer, New York, U.S. A., improvements in machinery for forming bats of wool for felting purposes.-A communication 1517 J. Shanks, Arbroath, wheels for traction steam engines and other heavy vehicles 1518 S. E. T. Steane, Barking, improvements in domestic fire escapes 1519 A. M. Clark, 53, Chancery-lane, self-acting machine for cutting wood screws and eye-bolts.-A cominunication 1520 C. E. Barton, 173. King Edward-street, Great Grimsby, breaking of ice for the preservation of fish and other purposes 1521 R. C. Robinson, Preston, improvements in fire-grates 1522 J. Appleton and R. C. Ross, Manchester, an improved process and apparatus for preparing and finishing printed paper 1523 G. Schuck, 13, Idol-lane, London, an improved machine for watering and sweeping streets.-A communication 1524 D. Jones, Clerkenwell, improvements in the manufacture and treatment of coal gas for illuminating purposes 1525 G. Lunge, South Shields. improvement in the treatment of esparto grass and other fibrous materials 1526 J. Ballongh, Accrington, improvements in looms, warping or beaming machines 1527 J. Bernard. Salisbury-street, Strand, improvements in blast and other furnaces, and in extracting metals from their ores and from metallurgical products 1528 J. Webster, Birmingham, improvements in converters for the manufacture of steel and other metals 1529 W. Horton, Sheffield, improvements in centre bits 1530 B. Cooper, Frome, improvements in looms for weaving 1531 J. Eastwood, Bradford, and H. W. Whitehead, Holbeck, improvements in machinery for combing wool, cotton, flax, and other fibrous substances 1532 W. E. Newton, 06. Chancery-lane, improvements in looms for weaving.-A communication 1533 W. Arnold, Barnsley, and W. Carnelley, Manchester, improvements in steam boilers 1534 L. Walker, and F. A. Walker, Liverpool, an improved setting fld 1535 W. Malam, New-road, Rotherhithe, an improved furnace or apparatus for consuming creosote and other hydrocarbons for the production of heat 1586 J. Bernard, Salisbury-street, Strand, improvements in the treatment of certain ores and metallurgical products, and in the extraction and recovery of their metals 1537 W. Astrop, Homerton, improvements in motive power 1538 A. Frerichs, Hamer Hall, Rochdale, improvements in machinery for spinning and doubling cotton and other fibrous materials 1539 J. I. Taylor, Manchester, improvements in washing, churning, and mixing machinery 1540 G. Zeller, 12, Great Prescot-street, Goodmans-fields, Middlesex, improvements in fire-arms 1541 W. Morgan, Rotherhithe, improvements in carriage axles and hearings 1542 R. Gammon, Warminster-road, Westbury, an improved railway sleeper for permanent ways 1543 J. Sellers, Preston, improvements in mileage indicators for vehicles 1544 J. Henderson, New York, improvements in the process of refining and purifying cast iron for foundry and for other pur poses 1545 P. G. B. Westmacott, Elswick, Newcastle-on-Tyne, improvements in apparatus for grinding or polishing plate glass or slabs of slate stone, marble or other substances tion and arrangement of vessels employed in the manufacture 1546 H. Blandy. Nottingham, improvements in the construc of nitrous oxide gas 1547 H. Rose, Albany-street, Regent's-park, improvements in the mode of attaching mineral teeth 1548 J. Dargue and W. Dargue, Bradford, improvements in machinery or apparatus employed in the process of bleaching, Scouring, dyeing, and sizing warps or yarns and fabrics 1519 B. J. B. Mills, 35, Southampton-buildings, improvements in safety attachments for steam generators.-A communica tion 1550 J. Cope, New North-street, Finsbury, an improvement in steam engines 1551 H. A. Bonneville, 10, Sackville-street, Piccadilly, improvements in breech-loading fire-arms-A communication 1552 H. A. Bonneville, a new and improved label holder and fastener.-A communication 1553 W. E. Gedge, 11, Wellington-street. Strand, a new or improved system of grooves for rolling and shaping iron or other metals. A communication 1551 W. E. Gedge, a new or improved plough.-A communication 1558 G. Stevens and J. Hendy, San Francisco, an electro-magnetic motor for sewing and other machines 1556 w. S. Moore, Percival-street. Goswell-road, an improvement in hand mirrors and other like articles 1657 W. J. Schlesinger, Union-court, Old Broad-street, improvements in producing rotary motion, applicable to exg beaters, churns, bottle washers, washing machines, drills. tools, and other instruments-A communication 138 F. Tommasi, Paris, Boulevart de Strash ourg, 23, an improved therino press 1550 H. Bessemer, Queen-street-place. London, improvemenTM, in the construction of steam ships and other vessels empiavoi for the conveyance of passenkers, and in the means and apparatus employed to prevent or lessen sea-sickness on board such vessels 1560 W. Cleland, Linacre, near Liverpool, improved massi and apparatus for exhausting. forcing. and purifying gas Eve heating and illuminating purposes 1581 8. H. Stephens, Grass Valley, California, machines grinding, concentrating, and refining tin and other ores 1562 A. Manbre, Baker-street, improvements in apparatz applicable to the conversion of cereal and vegetable auhalanm into saccharine matter 1563 E. A. Strubin, Notting Hill, improvements in camera) reflecting and magnifying opaque objects-A communes a 1564 G. T. Leitch, Rutherglen, a new agricultural impleme. 1505 W. T. Small, 13A. William-street, Holloway. impes ments in the method or methods of supply and exit of erase and other fluids, respectively to and from aquariums, tanti cisterns, and other like vessels 156 A M. Clark, 53, Chancery-lane, machinery for currat, ting and moulding sheet metal, which improvements are applicable for other purposes.-A communication 1567 R. J. Collins, 15. 16, and 17, Bartholomew-close, impro ments in the manufacture of embossed fabrics in imitaikos ɗ quilting 1568 R. P. Williams, Great George-street, Westminster, in provements in railway switches or junction points 1569 C. D. Abel. 26. Southampton-building, Chancery-ime improvements in the manufacture of sockets and ferrules wrought iron and other metals.-A communication 1570 C. D. Abel. improvements in the manufacture of wroak metal tubes-A communication 1571 C. D. Abel improvements in apparatus for drawing ta. skelps.-A communication 1571 W. Farin, Marseilles, improved apparatus employed in gymnastic performances 1573 H. Bryant. Hartford, Connecticut. an impro apparatus for illustrating the mottons of some of heavenly bodies and explaining various celestial phenomen 1574 W. Reamish, 5, Elgin--road, Saint, Peter's-park. Paddle ton, constructing a cylindrical iron kerb for the recept repairing, and maintaining telegraph wires 1575 C. Mather, certain improvements in machinery i apparatus used in sizing and dressing yarn 1276 J. F. Wiles. Sun-court, Cornhill, improvements u electro-magnetic engines 1577 W. E. Gedge, improvements in knitting machinescommunication 1578 A. V. Newton, improvements in looms for weaving.communication 1579 L. Mignot. Boulevard de Strasbourg, 23, improved m chinery for making ice 1580 H. Bessemer, Queen -street-place, London, improvement in the construction of stea ships employed for the out veyance of passsengers' luggag. nd cattle, and in the apparatus employed for such purpose on board ships, and for lessening of preventing sea sickness 3078 G. Ermen, G. A. Ermen, and W. Foster, improvements in the construction of brushes 3687 C. D. Abel, improvements in ploughs and cultivators for tilling the soil-A communication 8724 H. E. Newton, improvements in traction engines.-A 48 W. Wield, improvements in machinery for winding yarn or thread on to bobbins communication 91 P. II. Knevitt, improvements in shutters and blinds for windows 100 G. Kent improvements in rotary knife-cleaning and polishing machines 722 J. Moysey and C. Thorne, improvements in hackling machinery 776 W. Rainforth and W. Rainforth. jnn., improvements in rotary corn screens for dressing and separating grain 851 J. Bradbury, J. Bradbury, and J. Roberts, improvements in machinery for felting hat bodies 954 W. MacLean, improvements in printing, lithographing, and zin cographing 968 A. Barlow and J. Taylor, improvements in machinery or apparatus to be employed in preparing cotton or other fibrous substances for spinning 3451 T. Reissig, improvements in making a new derivative of phenol, and in producing certain colours therewith upon textile fabrics and yarns 3461 C. H. Hudson, improvements in cots or bedsteads, and guards to be attached thereto 346 E. T. Hughes, manufacture of elliptic springs, and in apparatus employed therein.-A communication 3463 A. W. Pocock, improvements in meters or apparatus for measuring water and other liquids 3464 W. H. Willis, a new or improved apparatus for registering or indicating the points of games $465 R. Acton and J. Mustard, improvements in machinery for feeding carding engines 3472 W. Spence, improvements in the manufacture of soda crystals 3173 T. G. Green, appliances for use in the manufacture of articles of earthenware and chinaware 3480 J. Peirce, improved compound machine for cutting tenons and mortises and sawing wood 3485 G. Hammer, improvements in cork-cutting machines 3488 A. Mitchell, improvements in caissons or apparatus to facilitate the building of bridge piers 3404 P. A. S. Langlois, and L. S. Thomassin, improvements in the manufacture of sulphuric acid 3495 E. Field, valves for steam fire-engine and other pumps 3490 W.JTatham. improvements in machinery for opening and breaking hard waste, rags of cotton, woollen flax, or silk, and for scutching and carding fibrous substances 3658 A. M. Clark, improvements in Jacquard apparatus.-A communication 3088 E. Shakespear and G. Illston, improvements in sewing machines 3895 H. Green, improvements in lubricators 1018 A. H. Brandon, improvements in looms.-A communica. tion 3477 J. T. Griffin, improvements in preparing, treating, and curing sponge to render it elastic and suitable for use as a stuffing for beds.-A communication 3488 F. C. Webb, improvements in the manufacture of submarine telegraphic cables 3499 J. C. Wilson, an improved revolving engine and pump 3507 J. Boyd, improvements in machinery for winding yarn or thread upon conical surfaces 3523 W. -hanks, improvements in machinery for forging shoes for horses 3541 J. H. Johnson, improvements in crucibles, melting pots, retorts, and furnaces,-A communication 3513 E. Edwards improvements in photo-mechanical printing 3548 G. Preston and J. Prestige, improvements in apparatus for regulating the supply of water to waterclosets 3560 J. Ballantyne, improvements in the manufacture of yarns Or threads 3585 W. I. Hetherington, improvements in motive-power engines, specially adapted for propelling ships 3015 W. E. Newton, improvements in harness for locms.-A communication 3621 E. Moss, improvements in kilns or apparatus for the manufacture of malt.-A communication 3625 J. Askew, refrigerator for cooling brewers' and distillers' wort 3061 J. C. Martin, an improvement in the manufacture of finings as a substitute for singlas8 3070 S. Butler, improvement in the manufacture of lace in twist lace machines 130 A. M. Clark, improvements in wooden pavements and in the blocks therefor.-A communication cut 711 ing Chatwood and J. Sturgeon, improvements in direct-notwer hammers The English Mechanic AND MIRROR OF SCIENCE AND ART. IN FRIDAY, JUNE 17, 1870. ACCIDENTAL COLOURS. on at the same time, namely, that which produces The researches of M. Plateau on this subject have led him to decide that the disappearances N our recent articles on "Colour and Colour of images do not vanish with a gradual and Blindness, it will be noticed that we have regular decrease of brilliancy, but are accomtreated merely of objective colours; that is to say, of panied with a succession of disappearances and colours that may be said to have a real existence, reappearances. The method of observation emarising from the decomposition of white light, and ployed by M. Plateau was as follows:-While one of his eyes was closed and bandaged, he directed in regard to which the eye is to be considered the other with fixed attention for a minute at simply as a passive instrument forming the organ least at a red paper, cutting off all extraneous of vision, and is in no way employed in the for-light by adapting a blackened tube of about fifty mation of the effect it witnesses. But under par- centimetres in length, and three in width, to his uncovered eye. When the eye was sufficiently ticular circumstances the eye itself is capable of fatigued, he turned his eye to the ceiling, without producing a certain degree of colour which has removing the tube, and without uncovering the no real existence, and is visible to the eye only as closed eye. On the ceiling, he saw projected a long as the circumstances that produce the unreal green circle, soon followed by a red circular image of feeble intensity; this red spectrum was colour are capable of exerting their effect upon followed by a green, which again gave place to the organ of vision. To these colours has been the red, and so on, the red appearing as often as applied the term subjective or accidental, and their four times, though of course gradually decreasing production is owing to a reactionary property in brilliancy. Notwithstanding Sir David Brewthat the eye possesses under the influence of light, ster's assertion that the manifestation of these more or less vivid, and which converts the organ phenomena are physically impossible in a perof vision into an active from a passive state. This fectly darkened room, the complementary image, reactionary power is well described in a letter and precisely the same appearances, can be profrom Newton addressed to Locke, in which he de- duced by closing the eyelids, and pressing the cribes an experiment performed at the peril of fingers upon them to exclude all light. This his sight. Newton subjected his eye to the action fact has required some modification of the hypoof a great amount of concentrated light, by look- thesis advanced by Brewster to account for the ing at the image of the Sun reflected from a mirror, phenomena, of which we shall say more hereand then turning his eye,when sufficiently fatigued, after. to an obscure corner of the apartment, he closed the eyelid and prepared to watch the result, when he saw a luminous image of the Sun, surrounded with coloured rings, which, growing weaker, by degrees, finally disappeared. "I repeated this act a second and third time. At the third repeition, when the luminous image, and the colours which surrounded it were rapidly disappearing, and while my attention was concentrated in the expectation that I should completely lose sight of them, I saw them, with no little surprise, again make their appearance, and gradually become as vivid and strong as they had been at the moment when I ceased contemplating the Sun." This experiment satisfactorily establishes the fact that the retina, after having been excited by the action of a luminous object, is gifted with the power of calling up a succession of coloured images that have no real existence, but as the experiment performed by Newton is highly dangerous, and likely to be attended with disagreeable results, we shall content ourselves with describing experiments which equally well attest the active power of the retina to produce unreal images, and which can be performed without danger or difficulty. If a red wafer be placed upon a white ground, as a piece of paper, for example, and be attentively examined for some time, there will be perceived around the wafer a ring of green, and if, after this, the eye be directed to a second piece of white paper, at the same distance from the eye as the first on which the red wafer was laid, an imaginary green wafer will be perceived of the same dimensions as the original red wafer, which will gradually grow fainter and finally disappear as the irritation occasioned by the red rays from the wafer gradually dissipates itself. This is the manner in which the experiment was effected by Buffon, but Scherffer has noticed that the accidental colour was both more brilliant, and the outline better defined if the natural colour was viewed on a black ground, and the eye afterwards transferred to a white. vice versa. If the wafer be of a yellow or blue colour, the eye, on being transferred from the natural colour, will see a phantom wafer of violet or orange; if it be black, the consequent object will be white, and Therefore this experiment makes us acquainted with the fact that the accidental colour arising from the prolonged contemplation of a natural colour is of a complementary hue, the term complementary being understood to imply two colours, which when blended together produce white. An attentive consideration of the simple experiment we have just described convincee us that two distinct phenomena are going The experiments of Scherffer have decided that accidental colours are capable of combining and blending together precisely as objective colours; thus, the accidental blue and yellow form a green; the red and blue, a violet, and so on. The method of proceeding of Scherffer was exceedingly simple. He placed on a black ground small squares of violet and orange (the complementaries of these being yellow and blue respectively), and fixed his eye steadily first on one, and then on the other without moving his head, till each had been examined four or five times. He then turned to a white wall, on which he perceived three squares in juxtaposition, coloured yellow, green, and blue, the middle square being formed by the combination of the two accidentals, yellow and blue. If orange and green had been the objective colours examined, violet would have been the colour of the centre square; in every case, the colour of the mean would be a mixture of the colours of the two extremes. There is, however, one of the objective colours is the complementary one exception to this rule, which occurs when of the other; as, for instance, if red and green be the two colours subjected to scrutiny. The centre square in this case is not white, but of a dark neutral colour, if projected on a white ground, and completely black if the eyes be closed. bject be yellow, and the coloured screen violet. Snch are a few of the properties of succedaneous subjective colours. Before we proceed to mention the cause of the phenomena we will add a few of the familiarities pertaining to simultaneous subjective colours. As we have already said, this is the name that physicists have applied to the accidental colour that is created during the contemplation of a coloured object. Many experiments prove beyond all doubt the capability of the eye to imagine colours while so occupied, and the simultaneous law of contrast is one of no little importance in the many trades and professions in which coloured decorations are employed, and the assortment of tints involved. As the coloured fringe, which we have described as appearing round the border of If two The researches of M. Chevreul on this subject are extensive and exhaustive. We shall merely mention here the conclusions to which his experiments and experience have conducted him ; they can all be deduced from the general enunciation of the law of simultaneous contrast. Since two accidental colours are capable of colours are in juxtaposition, of which one is the combining, it might be expected that an acci- complementary of the other, since each has the dental could be blended with a real colour, and tendency to overspread the surrounding space this is the case, which shows that accidental with its complementary tinge, the brilliancy of colours have all the attributes of real colours, ex- each must be enhanced, and the result must be cepting stability. The experiment to show this to produce colours of greater purity and brightcombination is easily effected by changing the ness. The knowledge of this fact is of great use black or white screen which we have hitherto in a variety of cases. considered to be employed as the material on For instance, the employwhich the accidental colour is projected for a co-ments is not desirable, since the effect of such a ment of red hangings and decorations in apartloured screen. If, for instance, the accidental red colour would be to give a greenish tinge to the arising from prolonged contemplation of the countenances of the inmates, and destroy the redobjective green be thrown on a blue screen, a brilliant violet will be the result. But it should furniture, giving it the appearance of oak or dish colour which is highly prized in mahogany be noticed, if the accidental red arising from the walnut wood. Judging from optical principles, same circumstances as detailed in the last experi- the head-dress that is best calculated to adorn ment, be projected upon a green screen the effect a fair complexion would be a green hat lined with will be simply to produce a neutral grey, of a rose-colour, because the rose-tint is reflected on dark tone, that is to say, in general terms, that the countenance, and is further heightened by when the accidental image is projected on a screen the complementary of the green overspreading of the same colour as the objective, the effect is the face. Undoubtedly, our example is a work simply one of obscurity. On the other hand, of supererogation, but it equally well serves our when the screen is of the same hue as the acci- purpose of illustration. dental, or the complementary of the natural colour, the brilliancy of the phantom colour will be much enhanced, and stand out prominently from the neighbouring coloured surface. This will be the case, for example, if the exciting colour, it is of course slightly tinged with the If white be brought into contact with any complementary of that colour, but the colour employed becomes deeper and brighter. The same result follows from the involuntary con trast of black, and any colour, and when black and white are in juxtaposition, the former becomes deeper, and the latter more brilliant than when viewed separately. The same modifications of colour take place, though less distinctly, when the two objects are not in contact, the alteration of colour becoming less as the distance between them becomes greater. portions, and be swiftly whirled round from the But if one of these sections be painted black, BILD INDIGO BLUE GREEN Simultaneous accidental colour manifests itself in another entirely different manner, but not less interesting, as is evidenced in Coloured Shadows, which differ from other accidental colours, which are difficult to perceive and eminently transitory, by their vividness and strongly-marked characteristics; "and the mind, however convinced of their unreality, repels with difficulty the notion that they are no simple illusions, no purely subjective appearance, but in truth real colours." These coloured shadows are produced with no great difficulty, and no very extensive apparatus. It is sufficient to interpose a body illuminated with white light between the coloured light and the screen on which the light falls, when it will be seen that the shadow is tinged with the colour that is complementary to the coloured light. For example, if we have a cone of red rays falling upon a sheet of paper, and an opaque body illuminated by white light be introduced in front of the paper, the shadow will be intensely green. Of course, by varying the colour, by means of a succession of coloured glasses, the shadow of the interposed object may be made to pass through all the varying shades of the spectrum. Count Rumford has been one of the most enthusiastic observers of this class of subjective colours; he expresses his admiration in no measured terms. "The shadows," he says, "were tinged with an infinite variety of colours, the most unexpected, and often the most beau- covered with the appropriate tint. Let us suppose tiful; they varied unceasingly, sometimes with that the colour is concentrated in the centre of inconceivable rapidity; the eyes were fascinated gravity of each sector, then, if any colour be left and the attention involuntary fixed on this magic out, the resulting light will be that colour which tableau, equally enchanting and new. The is nearest to the centre of gravity of the remaining sector. For instance, if Violet be painted black, or left out, the centre of gravity of the sector This line falls between will fall in the line a. this " magic tableau" was produced with the the Green (g) and the Yellow (y), hence the most simple apparatus; nothing more than two prismatic colours without Violet would combine, little apertures covered with coloured glass, suffi- and form a greenish yellow tint, in which the If green be left out the ciently removed from each other that the light of green preponderates. the Sun which passed through these coloured centre of gravity would fall between the red and glasses might throw two distinct shadows of the violet, which is the true complementary colour of same opaque body. Although the opaque body green. Hence, in all cases, the complementary of must be necessary to produce a shadow, the ex- line that bisects the arch it covers, to the opposite any colour can be determined by producing the periment can be varied to show the light tinged side of the circle, when the point at which it meets with the complementary of the surrounding the circumference will indicate the complementary clouds carried by the winds seemed each in its turn to bring an endless succession of different colours with the most harmonious tints." Yet coloured light. Meusnier vouches for the success of the experiment performed in the following colour. that consequently the image is increased, according as we refer it to a greater distance, which is in accordance with the fact. "We see no reason,” says he, "why it should be so on the hypothesis of a moral cause; the image should then always appear to us of the same magnitude as the object." This prefatory remark being admitted, it w be necessary to consider the effect produced us the retina by the contemplation of à coloured a ject, both during and after the action of a coloured rays. It seems most natural to sapp that after the organ of vision has been excita coloured light on the withdrawal of the cause (! excitement, the retina should gradually regain its normal state, which would occasion the pers ence of the primitive impression, growing feebler as the impression vanishes, yet without changing its nature, till, like the oscillatory motion of a pendulum, it passes through its normal state, a point of rest, when the reactionary property preduces the subjective image, which, when it has again reached the maximum degree of brightness, gradually tends to reproduce the primitive impression. All the phenomena that depend upon time, that is to say in which time enters essentially in order to produce the phenomena, are explained by this ingenious reasoning, and by an analogous reasoning, with reference to space, the phenomena of the simultaneous subjective colours are explained. "If while the retina is subjected to the action of the coloured light, we examine the parts of the organ which surround the place directly excited, we see that the normal state & not found except at a distance more or less corsiderable from the contour of that space, and that this normal state is reached in passing through the effects of irradiation, and of the accidental colours of the second (simultaneous) class." Here, then, we have presented to us two kinds of oscillation, one of time and the other of space, which separately considered, are sufficient to explain all the phenomena with which we are occupied, and M. Plateau has pointed out "that they are connected with one another in the most natural manper-that they are simple consequences of the law of continuity." M. Plateau does not absolutely deny the existence of the law of involuntary contrast, but he rightly doubts its competency to explain,all the circumstances that accidental colours present, and we think it will be admitted that where possible, it is better to trace the effect from physical causes than from moral, and that the reasoning of M. Platean is more satisfactory than that of M. Chevreul. manner:-In a room where the illumination is that the contemplation of a coloured object his deductions, have been crowned with a common effected by means of the solar light transmitted through a red curtain, the light of the sun passing through a small orifice cut in the curtain, and falling on a white screen, will not be white but green. We cannot close this short article without expressing our sorrow and regret that the researches of M. Plateau, and of M. Fichner, scarcely inferior to him in his enthusiasm, but less happy in misfortune. Too enthusiastic in their endeavour3 the sensations, they have been smitten with blindto produce these subjective colours, and analyse lieve M. Fichner recovered the use of his eye, but ness. Under proper medical treatment. we bethe illustrious Professor whose name has been mentioned so many times is thoroughly incapacitated from pursuing those inquiries, which have shed around his name an immortal lustre. A PRACTICAL TREATISE ON THE BY HERMANN SMITH. THIRD DIVISION.-CHAPTER IV We are now in a position to explain how it is developes in the eye a tendency to perceive a phantom object of a complementary colour, simply by supposing that the irritation occasioned by the red rays has to some extent destroyed the sensibility of the eye to red light, and that in the However difficult it may be to believe that we contemplation of a white light the eye is in preare deceived in the colour of these shadows, it is cisely the same position as in viewing the coloured by no means difficult to prove that we really are disc when the red has been omitted, when by the 80. We are indebted to Count Rumford for re- rule given above, the light emitted would be a moving all doubt, that attaches itself to this green tending to blue. This simple theory is section of subjective colours, and for tearing sufficient to explain most of the phenomena preaway the veil of mystery that surrounded them. sent in the succedaneous subjective colours, but He arranged his apparatus as usual, and made there are certain peculiarities of which it affords quite sure that the phenomena of coloured no competent and satisfactory explanation, such shadows were duly manifesting their peculiarities, as the production of subjective colours in comand attractions on the screen; he then proceeded plete darkness, and the combination of the accito examine these shadows through a blackened dental with the real objective colours. The first OF tube, that cut off all the surrounding light, and objection, as we have seen, was asserted by Sir left visible the shadow alone, and, lo! all the David Brewster to have arisen from a decided brilliancy and attraction of the phenomenon had physical impossibility; but M. Plateau, too long vanished, a colourless and obscure shadow was employed in these observations to be easily all that was visible, and the philosopher was deceived, has stated that he has seen such an convinced of the deception. The explanation of effect, and its existence is now so completely rethe phenomena of coloured shadows is to be cognised by physicists, as to require some modififound in a moral, rather than in a physical cause, cation of Scherffer's theory, for it is manifestly and the theories that account for subjective absurd to suppose that the insensibility of the eye colours will fail when applied to coloured sha- to a certain coloured light should in the absence of dows, and consequently considerable uncertainty all light, produce a complementary colour. attaches itself to this description of phenomena. Neither can this theory be held sufficiently to The explanatory theory suggested by Scherffer, explain the irregularity with which the accidental and accepted by Sir David Brewster, will, with a image vanishes, and the occasional reappearance slight alteration and addition, be sufficient to of the natural image. The ingenious theory of explain most of the phenomena that the subject M. Plateau seeks to evade none of these diffiof accidental colours produced. To make this culties. He begins by remarking that accidental sufficiently clear to our readers, it will be neces-images are due to a physical modification of the sary to refer, even at the risk of repetition, to organ, since the size of the accidental image is some of the well-known properties of colour. It considerably modified by the distance of the suris well known that if a disc of paper be painted face on which it is projected, from which it is to with the seven prismatic colours in certain pro-be inferred that the visual angle is constant, and author. THE masses of air which are enclosed in a pipe are not brought with the same ease into every possible kind of vibrating motion, but by means of external action each mass of air is enabled only to give those particular vibrations which are not opposed to the reaction from within.-VERSTED. 10 whatever extent you may be tempted to Tvestigate the nature of the harmonium, you will do well to take the sentence of the great Scandinavian philosopher as the fitting prelude to a thoughtful survey of the characteristic features of the instrument, and of the varieties of quality possible in its tones. The stops of the harmonium form a topic for critical discussion, and each speaker on his own showing professes to be a judge and connoisseur. Nothing is more common than the demand for a good oboe stop, a good clario *The copyright of this treatise is reserved by the net, trumpet, and violoncello, and other conceivable stops to fit the musician's fancy-nothing more common, unless it be the assertion that somebody possesses or knows somebody that possesses an instrument, harmonium or organ, with stops of so perfect a kind that the best judges could not distinguish their sounds from those of the genuine instruments with which they are supposed to compete. The extent of the delusion is the measure of the imperfect knowledge of the limitations of art, and of the lack of real acquaintance with the instruments brought into comparison. No professional artist would admit the claim for a moment, unless with a smile of condescension to the questioner. Imagine asking Barrett, or Puzzi, or Lazarus, or Piatti, how far they were deceived by the tones of organ or hormonium in the disguise of oboe, horn, clarionet, or violencello. The old ambition is rife as ever. The dream of the alchemists for an universal solvent, the quest of the Rosicrucians for the transmuting stone, trouble us no more, yet men after another fashion endeavour to pass through Nature's bounds, and all in vain. Our counterfeits pass with energetic warranty as quite equal to originals; but the true seer is never deceived; the fine royal mint-mark is beyond dispute, and makes visible its supremacy. We imitate wonderfully well the flavours of fruits, and the perfumes of flowers, yet our skill in chemistry is abashed in a moment in the presence of the simplest offering from orchard and garden; in all our attempts there is "a hidden want," and we are obliged to confess that Nature holds charms in her laboratory that we cannot match. In the same mood of thought we view musical instruments as under which it comes into existence or activity, easy under the forces that bear upon it-the we We have now to study the shapes to be given to the channels of our soundboard, and you will readily gather that we place more value on the appreciation of the principles concerned in the structure of the harmonium than on mere arbitrary measurements, which, whilst they wholly misled the learner, cannot fail to cause disappointment when results are tested. Remember and forget not the words of Oersted; thoughtfully considered they will help you over many a difficulty, and give a new interest your observation. or to the facts that arise under MECHANICAL MOVEMENTS.* (Continued from page 269.) have only fractional representatives multiples of such, and the various proportious of our channels, and the relations of each proportion to the whole have never yet been determined with standard. Incidental variations too minute for the precision which would yield us a referable accurate measurement yet powerful to influence Variations in length of channel, in depth, in width, in length the resultant quality of tone. and breadth of apertures for reed and pallet, in thickness or thinness of veneers, in scale of reed, in elasticity of swing in setting, and voicing, in in or pallet, in depth of keytouch, in covering Nature's work. The several classes of instruand enclosing, in strength and volume of wind, ments forming the modern orchestra belong to distinct types, and however we may vary these in and modifications of impulse-these and many grade and power, and increase their mechanical others, all more or less determine the character excellence, yet we cannot originate a new type, of tone of every register, and inasmuch as each nor afford to banish a single species. The form one may be considered as a distinct element in of each instrument, the mode of its musical the composition of forces in every given sound, excitation, and the range it can compass, these each variation we could name would count as a the horizontal dotted line, the lever will by its power controlling or disturbing the grouping and arrangement of the clustering spheres of aerial waves where of every sound is composed. The determine the characteristic tone by which we identify the species, and hence it will be obvious that if we depart from the type, and make new moulds after our own fancy, the natural results cannot possibly be the same. Our imitation may form of the motion, and the complexity of the 149.4 Another form of parallel ruler. The connected with an intermediate bar, by which arms are jointed in the middle and means the ends of the ruler, as well as the sides, are kept parallel. 150. Traverse or to-and-fro motion. The pin in the upper slot being stationary, and the one in the lower slot made to move in the direction of connection with the bar give to the latter a traversing motion in its guides a a. 151. Stamp. Vertical percussive falls derived from horizontal rotating shaft. The mutilated toothed pinion acts upon the rack to raise the be a marvellous good likeness, yet it would be sound, and whatever has power in least degree rod until its teeth leave the rack and allow the dangerous to our self-complacency to place it side by side with the original-our paste diamond lying in the effulgence of the one fair jewel flashing and smouldering in her hair. different result. Do not lightly allow this view to pass from your mind. Let it be firmly impressed upon you that the thorough comprehension of it is of essential value in the study of our instrument. Fixity of type ensures the reproduction of chief solo instruments of the orchestra, and the character. We copy the form and mode of the tones we listen to are the same in kind as those heard by our forefathers. The family likeness is recognised in every country where the art is practised. Take for instance the "Oboe" or "Hautbois." A tube of certain length, two reeds, a slender throat, slender as the throat of the nightingale, a pipe of conical bore, and apertures at definite distances, and the tone from such an instrument is of so unmistakeable a character that we identify it as belonging to a species, and call it for all time "oboe-tone." The form and the mode determine the product; alter these in any degree, and the result will inevitably be a Do you ever consider that the influences which go to produce that sensible existence in aerial waves which we call "tone" and "quality of tone" is as truly a compound of forces acting in definite relation, and stimulating the ear to recognition just as much as the food we taste and discriminate is a combination of chemical constituents in definite proportions? There is no chance in the result of any of these combinations, though there may be in our attempts at its attainment. Here the words of Oersted come in to our aid, and indicate why there is no chance. Nature in these, and we might as truly say, in all her movements follows the simple plan of taking the path of greatest ease. the projectile pursuing its flight and sinking to Water tending to its level, its rest, the planet tracing its orbit, all are seeking the line of greatest ease, under the composite and many-sided influences impelling and surrounding them. With as absolute a certainty, sound is generated according to the associated influences over the combinations of the form will undubi The form of the sound? Yes, the expression We say of men, character displays itself; we Each rod to fall. 152. Another arrangement of the Chinese windlass. The hammer helve is a lever of the first order. 153. A modification of the tilt or trip hammer. 154. A modification of the crank and slotted cross-head. The cross-head contains an endless 156. Bohnenberger's machine, illustrating the of three rings A A A placed one within the same tendency of rotating bodies. This consists other and connected by pivots at right angles to each other. The smallest ring A contains the bearings for the axis of a heavy ball B. The ball being set in rapid rotation, its axis will con tinue in the same direction, no matter how the position of the rings may be altered; and the ring A2 which supports it will resist a considerable pressure tending to displace it. 157. What is called the gyroscope governor, for steam engines, &c., patented by Alban B B1 of which is made in two pieces connected Anderson in 1858. A is a heavy wheel, the axle together by a universal joint. The wheel A is on one piece, B and a pinion I on the other piece B1. The piece B is connected at its middle will cause the outer end of the piece B to rise by a hinge joint with the revolving frame H, so and fall. The frame H is driven by bevel gearing from the engine, and by that means the that variations in the inclination of the wheel A * Extracted from a compilation by Mr. H. T. BROWN, Editor of the "American Artisan." rod P. 158. Traverse of carriage, made variable by fusee according to the variation in diameter where the band acts. 159. Primitive drilling apparatus. Being once set in motion, it is kept going by hand, by alternately pressing down and relieving the transverse bar to which the bands are attached, causing the bands to wind upon the spindle alternately in opposite directions, while the heavy disc er fly. wheel gives a steady momentum to the drillspindle in its rotary motion. MECHANICAL MOVEMENTS. pinion I is carried round the stationary toothed | differs materially from the generality of alloys day. The gas referees appointed by the Board circle G, and the wheel A is thus made to re- known as white metal, being harder, stronger, of Trade had to determine what should be the ceive a rapid rotary motion on its axis. When and sonorous; it is, in fact, as its name implies, maximum of sulphur compounds allowable in the the frame H and wheel A are in motion, the a species of brass, and behaves like it under the gas of those companies under their jurisdiction, tendency of the wheel A is to assume a vertical tool when bored or turned, and it is susceptible and, therefore, their proceedings were of the position, but this tendency is opposed by a spring of a very high polish; at the same time it fuses greatest interest, not only to the public, but also L. The greater the velocity of the governor, the at a lower temperature than ordinary brass, and to the gas managers. The referees had not yet stronger is the tendency above mentioned, and can be melted in an iron pot or ladle over an ordi- issued any public report on the subject; but exthe more it overcomes the force of the spring, nary fire. This renders it useful for fitting-up periments were in process, under the instructions and vice versa. The piece B is connected with engines and machines where first cost is an ob- of the referees; which, unquestionably, would the valve-rod by rods C D, and the spring L is ject, as it can be run into the plummer-blocks or throw much light on the point. Among others, connected with the said rod by levers N and framing to form the bearings, bushes, sockets, a systematic series of experiments was being &c., without the expense of fitting or boring made to ascertain the efficiency of each separate them, or it can be cast in metal moulds, or like part of the various purifying processes adopted ordinary brass or gun-metal, in sand or loam. in gasworks. The Chairman then alluded to a The white brass has been found by carefully-new apparatus devised by the gas referees for the conducted experiments to surpass in durability more efficient testing of the gas of the companies all other anti-friction metals against which it has for sulphur compounds other than sulphuretted been tested, and to prevent heating of the jour- hydrogen, and thought that its adoption should, nals. The durability of the white brass was as- in justice to the gas companies, be properly taken certained several years since by some very care-into account by the referees before they fixed the fully conducted experiments on the Great Nor- maximum of sulphur to be allowed in the gas of thern Railway, with carriages running in the the companies placed in their supervision. One express train between London and Edinburgh, of the questions referred to the referee had been the axles being fitted with bearings of white to determine the burner to be employed in testing brass at one end and ordinary brass at the other. the gas for illuminating power. As appeared These experiments were made under the direction from their report, the referees carefully examined of Mr. Sturrock, late locomotive engineer of the the various kinds of burners in use, and also Great Northern Railway, who states that two some new ones. Their inquiries also revealed in bearings under No. 45 brake van, East Coast an extraordinary manner the badness of the Joint Stock, diminished in weight 2oz. in running burners in common use. The investigation of 161. Another simple form of clutch for pulleys, 19,400 miles, whilst the two brass bearings in the the referees, as detailed in their report, showed consisting of a pin on the lower shaft and a pin other end lost 2lb. 4oz.; that under No. 36, third- that some of the burners gave barely 20 per cent. on side of pulley. The pulley is moved length-class, E. C. J. S., the two white metal lost only of the real illuminating powers. These facts wise of the shaft by means of a lever or other 24oz., against 1lb. 6oz. whilst running 20,000 prove in a remarkable manner that the fault had means to bring its pin into or out of contact with miles; and two under No. 35, E. C. J. S., third- really lain with the consumers themselves, who the pin on shaft. class, lost only 24oz. against 1lb. 12oz. of the have been in the habit of wasting the gas supbrass bearing whilst running 20,000 miles. The plied to them, and throwing away large sums bearings during these periods ran perfectly cool, annually by the use of shamefully bad burners. and were lubricated with oil. This was a point of great importance to the public, and it was to be hoped that the result of the publicity given to this report by the Board of Trade would be to lead consumers to adopt betier burners. 160. Continuous rotary motion from oscillating. The beam being made to vibrate, the drum to which the cord is attached, working loose on fly. wheel shaft, gives motion to said shaft through the pawl and ratchet-wheel, the pawl being attached to drum, and the ratchet-wheel fast on shaft. 162. Alternating traverse of upper shaft and its drum, produced by pin on the end of the shaft working in oblique groove in the lower cylinder. 163. See-saw, one of the simplest illustrations of a limited oscillating or alternate circular motion. (To be continued.) PARSONS' WHITE BRASS. Aheld to fee nizhts since, Mr. P. M. Parsons, T conversazione of the Civil Engineers MANAGEMENT OF GAS. A the seventh annual general meeting of the British Association of Gas Managers, on the 7th inst., at the rooms of the Society of Arts, Mr. Magnus Ohren, vice-president, in the chair, the Chairman, in the course of his address, referring to purification, said that nothing was more unsatisfactory than the present state of the COCOA UNDER THE MICROSCOPE. (Continued from page 175.) E now consideration of the Woll presentorded by the microscope for well known for his labours in the improvement ordinary coke scrubber, and it was a question the detection of adulteration of cocoa, those whether iron could not be substituted advan- offered by chemistry having been already shown tageously for coke. One fact, however, had re-in our last number. On examining a seed of ceutly been ascertained-viz., that purification by cacao theobroma, we notice that it consists, like scrubbing was not, after all, such a friend to gas all seeds, of an outer membrane, or husk, enclosmanagers as they had supposed it to be. The amount of sulphur in the gas varied from day to of ordnance, sent samples of his white brass. Exactly of what this very peculiar alloy consists (says the Engineer) we shall not pretend to say. It is unlike Babbit's or any other white metal with which we are acquainted, will not clog the b', and has in practice proved very effective. It From the Food Journal. |