288 ANSWERS TO CORRESPONDENTS. All communications should be addressed to the EDITOR of the ENGLISH MECHANIC, 31, Tavistockstreet, Covent Garden, W.C. The following are initials, &c., of letters to hand up to A. W. N. C-As a rule, we select queries that are likely to GRASPINGS AFTER KNOWLEDGE.-Mr. Hermann Smith, we tho G. R. L.-Your letter on "Health Helps" contains many MR. ROGERS-If you have any reliable information on the F. H. LINTON-Is a Russian coin of the Empress Anna, and E. H. C.-Too indistinct for illustration; probably an old F. W. G.-The congratulation should by right have a name 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 OUR ever obliging "F.R.A.S.," in a private note, says: "I T. P.-Your views are correct. The sol-fa system is not A NEW SUBSCRIBER.-See back numbers. A SIX MONTHS' SUBSCRIBER.-To the Registrar-General, 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. WORKING FOR THE LIFEBOAT.--I enclose you 2s. 6d, in W. on Pitman's Phonography next week. date. W. B.-You will see from a notice elsewhere that the day of publication will be altered without any alteration in the 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. AMANUENSIS -Send name and address. CAPT. PETERSON.-Another letter on the "Steam Lifeboat," T. GILLINGHAM.-Letter on the City of Boston much too ERRATA.-J. K. P." writes:-In my note on brass instruments, page 261, for "care" read "ease," and "gain" for "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 1494 H. O. M. Ximenes, Wargrave, Berks, and E. Betincourt 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 1407 E. Walbank, Leeds, apparatus to expedite the fitting of 1498 E. Leigh, Manchester, improvements in piles for engi- 1500 W. E. Newton, 66. Chancery-lane, improvements in earth 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-flelds. improvements in machinery or apparatus for making metal cop tubes.--A communication 1501 J. Yule, Glasgow, improvements in motive-power engines 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, improve- 15-7 R. H. Pounds, 1, Emmett-street, Poplar, improvements 1510 J. S. Starnes, 13 Broad-street, Ratcliffe, a new or improved 1512 W. R. Lake, Southampton-buildings, improvements in 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- 1519 A. M. Clark, 53, Chancery-lane, self-acting machine for 1521 R. C. Robinson, Preston, improvements in fire-grates 1523 G. Schuck. 13, Idol-lane, London, an improved machine 1526 J. Bullongh, Accrington, improvements in looms, warp- 1527 J. Bernard. Salisbury-street, Strand, improvements in blast and other furnaces, and in extracting metals from their ores and from metallurgical products 1529 J. Webster, Birmingham, improvements in converters for 1529 W. Horton, Sheffield, improvements in centre bits 1532 W. E. Newton, 66, Chancery-lane, improvements in looms 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 poses 1544 J. Henderson, New York, improvements in the process of refining and purifying cast iron for foundry and for other pur 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 1546 H. Blandy. Nottingham, improvements in the construction and arrangement of vessels employed in the manufacture 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 tion 1549 B. J. B. Mills, 35, Southampton-buildings, improvements 1551 H. A. Bonneville, 10, Sackville-street, Piccadilly, improve- 1553 W. E. Gedge, 11, Wellington-street, Strand, a new or im- tion 1551 W. E. Gedge, a new or improved plough.-A communica1558 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 1537 W. J. Schlesinger. Umon-court, Old Broad-street. improvements in producing rotary motion, applicable to egg heaters, churns, bottle washers, washing machines, drills. Lools and other instruments-A communication 1558 F. Tommasi, Paris, Boulevart de Strast ourg, 23, an improved therino press 1559 H. Bessemer, Queen-street-place. London, improvement, in the construction of steam ships and other vele employ t for the convevance 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 mes and apparatus for exhausting. forcing, and purifying gas Iheating and illuminating purposes 1561 S. H. Stephens, Grass Valley, California, machines for grinding, concentrating, and refining tin and other ores 1562 A. Manbre, Baker-street, improvements in appra applicable to the conversion of cereal and vegetable st into saccharine matter 1563 E. A. Strubin, Notting Hill, improvements in cameras reflecting and magnifying opaque ohjects-A communics a 1564 G. T. Leitch, Rutherglen, a new agricultural impleme 1565 W. T. Small, 13A. William-street, Holloway. impe ments in the method or methods of supply and exit of erase and other fluids, respectively to and from aquariums, test cisterns, and other like vessels 1561 A. M. Clark, 53. Chancery-lane, machinery for carrasy ting and moulding sheet metal. which improvements are mile applicable for other purposes.-A communication 1567 H. J. Collins, 15. 16. and 17, Bartholomew-close, impr ments in the manufacture of embossed fabrics in imitalia đ quilting 1568 . P. Williams, Great George-street, Westminster, in provements in railway switches or junction points 1569 C. D. Abel, 20. Southampton-building, Chancery-inne improvements in the manufacture of sockets and ferrules? wrought iron and other metals.-A communication 1570 C. D. Abel. improvements in the manufacture of wroacis metal tubes.-A communication 1571 C. D. Abel improvements in apparatus for drawing ta skelps.-A communication Hartford, 1571 W. Farin, Marseilles, improved apparatus employed in gymnastic performances an Connecticut. impro 1573 H. Bryant. some of Apparatus for illustrating the motions of heavenly bodies and explaining various celestial phenomen 1574 W. Beamish, 5, Elgin--road, Saint, Peter's-park, Paddi ton, constructing a cylindrical iron kerb for the recep repairing, and maintaining telegraph wires 1575 C. Mather, certain improvements in machinery L 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 machines — communication 1578 A. V. Newton, improvements in looms for weaving.communication 1579 L. Mignot. Boulevard de Strasbourg, 23, improved m chinery for making ice PATENTS SEALED. 3521 J. L. Booth, improvements in the manufacture of ralis for railroads 3508 J. Tongue, improvements in machinery or apparatus for sewing or stitching together the numbers or separate parta of a volume in the operation of book binding.-A communication 3622 E. Johnson, improvements in the arrangement and construction of granaries.-A communication 3675 G. T. Bousfield, improvements in the treatment of aromatic secondary monamines for obtaining colouring matter. -A communication 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 3724 H. E. Newton, improvements in traction engines.-A communication 48 W. Wield, improvements in machinery for winding yarn or thread on to bobbins 91 F. H. Knevitt, improvements in shutters and blinds for window's 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. jun., 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 3462 E. T. Hughes, manufacture of elliptic springs, and in apparatus employed therein.-A communication 8463 A. W. Pocock, improvements in meters or apparatus for measuring water and other liquids 3464 W. H. Willis, a new or improved apparatus for register. ing or indicating the points of games 3465 R. Acton and J. Mustard, improvements in machinery for feeding carding engines 3472 W. Spence, improvements in the manufacture of soda crystals 8173 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 3496 W.Tatham. 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 3688 E. Shakespear and G. Illaton, improvements in sewing 3895 H. Green, improvements in lubricators machines tion 1018 A. H. Brandon, improvements in looms.-A communica. 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 yara or thread upon conical surfaces 3523 W. Shanks, 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 3518 G. Preston and J. Prestige, improvements in apparatus for regulating the supply of water to waterclosets 3566 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 3025 J. Askew, refrigerator for cooling brewers' and dis. tillers' wort 3061 J. C. Martin, an improvement in the manufacture of finings as a substitute for singlass 3070 S. Butler, improvement in the manufacture of lace in twist lace machines 130 A. M. Clark, improvements in wooden parements and in cut the blocks therefor.-A communication Chatwood and J. Sturgeon, impro.ements in direct-noting, wer hammers 715 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 fingers upon them to exclude all light. This 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 employed by M. Plateau was as follows:-While one arising from the decomposition of white light, and 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 colour are capable of exerting their effect upon image of feeble intensity; this red spectrum was 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 his sight. Newton subjected his eye to the action of a great amount of concentrated light, by looking at the image of the Sun reflected from a mirror, and then turning his eye,when sufficiently fatigued, to an obscure corner of the apartment, he closed The experiments of Scherffer have decided that the eyelid and prepared to watch the result, when accidental colours are capable of combining and he saw a luminous image of the Sun, surrounded blending together precisely as objective colours; with coloured rings, which, growing weaker, by thus, the accidental blue and yellow form a green; degrees, finally disappeared. "I repeated this the red and blue, a violet, and so on. The method act a second and third time. At the third repe- of proceeding of Scherffer was exceedingly ition, when the luminous image, and the colours simple. He placed on a black ground small which surrounded it were rapidly disappearing, squares of violet and orange (the complemenand while my attention was concentrated in the taries of these being yellow and blue respectively), expectation that I should completely lose sight of and fixed his eye steadily first on one, and then them, I saw them, with no little surprise, again on the other without moving his head, till each make their appearance, and gradually become as had been examined four or five times. He then vivid and strong as they had been at the moment turned to a white wall, on which he perceived when I ceased contemplating the Sun." This ex-three squares in juxtaposition, coloured yellow, periment satisfactorily establishes the fact that green, and blue, the middle square being formed the retina, after having been excited by the action by the combination of the two accidentals, yellow of a luminous object, is gifted with the power of and blue. If orange and green had been the calling up a succession of coloured images that objective colours examined, violet would have have no real existence, but as the experiment been the colour of the centre square; in every case, performed by Newton is highly dangerous, and the colour of the mean would be a mixture of the likely to be attended with disagreeable results, colours of the two extremes. There is, however, we shall content ourselves with describing ex- one exception to this rule, which occurs when periments which equally well attest the active one of the objective colours is the complementary power of the retina to produce unreal images, and of the other; as, for instance, if red and green be which can be performed without danger or diffi- the two colours subjected to scrutiny. The culty. 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. 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 convintee us that two distinct phenomena are going 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 a luminous circular image, is not without its objections as a proof, and as an instance of the existence of this law, we will describe another experiment easily performed, and which dispels all doubt on the subject. Take two pieces of paper of about twenty inches square, each of which is coloured by an even tint of two different (the one red, and the other yellow, for example) colours, of as near as possible the same intensity, and cut the two squares in halves. Fix the four pieces of paper upon a piece of brown holland opposite to a window in such a manner that two edges of two differently coloured pieces of paper may be in contact, and at a distance of about ten inches suspend the two other pieces of paper each on the side of its own colour (these two exterior slips to serve for comparison). On examining carefully the entire arrangement, it will be seen that the two centre half sheets undergo reciprocally a modification of tint, and are no longer identical in colour with the separated sheets, but each has taken such a tint as would result from the original colour being tinged by the complementary of the colour of the other strip. In the example we have supposed, the interior red strip will tend to a violet colour, and the adjacent yellow strip to a green. M. Chevreul, to whose ingenuity we owe this decisive experiment, had abundant proof furnished him of the existence of this phenomenon in his official capacity as Superintendent of the Dyeing Department of the Royal Manufactories of the Gobelins, by the complaints of drapers who had given cloths of a single colour, red, violet, or blue, to have black figures painted upon them; on the red cloths appeared to them green patterns, on the violet cloths, greenish-yellow ones, and upon the blue, orange-coloured, instead of the black that had been ordered. In each case it will be noticed that the colour with which the black appeared to be tinged was the complementary of the colour on which it was painted. M. Chevreul covered up the groundwork of the cloth in such a way as to allow only the black to be visible, when the designs appeared as black as could have been desired, and the fault was entirely in the ignorance of the drapers to this law of simultaneous contrast. 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. If two 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. black or white screen which we have hitherto in a variety of cases. The knowledge of this fact is of great use 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 colour, it is of course slightly tinged with the If white be brought into contact with any be much enhanced, and stand out prominently complementary of that colour, but the colour from the neighbouring coloured surface. This employed becomes deeper and brighter. The will be the case, for example, if the exciting 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. 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 beautiful; they varied unceasingly, sometimes with inconceivable rapidity; the eyes were fascinated and the attention involuntary fixed on this magic tableau, equally enchanting and new. The clouds carried by the winds seemed each in its turn to bring an endless succession of different colours with the most harmonious tints." Yet this "magic tableau" was produced with the most simple apparatus; nothing more than two little apertures covered with coloured glass, suthciently removed from each other that the light of the Sun which passed through these coloured glasses might throw two distinct shadows of the same opaque body. Although the opaque body must be necessary to produce a shadow, the experiment can be varied to show the light tinged with the complementary of the surrounding coloured light. Meusnier vouches for the success of the experiment performed in the following portions, and be swiftly whirled round from the But if one of these sections be painted black, covered with the appropriate tint. Let us suppose colour. that consequently the image is increased, according as we refer it to a greater distance, waich ia 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 un the retina by the contemplation of a coloured ject, both during and after the action of a coloured rays. It seems most natural to suppos that after the organ of vision has been excita coloured light on the withdrawal of the cause excitement, the retina should gradually regain it normal state, which would occasion the perst ence of the primitive impression, growing feebler as the impression vanishes, yet without changing its nature, till, like the oscillatory motion of point of rest, when the reactionary property prependulum, it passes through its normal state, a duces 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 au 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 s not found except at a distance more or less corsiderable from the contour of that space, aud that this normal state is reached in passing through the effects of irradiation, and of the accidental then, we have presented to us two kinds of oscilcolours of the second (simultaneous) class." Here, lation, one of time and the other of space, which separately considered, are sufficient to explain all M. Plateau has pointed out "that they are conthe phenomena with which we are occupied, and nected with one another in the most natural manner-that they are simple consequences of the law M. Plateau does not absolutely of continuity." 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. of M. Plateau, and of M. Fichner, scarcely inWe cannot close this short article without expressing our sorrow and regret that the researches ferior to him in his enthusiasm, but less happy in misfortune. Too enthusiastic in their endeavour3 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. to produce these subjective colours, and analyse the sensations, they have been smitten with blindlieve 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 section of subjective colours, and for tearing sufficient to explain most of the phenomena pregreen tending to blue. This simple theory is away 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 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 action each mass of air is enabled only to give those kind of vibrating motion, but by means of external particular vibrations which are not opposed to the reaction from within.-OERSTED. 10 whatever extent you may be tempted to 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 under which it comes into existence or activity, easy under the forces that bear upon it-the greatest ease is its nature, becanse the inanimate has no will, no aspiration. A channel that is In the making of Oboes, art faithfully abides connected with a reed gives not its own tone, but by its traditions, and the same holds good in re- the tone resultant from the combination of itself spect of other typical instruments. In making with the reed; the offspring takes after both the channels designed for the several registers of parents. If the channel is deeper at the pallet the harmonium, we unfortunately have not the than at the reed, the tone will be very different same advantage of antiquity and of recognised to that given by a channel that is deeper at the models. Our art is as yet immature and un-reed end, or that arches in the centre. Even a defined, and present models are imperfect or but pipe 8ft. long, if only bowed the mere fraction of casually satisfactory. A little reflection will an inch more at the centre than at the ends, will show the difficulties inherent in our task. We give a perceptibly different quality of tone to that attempt to imitate an instrument of fixed type which will be produced from a pipe with perfectly which contains in one tube or pipe a whole parrallel sides. A fact of significence if you only range or compass of notes. In the harmonium consider it. we have a separate instrument for each note, each We have now to study the shapes to be given channel being virtually an individual pipe with to the channels of our soundboard, and you will an independent character and very independent readily gather that we place more value on the ways of showing it. In the original, one con-appreciation of the principles concerned in the formation of tube determines the whole series of structure of the harmonium than on mere arbinotes, each one growing out of the parsent stem trary measurements, which, whilst they wholly in due relation to the others. We, on the con- misled the learner, cannot fail to cause disaptrary, have to deal with dozens of distinct cuttings, pointment when results are tested. all of which have to be grafted and cultured into family likeness. The original has a certain length readily measured into correct divisions; we have only fractional representatives or 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 the precision which would yield us a referable standard. Incidental variations too minute for Remember and forget not the words of Oersted; thoughtfully considered they will help you over many a difficulty, and give a new interest to the facts that arise under your observation. Continuing the argument, we shall in our next chapter place before you several illustrations of the various forms of channel for characteristic registers. (To be continued.) nor afford to banish a single species. The form one may be considered as a distinct element in in the upper slot being stationary, and the one in flashing and smouldering in her hair. 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 character. We copy the form and mode of the chief solo instruments of the orchestra, and 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 influences which go to produce that sensible exisdifferent result. Do you ever consider that the tence in aërial 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 attainHere 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. Water tending to its level, the projectile pursuing its flight and sinking to 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 ment. the composition of forces in every given sound, of the over the combinations of the form will undubi tably exercise an influence in determining the The form of the sound? Yes, the expression is uncommon, no doubt, yet it is only the bare truth, and it is not altogether beyond the power of science to afford us glimpses of these shapes of air. Another time we may say something of "the theory of vortex atoms as bearing on our study, and of some beautiful optical demonstrato mind how the shapes of divergent water jets tions of sound; but at present we need only call are formed by the pipes whence they issue, how the courses of streams in their channels are resultant from combinations of force, how the surfaces of lake and ocean are marked with circles, intricately interlaced, and many patterned fringes of wave, all telling of contending or reciprocating activities let us watch these forms visible and palpable, and we shall have no plea for doubting that the invisible air, subject to the same laws, bears its rich tapestries and wondrous traceries of sound. We say of men, character displays itself; we have many proverbs that emphasise our belief in inherited virtues and vices, and the family like nesses that bespeak parentage and affect behaviour. In like manner, pipes, channels, and other musical agents, have predispositions which are always ready to display themselves. Each gives the tone that comes most natural to it, most 150. Traverse or to-and-fro motion. The pin the lower slot made to move in the direction of the horizontal dotted line, the lever will by its connection with the bar give to the latter a traversing motion in its guides a a. from horizontal rotating shaft. The mutilated 151. Stamp. Vertical percussive falls derived toothed pinion acts upon the rack to raise the rod until its teeth leave the rack and allow the 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 is formed to produce a uniform velocity of movegroove, in which the crank wrist works, and which ment of the wrist or reciprocating-rod. 155. The gyroscope or rotascope, an instrument illustrating the tendency of rotating bodies to preserve their plane of rotation. The spindle of the metallic disc, C is fitted to turn easily in bearings in the ring A. If the disc is set in rapid rotary motion on its axis, and the pintle Fat one side of the ring A, is placed on the bearing in the top of the pillar G the disc and ring seem indifferent to gravity, and instead of dropping begin to revolve about the vertical axis. 156. Bohnenberger's machine, illustrating the of three rings A A1 A2 placed one within the same tendency of rotating bodies. This consists other and connected by pivots at right angles to ball being set in rapid rotation, its axis will coneach other. The smallest ring A contains the bearings for the axis of a heavy ball B. The tinue in the same direction, no matter how the position of the rings may be altered; and the ring A3 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 B 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 by a hinge joint with the revolving frame H, so that variations in the inclination of the wheel A and fall. The frame H is driven by bevel gearwill cause the outer end of the piece B to rise ing from the engine, and by that means the Editor of the " American Artisan.” pinion I is carried round the stationary toothed | differs materially from the generality of alloys 158. Traverse of carriage, made variable by fusee according to the variation in diameter where the band acts. day. The gas referees appointed by the Board known as white metal, being harder, stronger, of Trade had to determine what should be the and soncrous; it is, in fact, as its name implies, maximum of sulphur compounds allowable in the a species of brass, and behaves like it under the gas of those companies under their jurisdiction, tool when bored or turned, and it is susceptible and, therefore, their proceedings were of the of a very high polish; at the same time it fuses greatest interest, not only to the public, but also at a lower temperature than ordinary brass, and to the gas managers. The referees had not yet can be melted in an iron pot or ladle over an ordi- issued any public report on the subject; but exnary fire. This renders it useful for fitting-up periments were in process, under the instructions engines and machines where first cost is an ob- of the referees; which, unquestionably, would ject, as it can be run into the plummer-blocks or throw much light on the point. Among others, 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 Northern Railway, with carriages running in the express train between London and Edinburgh, the axles being fitted with bearings of white brass at one end and ordinary brass at the other. These experiments were made under the direction of Mr. Sturrock, late locomotive engineer of the Great Northern Railway, who states that two bearings under No. 45 brake van, East Coast Joint Stock, diminished in weight 2oz. in running 161. Another simple form of clutch for pulleys, 19,400 miles, whilst the two brass bearings in the consisting of a pin on the lower shaft and a pin other end lost 2lb. 4oz.; that under No. 36, thirdon side of pulley. The pulley is moved length-class, E. C. J. S., the two white metal lost only wise of the shaft by means of a lever or other means to bring its pin into or out of contact with the pin on shaft. 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 flywheel gives a steady momentum to the drillspindle in its rotary motion. 160. Continuous rotary motion from oscillating. The beam being made to vibrate, the drum to which the cord is attached, working loose on flywheel 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 cover izbts since, Mr. P. M. Parsons, 24oz., against 1lb. 6oz. whilst running 20,000 MANAGEMENT OF GAS. T the seventh annual general meeting of the Atriti sento cintion of Gas Managers, on the 7th inst., at the rooms of the Society of Arts, more unsatisfactory than the present state of the maximum of sulphur to be allowed in the gas of the companies placed in their supervision. One of the questions referred to the referee had been to determine the burner to be employed in testing the gas for illuminating power. As appeared from their report, the referees carefully examined the various kinds of burners in use, and also some new ones. Their inquiries also revealed in an extraordinary manner the badness of the burners in common use. The investigation of the referees, as detailed in their report, showed that some of the burners gave barely 20 per cent. of the real illuminating powers. These facts prove in a remarkable manner that the fault had really lain with the consumers themselves, who have been in the habit of wasting the gas supplied to them, and throwing away large sums annually by the use of shamefully bad burners. 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 better burners. COCOA UNDER THE MICROSCOPE.* (Continued from page 175.) Woll proceed to the consid microscope for E now consideration of the the detection of adulteration of cocoa, those offered by chemistry having been already shown On examining a seed of cacao theobroma, we notice that it consists, like all seeds, of an outer membrane, or husk, enclos T conversazione of the Civil Engineers well known for his labours in the improvement ordinary coke scrubber, and it was a question of ordnance, sent samples of his white brass. whether iron could not be substituted advanExactly of what this very peculiar alloy consists tageously for coke. One fact, however, had re-in our last number. (says the Engineer) we shall not pretend to say. cently been ascertained-viz., that purification by It is unlike Babbit's or any other white metal scrubbing was not, after all, such a friend to gas with which we are acquainted, will not clog the managers as they had supposed it to be. The b', and has in practice proved very effective. It amount of sulphur in the gas varied from day to From the Food Journal. |