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ANSWERS TO COKRESPONDENTS.

'.* All communications should be *<ldrcssed to the Editor of the Esolish Mechanic, 31, Tavlstockstraet, Covent Garden, W.C

THE INVENTOR.

lx obedience to the suggestion* of a number of readers, we have decided on appropriating a portion of our space to a con* den-ted list of patents as nearly As possible up to the date of our issue.

The following are initials, fee., of letters to hand up to rYiday morning, June 3, and unacknowledged elsewhere :— S. Ropers, Thos. Selhv, Rev. E. Kernan, T. S. W., G. R. S., Berero, Gimel, C. Wyndham, D. Wright. Constant Reader. J. Sbarpe. J. Harmon.C. Burgess, W. E. D., R. H. Harrison. H. P., Anxious Nephew, G. A. S., G. Prew, J. Gillingham. J. K. P., G. R. S., W.Drew, Sceptic. F.R.S.. W Butler, James Kemp. Hopeful. J. W. D K- W., h\. Lloyd, J. Thomas, J. E A.. L- &J., E. Bubb. B. W. R.,H. Garland. J. B. Tenby, F.R.A..S, Ab Initio, J. F. Sunt. Alfred Hancocks, C. de T., W. Binns. Contralto, E R. T., W. H , Beginner. J. C. ,S., W. J.C., Hyoerion. Jas. Grimby, Alwavs Welcome. J. T. Capt. 8. L., Pavne & Sons. Geo. Luff, W. H. E., W. JJ. R , Robert Touge, Messrs. Mscquard, George Smith. II. T. Vivian, Brother Reader, 11. Bolton, J. H. T., W. B.

A. W. X. C —As a rnle, we select queries that are likely to evoke replies which may not only be useful to the querists themselves, but others similar!} situated. Ifence we prefer the information should pass through our columns.

Silent Rchukr will oblige by communicating the information to Mr S. V. Pocklington through our columns.

John C. Shiwan.—We can't afford space or money for Buch illustrated corrections.

Grasfikgs 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 Bo keeps dark. But I must confess those grasping after knowledge arc 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—11 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 Isa Russian coin of the Empress Anna, and similar to Query 3860, reolied to by " Bernardin," p. 261.

E. H. C.—Too indistinct for illustration; probably un old jetton or counter of the 14th or 15th century.

D. D. Batti (Manchester).—Many thanks.

Bernardin.—A classified list of all the vegetable oils,

fee., would be a good subject for an article; also, on the

modes of refining tliem.

F. W. G,—The congratulation should by right have & name and address

T. Ward.—No stamps enclosed for advertisement.

J. H. I>.—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 r—" I asBure you I personally recommend the English MeChanic right and left to every acieniific friend 1 have, and to others who, without claiming any title to that appellation, yet 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 twopenny 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. Hatwood (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 lie 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 Kegirftrar-General, •Somerset House. Cost trifling.

Thomas Smith.—See our advertisement pagee.

H. Ratner.—The 6s. 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, n this numher.

Liverpool Reader.—See Mr. Perry's adve'tisenicut ou Vol. Viii., page 270.

Working Eor 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 ror our boat, and to send more from this week's advertisement. I enclose you two or three specimens.— C. Forrest, Loflliouse, near Wakefield.

W, on Pitman's Phonography next week.

W. C. Collins—Thanka for the k nd 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 absoiption of "Scientific Opinion," but. we bupe, look better.

Amanuensis —Send name and address.

Capt. Peterson.—Another letter on the " Steam Lifehoat," which was in type before yours came to hand, is inserted.

Electrical Discoveries.—Isham Baggsnext week.

Paul Gill.—Nothing in the letter.

T. Gillinoham— Letter on the City of Boston much too dreamy for practical mortals.

Errata.—"J. K. P." writes:—In my note on hriss intttrumentfl. page 261, far " care " read " ease," and " gaio " for "jam" in my note on throttle vulve, in same page.

APPLICATION'S FOR LRTrBK-* PATENT DURING TUB" WEEK ENDING MAY 30, 1870.

1404 II. 0. M. Xtmena*. Wargrave, Berks, and B. Betlncotirt Boulogne-aur-Mer. Improvements in hardening, preserving, nnd rocintt building materials

1405 J. Fletcher, a, Bridgewater-atreet. Salford. Improvement* in coking and desulphurizing theooke after vbtaining the sn'ea, oil*, and other product* from cot)

1408 B. A. Leigh, Manchester. Improvements in shaft in-* and in transmitting power

1407 B. W'albink, Leeds, apparatus to expedite the fitting of "uppers " In all kinds of hoot* *nd shoes

1498 E. Leigh, Manchester, improvements In piles for engineering purposes.— A communication

1400 H. B. Brook. Westminster, an improved medicinal com* pound or stomachic cordial

iron W. E. Newton, 08. Chancery-lane. Improvements In earth closets.—A communication

lVtl B. Hunt. 1, Serie-street. Llncoln's-lnn. Improvement* in mechanism for fastening French or folding- windows at any desired point when partlallv opened.—A communication

1503 A. Cochran. Klrktnnfleld, Renfrew, Improved apparatus for discharging water from steam pipes

1*03 J. H.Johnson. 47. l.incolr.'s-imi-Ilwld*. Improvements In machinery or apparatus fur making metal cop tubes.--A cumin on teat ion

1501 J. Yule, Glasgow, improvements in motive-power engines

IMS T.J. May all, LitTord Mills, Kfnir'a Norton, Worcester. improvements in parlour foot-balls and other india-rubber articles

1500 W. E. Lake. Southampton-buildings, London, Improvements in supporting apparatus for the rollers of spuininu frames.—A communication

ISO? K. H. Pounds, 1, Kmmett-street, Poplar, improvements in ropes and cables

150H L. Perkins, 3, Seaford-atreet. Regent-square, improvements In connections for fire-engine hones and other pipes

1509 C. Tophaio Coleman-stre*»r, Bunhill-rnw. improvements In certain parts of machines for mincing or minutely dividing meat

1510 J. S, Stames. IS Broad-«treet, Hatcllffe, a new or improved ventilator for the cabins, holds, and compart m»nt* of ships

1511 J. McNaught and W. McNaught. st. George's Foundry. Hochdale. improvements in ninchloery or apparatus for washing and drying wool, yarn, or other fibrous materials

1512 W. K~ T,ake, Southampton-hulldtngs, improvements In washing machines.—A communication

1513 C. VV. Siemens, 3. Gre.it George-«treot, Westminster, Improvements in regenerative gas furnaces and apparatus connected therewith

1514 G. Thomaa, Colchester. Improvements In the construe* tion of gas stoves.

1515 J. W HorsfaU, Camden Town, Improvements in ventilating mines

l.MlfJ. Falconer, New York. U.S A., improvements in machinery for forming bats of wool fur felting purpose*. —A communication

151" J. Shanks. Arbroath, wheels for traction steam engines and other heavy vehicles

1518 8. E. T. Steane, Barking, Improvements In domestic Oreescapes

1510 A. M. Clark, 53, Chancery-lane, self-acting machine for cutting wood screws and eye-bolts.—A communication

L'.iWO. E. Barton, 173. King Kdward-street, Great Grimsby, breaking of ice for the preservation of fish and other purposes

1531 R.C. Robinson, Preston, improvements in fire-grates

1522 J. Appleton and K.O.Ross, Miuchester. an improved process and apparatus for preparing and finishing printed paper

1523 G. Schuck. 18, Idol-lane, London, an improved machine for watering and sweeping streets.—A communication

1524 I). Jones, Clerk on well, improvements in the manufacture and treatment of coal gas for illuminating purposes

1525 G. Lunee, South Shields, improvement in the treatment of esparto grass and other fibrous materials

1520 J. Bnllougb, Accrington, Improvements In looms, warping or beaming machines

1527 J-Bernard. **alisbury-street. Strand. Improvements In blast and other furnaces, and In extracting metals from their ores and from metallurgical products

152*! J. Webster, Birmingham, improvements in converters for the manufacture of steel and other metals

1520 W. Horton, Sheffield, improvements in centre bits

15(0 B. Cooper, Frotne, Improvements in looms for weaving

1531 J. Eastwood. Hradford. and H. W. Whitehead. Holbeck, improvements In machinery for combing wool, cotton, flax, and other fibrous substances

1592 W. E. Newton, 00. Chancery-lane, Improvements In looms fur weaving.—A communicUlou

1533 W. Arnold, Barnsley. and W. Carnclley, Manchester, improvements In steam boilers

1534 L. Walker, and F. A. Walker, Liverpool, an improved setting fid

1535 W. Malam, New-road, Rotherhfthe. an Improved furnaco or apparatus for consuming creosote and other hydrocarbons for the production of heat

1538 J- Bernard. Salisbury-street.Strand,improvements In the treatment of certain ores and metallurgical products, and in the extraction and recovery or their metals

1637 W. Astrop, Homerton, improvements in motive power

1538 A. Prerichs, Hamer Hall, ltochdale. improvements in machinery for spinning and doubling cotton and other Ithroua materials

1539 J. I, Taylor. Manchester. Improvements in washing, churning, and mixing machinery

1540 G. Keller. 12, Great Prescot-stroet, Goodmans-Holds, Middlesex, improvements in fire-arum

1541 W. Morgan, Uotherhithe, improvements in carriage axleARnd bearings

1542 it. Gammon. Warminster-road, Westbury, an improved railway sleeper for permanent ways

1543 J. Sellers, Treston, improvements in mileage indicators for vehicles

1544 -I. Henderson, New York, improvements in the process of refining and purifying cast irou for foundry and lor other purposes

1515 P. G. B. Westmacott, Elswlck. Newcastle-on-Tyne, Improvements in apparatusfor grindlugur polishing piato glass or slabs of slate stone, marble or other suhxtancej

1540 H. Blandy. Kottinghatn, improvements in the construction and arraugement of veasels employed m the manufacture or nitrous oxide gas

1547 H. Ko*e. Alhany-street. Reguit's-park, improvements In the mode of attaching mineral teeth

1548 J. Darguoand W. Dargue. Hradford, Improvements in machinery or apparatus employed in the process of bleaching, scouring', dyeiiiK. and (sizing warps or yarns and fabrics

1549 B.J. It. Mills, 55. Southjimpion-huildlngs. improvements In safety attachments for steam generators.—A communication

1550 J. Cope, New North-street, Pinsbury, an improvement in fct'-am engines

1551 H. A. Bonneville. 10, Sackville-stroet, Piccadilly, Improvements In hreech-loaaing fire-arm*.—A communlcat.on

1552 H. A. Bonneville, anewaud improved label holder and fastener.—A communication

1553 W. E. oedge, li. Wellington-street. Strand, A new or improved system or grooves Tor rolling and shaping iron or other inelals.—A communication

1554 W. B. Gedge, a new or Improved plough.—A communication

1558 G. Rtevens and J. Hendy, San Francisco, an electro-magnetic motor Tor sewing and other machine*

15M w. S, Moore, Porcival-stree.t, Uoswejl-road, an improvement in hand mirrors and other Ifkn articles

1557 W. J. Sciiiesinger. Union-court, Did Broad-street, improvements in producing rotary motion, applicable to egg heaters, churns, lioltlo was hers, washing machines, drills, it oln and other instrument*.— \ commiihlcutinn

1555 K. Tommasl, Paris, Uoulevnrt de Stras* ourg, 23, an improved theriuopreBi

15*9 H. Bmbctbt. Queen -street-place. London, taigr«»«'fsn«>»» In the oonstrunMon of atctm *lpp« *nd other *-—M* «rmp-lov•»)' tor the conveyance of paas*n*cv«, and In lb* oasia^La tat apparatus employed to prevent or le^cn »e«-sieiioa»» a« bAarf such veasels

1500 W. Cleland, Llnacre. near Liverpool, impmrod meat-1 and apparatus for exhau«tlng. rorelng. and panfyita- gaa I .heating and illuminating purpo«*>t

1501 9. H. Swphsni.Gra^s Talley, PiJironita, mavohinie* tgrtnding, ooncentraHng. and refining tin and otker or**

1503 A. Manbre. Baker-street, improvements in nj>raLrmt-x applicable to the conversion ofcerearand teg*table «iia«u&> inm saccharine matter

1501 E. a.Struhin.Nottlnc Hill. Improvement* in camersjiv reflecting and ipaimifrtng opaque ohj^cta—\ Momunm^

1544 G. T. l^eitch. Knthergian. a new asricultnral iropleasee

1S83 W. T. Hmall, 18a. Wi|lfam-str*»et. Holloway. irrjp«-;.^ ments in the method or methods or supply and eiit «f »air and other fluids, respectively to and from ayiia.rlu.ms, taali ciMterriH, and o-her like vessels

158i A M.Clark. 53, Ch*nc>r,v-]ane, maehinery for r*rnr, tins-and moulding sheet metal, which imp'owemeats aj> a*a applicable for other purpose*.—A commnnicsvtlnn

1507 K.. J, Collins, 15. 10. and 17. Bartholomew-doe*, impf^ menisinthe manufacture of embossed rabric* lu imitaai-si t quilting

1508 K. P. Williams. Great Qeorge-street, Weatmbxat^r. m provemeuts in railway switches or junction points

1500 C. D. Abel. 20. Southampton-buildings. ChanoM-r la-improvements in the manufacture of sockets and. tTcrrula -■ wrought iron and other metals.—A communication

1570 C. D. Abel, improvements in the manufacture of vroat^ metal tubes —A communication

15H O. D. Abel imorovementa in apparatus for drawing ti. sk«lps.-A communication

1372 W Partm, "ar-'-llles. improved apparatus l* . employed in gvmiifistlcperrormancas

1373 H. Hryant. Mart ford, Connecticut, an impr*apparatus for illustrating the motions or lomn of h. heavenly bodies and expUUiinsi various celostial pheuo.m#r»

15,4 w. Keamish.5, Klgin--ro*d, ^aint. Peter's-povra;. Pavd4»n. ton, constructing a cylindrical trm kerb for the r« ceni;repairing, and maintaining telegraph wires

1575 O. Mather. corUin improvements in machinery i ai-paratus us-d in sizing and dresking yarn

1279 J. F. Wiles, sun-court. Cornhill, improvements a electro-magnetic engines «•««*■

1577 W. E. Gedge, Improvements In knitting machine*communication

1578 A. V Newton, improvemenU In looms ror weavingooinmunicatlon ■■*»*

1579 L Mignot. Boulevard de Strasbourg, 33, improved o ■ chlnery for making ice

ltwoH. Bessemer. Queen-street-place, London, improvement In the construction of area aMn« employed for the. rs,,. % eyanee nrp isssengers' luggag- nd cattle, and in the mpn^rat ■ * employed Tor such purpose on board ships, and for lessening ojpreventing sea sickuesn

fll r . „ PATKNTS SEALRTX

IHl J. L. Booth/Improvements In the manufacture »rnu> ror railroads

8598 J -,. Tongue, improvements In machinery or appseafti* ror sewing or etttehlnv together theimmbert orwpctfe ?,*rtJ ui.i volume in thu operation of bookbindlng.-A eom«fuiic»tK>n

8823 K. Johnson, lmprovmenta in thu arrangemeflt saa con•tTMotlon or granarlea.—A communication

3»r/5 G. T. BVmsfleld, improvements in the treatment of aromatic secondary monamines forobtftiiiincwlourluje matter . — A communication

M78 G. Ermen, u. A. Ermen, and W. Fostsr, \myroveraenta In the construction or brushes

t,S*7 9^U-A!**1-'mProv*mentBinpIoughinuid cultivators ft* tilling the soil—A communication

3724 H. E. Newton, improvements in traction englnes--A communication

48 W. Wield, improvements In machinery fur winding yarn or thrend on to bobbins

91 F. IL Knovitt, improvements in shutters and blinds for windows

lr» G. Kent ImprovemenU In rotary knife-dean lug and polishing machines

"23 J. Moysey and C. Thome, iroprovemente tn hackling machinery

770 W. Kalnfnrth and W. Halnforth. Jnn.. Improvements in rotary corn screens Tor dressing and separating grain

831 J. Bradbury. J. Bradbury, and J. Koberts, improvements in machinery Tor felting hat bodies

954 W. MacLean. Improvements in printing, lithographing, and itnootraphmg

948 A. Harlnw and J. Taylor, improvemeata In machinery or apparatus to be employed iu preparing cotton or other fibrous Substances for spinning

3451 T. Itelssig, improvements In making a new derivative or phenol, and in producing certain colours therewith upon texfMe fabric* and yarns

34(11 C. H. Hudson, improvements in cots or bedsteads, and guaids to be attached thereto

3403 E. T. Hughes, manufacture of elliptic springs, and in apparatus employed therein.—A communication

3403 A. W. I'ocock, improvements in meters or apparatus for measuring water and other liqu'dM

34*4 W. H. Willis, a new or improved apparatus for registering or Indicating the points of games

3445 R. Aoton and J. Mustard, Improvements in machinery for reeding card'ng engines

3172 W. Spence, improvements In the manufacture of soda crystals

347-i T. O. Green, appliance* *or use in the manufacture of an ides or earthenware ami chlnawara

3480 J. Peirce, improved compound machine for cutting tenons and mortises and sawing wood

3485 G. Hammer, improvements in cork-cutting machine*

3488 A. Mitchell, improvements in caissons or apparatus t» facilitate the hulldlng of bridge piers

3194 P. A. S. Langiois, and L. S. Thomassln. ImprovemenU In the manufacture or sulphuric acid

3495 K. Field, valves for at-'am fire-engine and other pumps

,141*4 W.TjTatham. improvements in machinery for opening tin ft breaking hard waste, rags of cotton, woollen flax, or bilk, aud for scutching aud osrdtng fibrous substances

3658 A. M. Clark, improvements in Jaouunrd apparatus.—A communication

8888 K. Shakespear and G. Illaton. improvements in sewing machines

3805 H. Green, improvements in lubricators

1018 A. H. Brandon, improvements In looms.—A eommunicition

3477 J-T. GrifTin, improvements in preparing, treating, and curing sponge to render it elastic aud suitable for use ass stuffing for hedn.—A communication

3488 r. O. Webb, improvements In t^e manufacture of submarine telegraphic cables

3490.1.0. Wilson, an improved revolving engine and rump

3507 J. Boyd, improvements in machinery fur winding yarn or thread upon conical surfaces

3523 w. >hanks, improvements In machinery for forging shoes Tor iiorBee

3541 J. H. Johnson, improvements in crucibles, melting pf'*9retorts, and furnaces,—A communication

854-J b. Krtwr«rd* improvement* In photo-mechanicftl prinilnn

3548 G. Preston and J. Prestige, improvements in apparatus for regulating the supply of wnter to waterclosets

3508 J, Kallantyne, improvements in the manufacture, of yarns or threads

3585 W. I. Hethertngton, improvements in motlve-po«er eiigtoes specially adapted for propelling «hip«

3015 Yf. E. Newton, improvements in harness for looms.—A communication

5031 B. Mo*s. improvements in kilns or apparatus for the manufacture of malt.—A communication

3035 J. Askew, refrigerator for cooling brewers' and dintillers' wort

8001 J. O. Martin, an Improvement in the manufacture; of finii'gs as a substitute for isinglass

3070S. Hiitler, improvement in the manufacture of lace in twist lace machines

!W A. M.i'iark, improvements In wroden pavements and Iu culi it : the i.locks therefor.-.4 eommnulmMnn

71> . ('hatwood aud J. Sturgeon, imj roemmia In clirect-nclin,-: _ . wer liammers

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iRROR OF SCIENCE AND ART.

FRIDAY, JUNE 17, 1870.

I l

ACCIDENTAL COLOURS. N oar recent articles on "Colour and Colour Blindness, it will be noticed that we have treated merely of objective colours; that is to say, of colours that may be said to have a real existence, arising from the decomposition of whito light, and /-a regard to which the eye is to be considered s imply as a passive instrnment forming the organ omt vision, and is in no way employed in the forrmaäon of the eftect it witnesses. Bat under particular circumstances the eye itself is capable of producing a certain degree of colour which has «o real existence, and is visible to the eye only as long as the circumstances that produce the unreal colour are capable of exerting their effect upon the organ of vision. Tu these colours has been applied the term ¡ubjeetiveox accidental, and their production is owing to a reactionary property that the eye possesses under the influence of light, more or lees vivid, and which converts the organ of vision into an active from a passive state. This reactionary power is well described in a letter from Newton addressed to Locke, in which he derribes 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 imago of the Sun reflected from a mirror, andtben turning his eye,when sufficiently fatigued, 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 iegrees, finally disappeared. "I repeated this act a second and third time. At the third repetition, 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.

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 mce vena. Therefore this experiment makes us acquainted with the fact that the accidental colour ansirn; 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 convinces ni that two distinct phenomena are going

on at the same time, namely, that which produces the birder of the complementary colour around the wafer while it is being examined, while at the same time the eye is во affected as to be capable of producing a phantom colour, after the removal of the wafer. To the first of these two classes of subjective colours has been applied the term simultaneous, to the latter, euccedaneous. We will treat of the latter class first, taking M. Plateau as our guide.

The researches of M. Plateau on this subject have led him to decide that the disappearances of images do not vanish with a gradual and regular decrease of brilliancy, but are accompanied with a succession of disappearances and reappearances. The method of observation employed by M. Plateau was as follows :—While one of his eyes was closed and bandaged, he directed the other with fixed attention for a minute at least at a red paper, cutting off all extraneous light by adapting a blackened tube of about fifty centimetres in length, and three in width, to his uncovered eye. When the eye was sufficiently fatigued, he turned his eye to the ceiling, without removing the tube, and without uncovering the closed eye. On the ceiling, he saw projected a green circle, soon followed by a red circular image of feeble intensity ; this red spectrum was followed by a green, which again gave place to the red, and so on, the red appearing as often as four times, though of course gradually decreasing in brilliancy. Notwithstanding Sir David Brewster's assertion that the manifestation of these phenomena are physically impossible in a perfectly darkened room, the complementary image, and precisely the same appearances, can be produced by closing the eyelids, and pressing the fingers upon them to exclude all light. This fact has required some modification of the hypothesis advanced by Brewster to account for the phenomena, of which we shall say more hereafter.

The experiments of Soherffer 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 complementarles 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, ou which he perceived three squares in juxtaposition, ooloured 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 havo been the colour of thj 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 exception to this rule, which occurs when one of the objective colours is the complementary 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 colonr, if projected on a white ground, and completely black if the eyes bo closed.

Since two accidental colours are capable of combining, it might be expected that an accidental could be blended with a real colour, and this is the case, which shows that accidental colours have all the attributes of real colours, excepting stability. The experiment to show this combination is easily effected by changing the black or white screen which we have hitherto considered to be employed as the material on which the accidental colour is projected for a coloured screen. If, for instance, the accidental red arising from prolonged contemplation of the objective green be thrown on a blue screen, a brilliant violet will be the result But it should be noticed, if the accidental red arising from the same circumstances as detailed in the last experiment, be projected upon a green screen the effect will be simply to produce a neutral grey, of a dark tone, that is to say, in general terms, that when the accidental image is projected ou a screen of the same colour as the objective, the effect is simply one of obscurity. On the »ther hand, when the screen is of the same hue as the accidental, or the complementary of the natural colour, the brilliancy of the phantom colour will be much enhanced, and stand out prominent! v from the neighbouring coloured surface. This will be the case, for example, if the exciting

ibjeot be yellow, and the coloured soreen violjt.. Snch are a few of the properties of succédant vu s subjective colonrs. Before we proceed to mention '.he cause of the phenomena we will add a few of the familiarities pertaining to timultaneous tubjective colonrs.

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 ooloured object. Many experiments prove beyond all doubt the capability of the eye to imagine colours while so occupied, and the simultaneous lam 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 perrormed, and which dispel* all doubt on the subject. Take tu о pieces of paper of about twenty inches square, each of which is colonred 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 t > 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 fraia 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 bine, 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 twe colours are in juxtaposition, of which one is the complementary of the other, since each has the tendency to overspread the surrounding space with its complementary tinge, the brilliancy of each must be enhanced, and the result nm-t be to produce colours of greater purity and brightness. The knowledge of this fact is of great use in a variety of cases. For instance, the employment of red hangings and decorations in apartments is not desirable, since the effect of such a oolour would be to give a greenish tinge to the countenances of the inmates, and destroy the reddish colour which is highly prized in mahogany furniture, giving it the appearance of oak or walnut wood. Judging from optical principles, the head-dress that is best calculated to adorn a fair complexion would be a green hat lined with rose-colour, because the rose-tint is reflected on the countenance, and is further heightened by the complementary of the green overspreading the face. Undoubtedly, our example is a work of supererogation, but it equally well serves our purpoeo of illustration. "¡

If whito be brought into contact with any colour, it is of course slightly tinged with the complementary of that colour, but the colour employed becomes deeper and brighter. The same result follows from the involuntary contrast of black, and any colour, and wb.cn black and white are in juxtaposition, the former become* deeper, and the latter more brilliant than when viewed separately. The. same modifications of colour take place, though less distinctly, when the twe objects are not in contact, the alteration of colour becoming lees as the distance between them becomes greater.

Simultaneous accidental colour manifests itself in another entirely different manner, but not lees interesting, аз 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 witli 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 thevarying shades of the spectrum. Count Kumford 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 meat harmonious tints." Yet this "magic tablean" was produced with the most simple apparatus ; nothing more than two little apertures covered with coloured glass, sufficiently 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 op»que 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 manner:—In a room where the illumination is effected by mean* 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 greeTi.

However difficult it may be to believe that we зге deceived in the colour of these shadows, it is by no means difficult to prove that we really are so. We are indebted to Count Rumford for removing all doubt, that attaches itself to this section of subjective colours, and for tearing away the veil of mystery that surrounded them. He arranged his apparatus as usual, and made quite sure that the phenomena of coloured shadows were duly manifesting their peculiarities, and attractions on the screen ; he then proceeded to examine these shadows through a blackened tube, that cut off all the surrounding light, and left visible the shadow &loiv, and, lo I all the brilliancy anil attraction of the phenomenon had vanished, a colourless and obscure shadow was all that was visible, and the philosopher was convinced of the deception. The explanation of the phenomena of coloured shadows is to be found in a moral, rather than in a physical cause, and the theories that account for subjective colours will fail when applied to coloured shadows, and consequently considerable uncertainty attaches itself to this description of phenomena.

The explanatory theory suggested by Scherffer, and accepted by Sir David Brewster, will, with a slight alteration and addition, be sufficient to explain most of the phenomena that the subject of accidental colours produced. To make this sufficiently clear to oar readers, it will be necessary to refer, oven at the risk of repetition, to some of the well-known properties of colour. It is well known that if а diso of paper be painted with the seven prismatic colours in certain pro

portions, and be swiftly whirled round from the centre point, each colour loses its individuality, and all appears of a uniform light gray tint. If the colours wore perfectly pure, the result would be a white light The diagram shows the proportional the of each sector in order to produce such a result. The arc of the circumference occupied by the Violet tint is 80 (leg., of Iudigo 40 deg., and of Blue GO deg., which occupies onehalf of the disc. On the other half are arranged the other four prismatic colours in the following proportions :—Green, GO deg. ; Yellow, 48 deg.; Orange, 27 deg.; and Bed, 45 deg.

But ¡ion» of these sections be paiuted black, instead of the appropriate tint, the result is not a white light, but is of a colour the complementary of that which has not been allowed to appear. An easy method of determining the colour that arises from the mixture of any of the prismatic colours can be understood from the accompanying diagram, where each sector is supposed to be

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covered with the appropriate tint. Let us suppose that the colour is concentrated in the centre of gravity of each sector, then, if any colour be left out, the resulting light will be that colour which is neareet 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 will fall in the line a. This line falls between the Green (g) and the Yellow (^y), hence the prismatic celours without Violet would combine, and form a greenish yellow tint, in which the green preponderates. If green be left out the centre of gravity would fall between the red and violet, which is the true complementary colour of green. Hence, in all coses, the complementary of any colour can be determined by producing the line that bisects the arch it covers, to the opposite side of the circle, when the point at which it meets the circumference will indicate the complementary colour.

We are now in a position to explain how it is t'.at the contemplation of a coloured object devclopes in the eye a tendency to perceive a phantom object of a complementary colnur, 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 contemplation of a white light the eye is in precisely the same position as in viewing the coloured disc when the red has been omitted, when by the rule given above, the light emitted would be a green tending to blue. This simple theory is sufficient to explain most of the phenomena present in the succedaneous subjective colours, but there are certain peculiarities of which it affords no competent and satisfactory explanation, such as the production of subjective colours in complete darkness, aud the combination of the accidental with the real objective colours. The first objection, as we have seen, was asserted by Sir David Brewster to have arisen from a decided physical impossibility; but M. Plateau, too long employed in these observations to be easily deceived, has stated that he has seen such an effect, and its existence is now so completely recognised by physicists, as to require some modification of Scherffer's theory, for it is manifestly absurd to suppose that the insensibility of tho eye to a certain coloured light should in the absence of all light, produce a complementary oolour. Neither can this theory be held sufficiently to explaiu the irregularity with which the accidental image vanishes, and the occasional reappearance of the natural image. The ingenious theory of M. Plateau seeks to evade none of these difficulties. He begins by remarking that accidental images are due to a physical modification of the organ, since the size of the accidental image is considerably modified by the distance of tu* surface on which it ie projected, from which it is to be inferred that the visual angle is constant, and

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that consequently the ¡mage is increased, aecol ing as we refer it to a greater distance, which in accordance with the fact. "We see no reasoi says he, " why it should be so on the hypo с l^sfl of a moral cause: the image should theo appear ti us of the same magnitude object."

This prefatory remark being adm be necessary to consider the effect pri the retina by the contemplation of a onluuredl ject, both during and after the aution of f coloured rays. It seems most natural to suppôjB that after the organ of vision has been excite,] Ьг coloured light on the withdrawal of the cuae of excitement, the retina should gradually regain itnormal state, which would occasion the persi«ence of the primitive impression, growiug feeble as the impression vanishes, yet without cuiui°in* its nature, till, like the oscillatory motion of I pendulum, it passes through its normal state, ы point of rest, when the reactionary property produces the subjective image, which, when it Ьаг again reached the maximum degree of brightness, gradually tends to reproduce the primitive impression. AU the phenomena that depend upot time, that is to say in which time enters essetially in order to produce the phenomena, are я plained by this ingenious reasoning, and by с analogous reasoning, with reference to space, tk phenomena of the simultaneous subjective colon are explained. "If while the retina is subject to the action of the coloured light, we ex» ta» the parts of the organ which surround the pis» directly excited, we see that the normal state я not found except at a distance more or less considerable from the contour of that space, and thai this normal state is reached in passing through the effects of irradiation, and of the accidental colours of the second (simultaneous) clang.'' if ere, 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 ali the phenomena with whioh we are occupied, and M. Plateau has pointed out "that they are connected with one another in the most natural manner—that they are simple conséquence« 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 toe reasoning of M. Platean is more satisfactory than that of M. Chevreul.

We cannot close this short article without expressing our sorrow and regr>t that the researches of M. Plateau, and of M. Fichner, searcely inferior to him in his enthusiasm, but less happy in his deductions, have been crowned with a commas misfortune. Too enthusiastic in their endeavour] to produce these subjective colours, and analyse the sensations, they have been smitten with blindness. Under proper medical treatment, we believe M. Fichner recovered the use of his eye, »« the illustrious Professor whose name has bees mentioned so many times is thoroughly inapacitated from pursuing those inquiries, whki have shed around his name an immortal lustre

A PRACTICAL TREATISE ON THE

HARMONIUM.*

By Hebmann Smith.

THIRD DIVISION.—CHAPTER IV

Op The Channels Of The Sou.nd-boa!ü>

The masses of air which are enclosed ta а гмре ar« not brought Willi the same ease into every poMtble kind of vibrating motion, but by means of external action each mass of air is enabled only id give taoae particular vibrations which are not opposed to the reaction from within.—Oersted.

TO whatever extent you may be tempted to investigate the nature of the harmonium, you will do well to take the sentence of the groat Scandinavian philosopher as the fitting prelude to a thoughtful survey of the chorocteriatio 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, aud each speaker on his own showing professes to be а judge and couuoisseur. Nothing is more common than the demand fora good oboe stop, a good clario

* The copyright oí this treatise Is reserved by tbe author.

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 harmonium in the disguise of oboe, horn, clarinet, or violeocello. The old ambition is rife as ever. The dream of the alchemists for an universal solvent, the quest of the Eosicrucians 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 energetio 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 tho perfumes of flowers, yet our skill in chemistry is abashed in the 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 Nature's work. The several classes of instruments formi ng the modern orchestra belong to distinct types, and however we may vary these in grade and power, and increase their mechanical excellence, yet we cannot originate a new type, nor afford to banish a single species. The for m of each instrument, the mode of its musical excitation, and the range it can compass, these 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 be a marvellous good likeness, yet it would be dangerous to our self-complacency to place it side by side with the original—or paste diamond lying in the effulgence of the one fair jewel 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, the 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 nnmistakeable a character that we identify it as belonging to B 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 different result. Do you ever consider that the innuenceswhich go to produce that sensible existence m aenal waves which we call "tone " and quality of tone " is as truly a compound of forces acting in definite relation, and si imulating the ear to recognition just as much as the food we taste and discriminate is a combination of chemical constitnents in definite proportions? There is no change 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 chanoe. Natnre in these, and we might as truly say, in all her movements follows the simple plan of taking the P"h of greatest ease. Water tending to its level ■7 Projectile pursuing its flight aod sinking to its rest, the planet tracing its orbit, all are seekinwe 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 influeuces

under which it comes into existence or activity,
for as Locke wisely defines it, "sound is nothing
but motion."

In the making of Oboes, art faithfully abides
by its traditions, and the same holds good in re-
spect of other typical instruments. In making
the channels designed for the several registers of
the harmonium, we unfortunately have not the
same advantage of antiquity and of recognised
models. Our art is as yet immature and un-
defined, and present models are imperfect or but
casually satisfactory. A little reflection will
show the difficulties inherent in our task. We
attempt to imitate an instrument of fixed type
which contains in one tube or pipe a whole
range or compass of notes. In the harmonium
we have a separate instrument for each note, each
channel being virtually an individual pipe with
an independent character and very independent
ways of showing it. In the original, one con-
formation of tube determines the whole series of
notes, each one growing out of the parent stem
in due relation to the others. We, on the con-
trary, have to deal with dozens of distinct cuttings,
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 proportions 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
accurate measurement yet powerful to influence
the resultant quality of tone. Variations in
length of channel, in depth, in width, in length
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
lift of pallet, in depth of keytouch, in covering
and enclosing, in strength and volume of wind,
and modifications of impulse—these and many
others, all more or less determine the character
of tone of every register, and inasmuch as each
one may be considered as a distinct element in
the composition of forces in every given sound,
each variation we could name would count as a
power controlling or disturbing the grouping and
arrangement of the'clustering spheres 'of aerial
waves where of every sound is composed. The
form of the motion, and the complexity of the
undulations constitute the "quality" of the
sound, and whatever has power in least degree
over the combinations of the form will undnbi •
tably exercise an influence in determining the
path of greatest ease, whether it shall be parallel or
divergent from the prefigured course on which our
calculations have been made, Within every pipe
giving utterance tojmusical sound there is a con-
tention of waves for the mastery, or an accordance
of undnlations reciprocating the vibratory im-
pulses of the exciting agent. Thus it is that by
the preponderance of one or other proportion of
pipe and reed we gain distinctive character of
sound. As in chemistry, B very little difference
in elemental proportions fixes the character of
sweet or acid, of condiment or poison, so it is in
musical tones the most minute differences of re-
lation conduce to our pleasure or our pain, and
cause ns\to distinguish the agreeable and the
dissonant.

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 demonstra-
tions of sound ; but at present we need only call
to mind how the shapes of divergent water jets
are formed by the pipes whence they issue, how
the courses of streams in their channels are re-
sultant from combinations of force, how the sur-
faces 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, subjec£to the same laws,
bears its rich tapestries and wondrous tracerieB
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 likenesses 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 tho tone that comes most natural to it, most

easy under the forces that bear upon it—the greatest ease is its nature, because the inanimate has no will, no aspiration. A channel that is connected with a reed gives not its own tone, but the tone resultant from the combination of itself with the reed; the offspring takes after both parents. If the channel is deeper at the pallet than at the reed, the tone will bo very different to that given by a channel that is deeper at the reed end, or ^that arches in'the centre. Even a pipe 8ft. long, if only bowed the mere fraction of an inch more at the centre than at the ends, will give a perceptibly different quality of tone to that which will be produced from a pipe with perfectly parallel sides. A fact of significence if you only consider it.

We have now to study the shapes to be givon to the channels of our stand 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 fall 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 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.)

MECHANICAL MOVEMENTS*

(Continued from page 269.;

T A Q Another form of parallel ruler. The

Jltl«7« arms are jointed in the middle and

connected with an intermediate bar, by which

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 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

151. Stamp. Vertical percussive falls derived from horizontal rotating shaft. The mutilated toothed pinion acts upon the rack to raise the rod until its teeth leave the rack and allow the rod to fall.

1:"2. Another arrangement of the Chinese windlass.

153. A modification of the tilt or trip hammer. The hammer helve is a lever of the first order.

154. A modification of the crank and slotted cross-head. The cross-head contains an endless groove, in which the crankwrist works, and which is formed to produce a uniform velocity of movement of the wrist or reciprocating-rod.

155. The gyroscope or rotaseope, an instrument illustrating the tendency of rotating bodies tn 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 F at 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 same tendency of rotating bodies. This consists of three rings A A1 A* placed one within the 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 continue in the same direction, no matter how the position of the rings may be altered; and the ring Aa which supports it will resist B considerable pressure tending to displace it.

157. What is called the gyroscope governor, for steam engines, Sec, patented by Alban Anderson in 1858. A is a heavy wheel, the axle B Bi of which is made in two pieces connected 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 will cause the outer end of the piece B to rise and fall. The frame H is driven by bevel gearing from the engine, and by that means th<

* Extracted from a compilation by W. H. T. Bnouw. Editor of [he " American Artisan."

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pinion I is carried rjund tie stationary toothed circle G, an i the wheel A is thus made to receive a rapid rotary motion on its axis. When the frame II and wheel A are in motion, the tendency of the wheel Л is to assume a vertical position, bat this tendency is opposed by a spring L. The greater the velocity of the governor, the stronger is the tendency above mentioned, and the more it overeóme« the force of the spring, and vice versa. The piece B is connected with the valve-rod by rods С D, and the spring L is connected with the said rod by levers N and rod P.

158. Traverse of carriage, made variable by foaee according to the variation in diameter where the band acte.

169. 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 bauds to wind upon the spindle alternately in opposite directions, while the heavy disc or 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:

161. Another simple form of clutch for pulleys, consisting of a pin on the lower shaft and a pin on side of pulley. The pulley is moved lengthwise 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.

163. 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 the limited oscillating or alternate circular motion.

(To be continued.)

PARSONS' WHITE BRASS.

AT the conversazione of the Civil Engineers held a íeí nights since, Mr. P. M. Parsons, well known for his labours in the improvement of ordnance, sent samples of his white brass. Ksactly of what this very peculiar alloy consists l«»ye 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 лк-, and has in practice proved very effective. It

differs materially from the generality of alloys known as white metal, being harder, stronger, and sonorous ; it is, in fact, as its name implies, a species of brass, and behaves like it under the tool when bored or turned, and it is susceptible of a very high polish; at the same time it fuses at a lower temperature than ordinary brass, and can be melted in an iron pot or ladle over an ordinary fire. This renders it useful for fitting-up engines and machines where first cost is an object, as it can be run into the plummer-blocks or framing to form the bearings, bushes, sockets, Ms., without the expense of fitting or boring them, or it can be cast in metal moulds, or like ordinary brass or gun-metal, in sand or loam. The white brass has been found by carefully- conducted experiments to surpass in durability all other anti-friction metals against which it has been tested, and to prevent heating of the journals. The durability of the white brass was ascertained several years since by some very carefully 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 10,400 miles, whilst the two brass bearings in the other end lost 21b. 4oz.; that under No. 36, thirdclass, E. C. J. S., the two white metal lost only 2{ against lib. 6oz. whilst running 20,000 miles; and two under No. 35, E. C. J. S., thirdclass, lost only 2Joz. against lib. 12oz. of the brass bearing whilst running 20,000 miles. The bearings during these periods ran perfectly cool, and were lubricated with oil.

MANAGEMENT OF GAS.

AT 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 ordinary coke scrubber, and it was a question whether iron could not be substituted advantageouäly for coke. One fact, however, had recently been awiertained—viz., that purification by scrubbing was not, after all, such a friend to gas managers as they had supposed it to be. The amount of sulphur in the gas varied from day to

day. The gas referees appointed by the Board of Trade had to determine what should be the maximum of sulphur compounds allowable in the gas of those companies under their jurisdiction, and, therefore, their proceedings were of the greatest interest, not only to the public, but also to the gas managers. The referees had not yet issued any public report on the subject; bnt experiments were in process, under the instructions of the referees; which, unquestionably, would throw much light on the point. Among others, a systematic series of experiments was being made to ascertain the efficiency of each separate part of the various purifying processes adopted in gasworks. The Chairman then alluded to a new apparatus devised by the gas referees for the more efficient testing of the gas of the companies for sulphur compounds other than sulphuretted hydrogen, and thought that its adoption should, in j nstice to the gas companies, be properly taken into account by the referees before they fixed 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 resting 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 one. 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.

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