kis, p. 317), 18 exemplefied... in the colours exhibited the gravitation of the earth and form a sweep, or of the cutter, stands above the centre of flexure of the bar. Perhaps "D. H. G.," or some one of your able contaibutors, will kindly take the trouble, either to point out where my error lies, or should I by chance be right, to suggest a method by which the defect can be remedied, otherwise than by lengthening the already somewhat long crank, by increasing the thickness of the bar, or by altering the position of the parts in such manner, as will render it difficult to adjust the strap truly to its work?-FOREIGNER, [2633.] RAISING WATER.-Thanks to "Senex for his answer to my question, but his plan does not meet my case. If any brother reader has any knowledge of the rope pump, and would give information of its advantages or disadvantages over the ordinary suction pump for deep wells, he would oblige.-W. S.O subscriber be kind enough to give a brief description [2634]-PAPER-HANGING.-Will any brother of machinery for printing paper-hangings, with their probable cost ?-A. R. K. 260-HYDRAULICAN, [2635] UNNOTICED QUERY. - PUMP FOR MODEL STEAM ENGINE-Will any kind reader please favour me by answering the query (2129) in No. [2636.]-CEMENT FOR JOINING BOARDS.There is a cement in use at present for joining boards together. Could any of your readers say where I could get it, or how to make it? Or is it possible to make glue resist water? If so, by what means ?-ONE IN A FIX. USEFUL AND SCIENTIFIC NOTES. [2022.]-TOF.R.A.S."-May I be allowed to ask a few questions of our learned and ever-obliging F.RAS." 1. How can I, when I know the foci of the constituent lenses of a Huyghenian eye-piece, calculate the power thereof? 2. What does he consider the smallest achromatic refracting aperture with which sive stars of the trapezium O Orionis can be seen? Would he think a 3in. good, that would show them? 3. Some time ago," F.R.A.S." said, that a 24in. would not divorce stars less than 2-5 apart, but according to Dallmeyer's formula (as given last week by the Rev. INTERESTING FACTS, p. 63.-GERMAN MILE T. W. Webb), it should divorce a 6 mag. pair, only-The "Almanach de Gotha," edited at the well-known 192 apart. Does "F.R.A.S." think that it would not geographical Institute of Justus Perthes, gives the foldo this? 4. Are the eye-pieces used in reflecting and lowing reductions:refracting telescopes the same? 5. In viewing a star, 1 kilometer = 0·1347629 geographical miles say a 733in. achromatic, and power 700, would it not 1 geographical mile 7 kilom. 420438 present a disc larger apparently than in a 3in., and power 250? Allow me to congratulate you on your improved appearance and size.-SCORPIO. [2623]-SCIENCE QUESTIONS.-Our Science Department put some examination papers before us last year, which leave, I think, about 9 per cent. of our teachers in the fog. As our ENGLISH MECHANIC does not like to see nor leave, any one in the fog, may I ask the following questions. 1st. In the plane geometry honours paper, show how to construct a triangle A B C, the base A B being 2.5in.. its height 175, and the sum of the sides AC + B C 45. 2nd. In the building construction, the advanced paper contains some ancient specimens, which are very little known at the present time; at least the correct dimensions are not known, nor are our teachers or students in possession of any books which give the requisite knowledge, and therefore I should be much obliged if you inform me whether a student is expected to show his knowledge 1a making a design similar to those given, or is he to show his acquaintance with the structures of which they give sketches. The latter is, I think, impossible, the dimensions given are not sufficient, nor do they correspond with the sketch. For instance, in the sketch of St. Thomas's Church at Charlton (a), in the span of the roof two lines are given, which appear equal on the sketch, but one is said to be 15ft. Sin., and the other 6ft. 9in.-STUDENT IN A FOG. as 1 English mile = 1 kilom. 609315 = 0·216876 geog. mile.-BERNARDIN. BALLOONING.-Mr. Coxwell has commenced his aerial voyages somewhat earlier this than he did last year. Or the 12th inst. he ascended from the Gas Works at Hornsey, and travelled 35 miles in an hour and a half-descending some miles beyond Chelmsford. On the 7th ult. the aeronaut and his pupils made the first ascent of the season from the neighbourhood of Tottenham, the descent taking place four miles north of Bishop Stortford. The famous "Nassau" balloon, built by the late Mr. Green, has during the winter undergone a thorough restoration by its present proprietor, Mr. Coxwell, who purchased it last July This celebrated balloon was made at a cost of £2105, being composed of the best Italian silk, manufactured by Mr. H. Soper, of Spital-square. Mr. Coxwell has recently had a fresh quantity made by the same firm at 18s. a yard, and the "Nassau" balloon will be soon available for further explorations. This was the balloon in which Mr. Green made his remarkable trip to Germany, and also the one employed to take up Cocking's para hute. After its completion it will be inflated for exhibition. The veteran Green, who died recently, had determined, although 85 years of age, to accompany Mr. Coxwell in his first ascent this season, and he declared that the repairs and additions made by Mr. Coxwell would render the "Nassau" as good and safe as ever. He The he had found to be free from those objections. ANSWERS TO CORRESPONDENTS. EDITOR of the ENGLISH MECHANIC, 31, Tavistockstreet, Covent Garden, W.C. All communications should be addressed to the GEO. RYLAND, BIRMINGHAM. On the 1st of April last we considered it writ down in our duty to caution the public against a Mr. Howard Ryland, of Birmingham, by printing the following letter: "Borough of Birmingham Police Office, 1st February, 1870. "SIR-Sergeant Jenns reports that H. Ryland has an office at High-street, Birmingham, but has not been there for six weeks. The last time we heard from him was from Hereford. His letters are called for by his father. There is no doubt but that they are swindlers.-Yours truly, "Mr. "G. GLOSSOP, Chf. Supt., J.A., C.C. As the father of Howard Ryland naturally feels aggrieved at being called a swindler, and as we had no intention whatever of so designating him, we beg to express our sorrow for having accidentally mixed up his name in the caution we gave to the public. We therefore unhesitatingly offer our apologies to him and to the public for any pain we may have given him, or for any injury he may have sustained by our inadvertently linking his name with the statement made by the Birmingham police authorities. We therefore cheerfully withdraw all imputations affecting his character. [2624.]—PROPORTIONS OF SPACE.-Can any brother reader tell me the proportion between the space occupied by any substance solid and when in balls? Or, to vary the question, if 6 cubic feet of lead weigh say 1000lb., what weight of lead shot can be packed in a case of similar dimensions?-MECHANICUS. [2625.]-BIRDS' EGGS.-I have a good collection of birds' eggs. How can I best preserve them, so that they may last as long as possible ?-RUSTIC. [2626-ARCHIMEDES' LEVER.- Some weeks agy I noticed a paragraph in our MECHANIC, describing a machine said to possess the same properties as Archimedes' lever, invented by a working man. Though stated to be very simple in construction, the working, as shown by description, was altogether unintelligible to my dull brain, and I could make nothing of it. Could any of your talented contributors give a short description of the real Archimedes' lever, and what wonders it was supposed to perform; also, if anything else has come to light about this new invention, which took nigh unto 40 years, according to report, to bring to perfection? Is it registered? Aners nearest you, and draw the wet albumen surface ENGLISH MECHANIC MUTUAL IMPROVEMENT drawing would be very acceptable.-Rustic. [2627.)-STEAM AND WATER QUERY.-My boller water is heated by a patent economiser 2800, driven into boiler by a force pump. Now, the steam in boiler is much stronger than in economiser. consequently it forces the water and steam back from the boiler. Can any of your very able correspondents give a panacen for this?-MANCESTRIAN. [2028.-DIMENSIONS OF ENGINE.-Will any of your numerous correspondents kindly set me right? I want a steam engine, 6in. stroke and 4in. bore, to make 100 revolutions a minute with 50lb. pressure. What I want to know is, what size the steam ways ought to be, and what size the exhaust way ought to be; what size the steam pipe and what size the exhaust pipe to work economically and right. be thankful for practical information.-CAM. Shall [2629]-THE QUEKETT CLUB-Will "W. H. G.," who answered a correspondent in reference to the Quekett Microscopical Society, kindly inform me if I can obtain the Quekett Journal regularly in Bristol. where I reside? I take the Microscopic Journal (monthly) now, but should like the Quekett Journal also.-ED. H. JONES. [26301-CANOE STRAKES.-The strakes of a canoe being of pine in. thick, how should they be fastened together? With rivets and washers, copper nails, or brass screws? Are the edges chamfered at all, or left square, and how much lap is necessary? Also, what caulking or composition is used to render the canoe water-tight?-THREE INQUIRERS, (2631)-SPHERICAL FORM OF THE EARTH. Will ny reader answer me the following query? Suppose we have a cistern half a mile long and 2ft. deep filled with water, would the water be affected by SOCIETIES. SOMETHING NEW ON SILVERING PAPER. Canadian Journal of Photography:-"Always ready to lay We find the following in the last number of the before our customers anything new or valuable in photographic manufacture, we should not be doing our duty to them did we not describe a mode of silvering the paper which we have found of very great value; indeed, we have no hesitation in stating that anyone trying the plan will be very much pleased with the result. Provide a board slightly larger than the largest piece of paper you intend silvering; cut pieces of white blotting paper of the size of the board. When about to silver your paper, place the board in a convenient position near the silver bath, with one end elevated to an angle of say 30 degrees. Float your first sheet on the bath, and then place a piece of blotting paper on your board. When the sheet is ready to lift from the silver solution, lift it by the two coragainst the end of the bath; lift the sheet of paper very slowly, and allow it to cling with its wet side Ir will be seen by advertisements on our front page, tight to the end of the tray. This it will easily do if the end of the dish. You will thus wipe off, as it were, in Edinburgh, are called for Friday, the 29th, to conyou are careful to lift the paper perpendicularly over that two meetings, one in Manchester, and the other nearly every drop of the free uitrate from the face of sider the propriety of establishing ENGLISH MECHAthe paper, saving waste. The only precaution necessary at this stage is to lift the paper slowly and straight NIC Mutual Improvement Societies. If anything were up, so that it clings to the inside of the end of the disc. wanted to show the wide-reaching circulation and Now lay your sheet face up on the blotting paper on influence of this publication, it might be seen in this your sloping beard, taking care that the end of the movement. In our opening address, at the commencesheet that came last off the bath is laid on the highest ment of the present volume, we stated that our subend of the board. Prepare a second sheet, and when nearly ready to lift off the bath, cover the sheet first scribers and correspondents were in one sense memprepared, and now partially dry, with another piece bers of a national mutual improvement society; whereof clean blotting paper, and lay the second sheet on top upon Mr. D. W. KEMP, of Leith, and Mr. A. TOLHAUof this, as before. Proceed in like manner with the rest, and when finished put another board on top of all, SEN, of Manchester, simultaneously, without any and allow to dry. The advantages of this mode of concert with each other or communication from us, proceeding are numerous-saving of silver, no messing call meetings, at their own expense, of our subscribers and dropping round, perfect equality of sensitising, in Edinburgh and Manchester, to embody in practice absence of measles, mealiness, spottiness, and all defects inherent to imperfect silvering beautiful, a suggestion made by one of our correspondents brilliant surface when printed, and your paper is is only natural that we should regard with interest always flat. If you try this plan you will find it these initiatory meetings, and at the same time cleaner, surer, simpler and better than any other plan express an ardent hope that they may issue in success. with which we are acquainted." METHOD FOR OBTAINING A CONTINUOUS CURRENT OF AIR OR GAS UNDER PRESSURE, FOR BLOWPIPE AND OTHER PURPOSES. Mr. T. L. Patterson, in a recent paper read before the Glasgow Philosophical Society, explained how a continuous current of air or gas is obtained under ordinary circumstances by the mouth blowpipe or the toot-bellows, and then mentioned the chief objections to those two methods, and proceeded to describe a method which It THE following are the initials, &c., of letters received up to first post, Friday April 22: W. Taylor, J. M. G.. F. King, W. R. B., J. H., J. N., Col. S., Kernan with two rolls of MS., T. Brown, W. Farnwall, G. F. S., J. H. P., J. W. & Co, T. H., Jas. Wigan, T. J. W. B., Ed. Youll, A Middletonian, Anti-Discord, W. B. B., Unlearned Man, J. Linton, Sun-Dial, Young Toxopholite, J. K. P., P. France, R. D., Ignoramus No. 2, Vigie, C. Ward, R. F. D., An Old Subscriber, Fidus Achates, Aghalei, Amator Scientia, A. A. Jones, W. F., E. C. D., Edwardum A., C D. R., W. P., D. H. Thomas, W. P., J. P. S., R. W. H., Expectant, Spring-time, G. R. M., C. C. R., Hugh V. Krolow, S. F.. W. H. B., S. W. & S., J. H. W. B.. A Competitor, Nothing but Leaves, Francis Kingdom, J. H., Thos. Evans, A. Bros., T. C. & Sons, Whitley Partners, Clark & Hunt, John Evans, T.M., T. J. O'C., A Young Tyke, A Reader, T. F. C., J. A. Mayo, The Hermit, W. & B., Rattle-brain, J. Crowe, W. H. C., J. A. M., B W., Col. S., J. P. S., J. B. A., E. M., A Practical Man, E. Wedlake, W. R., J. P. S. KENT.-Can't your friend, being at Reading, inquire about the School of Art there for himself? J. H. CHAMBERS asks us whether the character of a man may be traced in his handwriting. No doubt a man's character is exhibited more or less in everything he says or does, and particularly in the manner in which he speaks or dresses. A fop or a swell may be seen in the way in which he adjusts his hat or twists his moustaches. We never knew a man, for instance, with anything worth having in his head who wore his hat on one side. We don't pretend to decipher J. H. C.'s character in his writing; if we ventured an opinion we should say that he was somewhat pedantic and precise, and that he paid more attention to the manner of saying a thing than to the matter it might contain. R. W. WILSON.-The numbers can be forwarded on receipt of 24 stamps. J. W. P. EDWARDS.-The charge is the same for any number of insertions in the Sixpenny Sale Column. ENNUYE.-There is no such paper. It is, as you observe, to be regretted that the greater number of the weekly journals' give so much space to records of crime. Of course they profess to only give them as intelligence, and not with the direct view of pandering to the low passions of their readers. T. H. S.-See recent back numbers. HENRY ALLEN, OR ROBERT COSSENS.-We did not receive the stamps. A FRIEND TO IMPROVEMENT.-We can give you no information. The English Government are not at present likely to take in hand any invention for the prevention of railway accidents. A SMOKER-Answered recently. RABBIT. Scarcely within the range of a scientific journal. ELECTRO.-Described frequently in back numbers. CONTRIBUTOR.-Yes there has; but don't waste your money on such trash. J. W. PURDUE.-Your questions should be put to a respectable London patent agent, who would answer them properly at a moderate cost. You cannot expect us to do so. Write to some of those who advertise in our columns for one of their handbooks. H. JAMES.-We cannot. CALORIC.-There are such stoves. We noticed and illustrated one a few weeks back. WILFRID HODGSON.-Your idea is old. GEORGE FREEMAN.-We cannot advise you. There are just now too many patentees of velocipedes seeking the assistance of capitalists. A CONSTANT READER, (Thurgoland)-You are unreasonable. B. J. WILLIAMS.-The new newspaper postage regulations do not come into operation this year. Your query can only appear in the Sixpenny Sale Column. W. BARBER.-If you read our answers you would have seen that we did reply to you. Your query can only appear in the Sixpenny Sale Column. GEORGE BATES.-We do not see why you could not have given the information. Your present reply is somewhat of an advertisement. W. AYTON (Sydney, N. S. Wales) has sent us four threepenny pieces for four numbers of the ENGLISH MECHANIC, out of which we have had to pay 6d. W. Ayton is probably not aware that the Post Office has authority to register a letter which "unquestionably contains coin," and to compel the receiver to pay the double fee, in the same way that an unstamped letter is charged double. KAPPA.-Consult your dignity, and discontinue the corre spondence. The insertion of your letter would most likely elicit a vulgar retort. In ability, education, manners, and antecedents, this foeman is altogether unworthy of your steel. Some men-fortunately only a few-prefer notoriety to obscurity, and the one in question would no doubt like to advertise himself in holding a controversy with you. "Science for the Young."-Fourth portion next week. "What Stripes the Sunbeam,' by "F.R.A.S.," next week. J. R. T.-A series of articles on Levelling, which proves the rotundity of the earth, has just appeared in the Building News. 1005 T. Turner, 204, West George-street, Glasgow, bricks or blocks 1066 W. B. Haigh, Oldham, improvements in vertical saw frames 1067 L. W. Thomas, Dover, improvements applicable to fireplaces, stoves, and grates 1068 1. Adams, Boston, Massachusetts, treatment of metal surfaces coated by electro deposition with nickel 1069 J. Kirk, S. Shelmerdine, and C. Froggatt, Stockport, apparatus for felting or "planking" the bodies of hats structures for the preservation of fruits.-A communication 1070 J. H. Johnson, 47, Lincoln's-inn-fields, improvements in 1071 J. Howard, Bedford, improvements in ploughs 1072 M. Henry, 68. Fleet-street, improvements in telegraphic apparatus.-A communication 1073 W. Lake, Southampton-buildings, London, improvements in brakes and starting apparatus for railway carriages. -A communication. 1074 W. R. Lake, Southampton-buildings, improvements in whiffle-trees.-A communication 1075 W. S. Coon. Rochester, New York, applying power to the tools may be adjusted to any desired angle in use. F. R. SMITH." Prie Dieu" wished to know where he could running of machinery and tools, whereby such machinery or get the designs. R. WOODWARD.-Send a letter embodying a description of Titanic steel, and we will insert it. W. H. L. thinks Mr. Proctor "is too hard on poor Mr. Beardsley, and that it would be better if Mr. P. would argue with his opponent instead of abusing him." W. H. L. should remember that Mr. Proctor has recently written an elaborate series of articles on the earth in this publication. MARINE BICYCLE.-G. EDWARDS.-Your drawing is not good enough for the engraver, and your description is not clear. THE SENDER OF THE BRICK-You are mortified at your nonsuccess, and ashamed to state your name. J. B. We do not insert quack advertisements. J. H.-Your reply is purely an advertisement. F. F. C. suggests that Mr. Beardsley should less frequently use the terms "absurd, erroneous, and impossible as applied to theories received by our greatest and wisest of men." D. HITCH.-No stamps enclosed. J. WIGGINTON.-We do not answer by post. A CONSTANT READER says he sent a query which has not been inserted, and he supposes it was because the sender did not write well, or because he could not put F.R.A.S. to his name. Probably the query did not come to hand, or some notice would have been taken of it, however humble the writer might have been. We assure "Constant Reader" that no partiality is shown to correspondents. If a peasant sent to us a suitable query it would be inserted, and if a peer sent us an unsuitable one it would be unceremoniously dropped into the waste basket. J. H. R. The query appeared a fortnight since. 1076 G. A J. Schott, Bradford, manufacture of yarns or threads 1077 B. Baugh and B. Walters, Birmingham, door knobs 1078 E. Lord, Todmorden, cleaning, preparing, and spinning cotton substances 1079 E. Weare, Stonehouse, using the waste threads of condensing carding engines 1080 W, Angus, Fraserburgh, mast-head and other hoisting blocks 1081 M. Bailey. Islington. and W. J. Almond, Cheapside, apparatus for spinning, doubling, and throwing silk, cotton, &c. 1082 C. Joseph, South-place, Kennington-park, improvements in filters.-A communication. 1083 W. Spence. 8, Quality-court, machines for shaping staves for casks and barrels.-A communication. 1084 A. V. Newton, 66, Chancery-lane, improved means for working railroad switches.-A communication, 1085 C. Hamilton, Stratford, improvements in bedsteads, whereby they may be rendered available as an escape in case of fire. 1086 R. Marchant, Torrington-square, perpetual motion 1687 J. Philipson, Newcastle-upon-Tyne, improving the windows of carriages 1088 F. W. Brooksbank, Nottingham, twist lace machines 1089 W. R. Lake, Southampton-buildings. an improved mode of utilising cotton waste.-A communication. 1090.-F. Pattison, Glasgow, a new or improved metalfounder's blacking 1001 T. Dale, Kingston upon-Hull, apparatus for extinguish ing fires jectiles 1092 A. Taylor, Lydbury, improvements in guns and pro1093 W. R. Lake. Southampton-buildings, improvements in looms for weaving.-A cómmunication. 1094 J. Plaskitt, Lincoln's-inn, improvements in velocipedes. -A communication. 1005 L. Stewart, Edinburgh, improvements in wheels 1096 W. Jesty, Gosport, improvements in compositions for coating ships 1097 G. Spencer, 77. Cannon-street, London, patterns on the surface of kamptulicon or other similar substances the construction of engines 1008 W. Simpson and A. Gardner, Ilford, improvements in 1009 R. J. Everett, West Ham, utilising waste products from gasworks 1100 A. V. Newton, 66, Chancery-lane, improvements in the production of metallic alloys of manganese.-A communication 1101 W. R. Lake, Southampton-buildings, improvements in knitting machines 1102 A. A. Wilbaux. Paris, engraving on glass, metals, wood, and other substances 1108 P. N. J. Macabies, Paris, water-feeding apparatus for boilers 1104 W. R. Lake, Southampton-building, drilling or boring rocks. A communication 1105 W. Cotton, Loughborough, improvements in the manafacture of looped or knitted fabrics 1106 C. Beard, Bury St. Edmunds, construction of partitions of walls 1107 E. De La Rue, Cranford, improvements in croquet mallets 1108 E. P. Sheldon, Carlisle, improvements in water meters, and in apparatus for boring cylinders 1109 H. Brooks. 31, Cumberland-market, Regent's-park, receptacles for containing liquids 1110 T. White, Birmingham, covers for dishes and plates 1111 1. Baggs, High Holborn, improvements in making white lead 1112 T. Dickins, Middleton, machinery for spinning, twisting, doubling, and throwing silk 1113 A. Borgnet, Swansea, construction of retorts, muffles, pots, and furnaces 1114 H. E. Newton, 66, Chancery-lane, apparatus to he employed in the performance of gymnastic exercises.-A communication 1115 J. Craven, Wakefield, apparatus for raising and lowering heavy bodies 1116 T. Wood, Manchester, omnibuses and apparatus for indicating the number of passengers entering therein 1117 N. Murphy, Norwood, Ireland, securing more effectually the duty upon spirits in distilleries 1118 A. L. Dowie, Glasgow, improvements in treating copper, zinc, tin, and their compounds 1119 P. J. X. Gunthe and J. A. C De Latouche, Paris, revolvers 1120 J. L. Norton, Belle Sauvage Yard, Ludgate-hill, dressing and farrowing millstones 1121 W. H. Delamare, Deptford, machinery for treating cotton seeds 1122 J. Barrow, West Gorton, treatment of napthalene, and of hydrocarbon bodies containing napthalene. 1123 P. Toepler, Gracechurch-street, cleaning wool 1124 J. Townsend, Glasgow, applying heat in various chemica operations 1125 A. M. Strathern, Coatbridge, and D. G. Morrison, Glasgow safety apparatus for steam boilers 1126 W. F. Murray and T. D. McFarlane, Glasgow, apparatus for shaping plastic materials 1127 T. McIsaac, Putnev, folding bed table 1128 W. Spence, 8, Quality-court, Chancery-lane, manufacture of hats 1129 G. C. Cooke, Woodford, apparatus for scoring or recording numbers All persons having an interest in opposing any one of such applications are at liberty to leave particulars in writing of their objections to such application at the office of the Commissioners before the 11th of April, 1870. PATENTS SEALED. 3024 J. Raper, improvements in looms for weaving 5031 J. Bottomley and W. Bottomley, fulling or milling woollen and other woven or felted fabrics 3037 M. Ker, improvements in curtains 3041 W. Lake, improved nut for screw bolts 3044 A. Forder, velocipedes 5047 A. Clegg, improvements in sewing machines 3049 F. R. Window, producing photographs in pigments 3053 A. Munro, cutlery, edge tools, agricultural and other implements 8055 B. Sulman, stamping and canceling press 3058 A. Brady, improvements in purifying iron or any other metal.-A communication 3064 H. Brooks, metallic cap or cover to glass or other bottles or vessels 3065 J. Becker, apparatus for stopping bottles 3067 W. R. Lake, improvements in rotary blowing engines.A communication 3091 P. Walker, apparatus for rendering coal mines less injurious $115 O. L. Hopson, apparatus for reducing the diameter of wire or rods for wire drawing 3150 C. Sacré, improvements in the manufacture of wrought iron 3200 C. De Ville Wells, improvements for regulating the speed of marine steam engines 3256 W. Harris, locks and latches 3322 J. Woodward, liquid meters 3509 J. F. Kent, mortising, tenoning, and sawing machine 3593 P. Koch, manufacturing untapped nuts intended for screw bolts 1011 E. Pilling, looms for weaving 1013 J. Petrie, washing wools and other fibrous materials 1015 J. M. Kilner, apparatus for laying submarine telegraph cables 3056 W. Heywood, improvements in carriages 3066 G. M. Ashforth, applying motive power applicable to working sewing machines 3073 R. J. Goodbody and R. E. Donovan, apparatus for roasting tobacco for snuff 3074 T. Gibb and C. Gelstharp, furnaces for calcining ores 3076 J. R. Grayson, apparatus for clipping or shearing horses 3084 R. Scott and W. McIvor, sulphuric acid residues utilised and employed for the production of sulphate of soda 3087 T. Hydes, J. Bennett, and J. E. Bennett, propelling ships 3101 T. Hoey, improvements in fire places $102 D. Spill, preparation and use of solvents of xyloidine 3108 T. Dunn, improvements in locomotive steam engines. 8123 J. Watson, improvements in presses for compressing cotton 3135 A. Knowles, apparatus for cutting and getting coal', 8145 J. H. Spencer, compound for lubricating the journals or necks and bearings of roils, rotating shafts, and other rotating bodies 3189 N. W. Blanchard, substitute for curled hair for upholstering and other purposes 3199 S. Busk, shoes for horses and other animals.-A communication 3249 L. Nasch, button-hole sewing machines 3287 P. Koch, fastening the knobs or handles of locks.-A. communication 3505 C. Ashbury, improvements in steam boilers 3315 T. Weston and H. Weston, manufacture and coating or casing of metallic tubes and rods 8682 G. T. Livesey, apparatus used in the manufacture of gas 3717 J. B. Gough, improved collar stud 14 J. Smith, sickies and wires connected with mules for nning 208 D. Robertson, improvements in carding engines 358 J. Ward and J. Bowing, preparing and drying yeast 350 H. Bond and J. Kiley, manufacture of quilts, counterpanes, and table or toilet covers 483 S. W. Clark and W. K. Sykes, signal and other lamps 545 S. Hulme, removing paint from wood 512 W. B. Adams, railways, tramways, common roads, and machines and vehicles to run thereon 578 A. Godillot, an improved military tent. 509 L. Sterne, construction of wheel tires The English Mechanic AND MIRROR OF SCIENCE AND ART. FRIDAY, MAY 6, 1870. WHAT STRIPES THE SUNBEAM. BY A FELLOW OF THE ROYAL ASTRONOMICAL HERE are, probably, very few modern discove THER ries which have excited such widely-spread interest as that of what has been called Spectrum Analysis; in fact, it is almost impossible to peruse, even in a desultory way, much of the current Scientific literature of the day without meeting with references, more or less explicit, to it. Inasmuch, however, as the subject has not hitherto been treated formally in our columns, and inasmuch, further, as it appears to us that a familiar exposition of it may enable many of our readers to appreciate and understand the references to which we have alluded, and which, presumably, have now little or no meaning for them; we have determined to endeavour to place the whole matter in as popular a form as it is susceptible of explanation in, and to tell the marvellous tale of the detection of the chemical constitution of our great centre of life heat and light, the Sun (and even of that of some of those infinitely distant bodies which spangle the midnight sky), by the aid of a mere triangular stalk of glass and a narrow slit in a metal plate. We must, however, ask here, as we did on a former occasion, for the sustained attention of the reader. It is not a very easy subject which we have taken upon ourselves to discuss, and in our attempt to make it apprehensible we shall have to proceed, step by step, with, it may be, more or less iteration, in a predetermined sequence of explanation. We would, then, request the Student, on no account to proceed with any paragraph, after the first, until he has thoroughly mastered the preceding one. If he will try his best to comprehend us, we will promise to use all our endeavours to be comprehensible; and to use only such language, and employ only such illustrations, as shall be within the grasp of any moderately-educated artificer who may be sufficiently interested in the subject to follow us. prism, therefore, being placed in this posture, I first proposition, that lights which differ in colour dicated is at once so important and so striking It was in the year 1675 that one of the greatest, if not the very greatest, of Englishmen who ever lived, Sir Isaac Newton, made the remarkable discovery that white light was not homogeneous; that is to say, that it could be split, or decomposed, into lights of various colours, and this he ascertained from the circumstance that when, under certain conditions, a ray of white light is refracted or bent, its components are bent in different proportions, or some more than others. He demonstrates this in Prop. 1., Theor. 1., of his "Opticks," published in the year just mentioned, under the heading, "Lights which differ in colour, differ also in degrees of refrangibility." Into his proof of this we need not enter, since we are now more immediately concerned with his second proposition, "The light of the Sun consists of rays We may add to what we have said, that, by redifferently refrangible." The annexed figure(Fig. 1) copied from the "Opticks," will serve to exhibit ceiving the spectrum as described above, upon a the manner in which he shows the truth of this screen, and then cutting a slit in that screen so as to let light all of one colour, say green, pass through experimentally. Through a round hole F, of in an isolated state, Newton found that such Ard of an inch in diameter, Newton allowed the colour was no further decomposable, and that, on Sun to shine upon one face B C, of a triangular letting this ray fall upon a second prism, he only stalk of glass (which we call a prism), "whereby," got green light upon another screen placed behind as he says, "the beam of the Sun's light which the first to receive it. He further showed that by came in at that hole might be refracted upwards examining the spectrum P T through a second towards the opposite wall of the chamber, and there form a coloured image of the Sun. The axis of the prism (that is the line passing through the middle of the prism from one end of it to the How or why this combination of colours affects other end, parallel to the edge of the refracting the eye as white light, is too recondite a question angle) was in this and the following experiments to be discussed here, even were there any tenable perpendicular to the incident rays." This means theory to account for it. It is mainly connected nothing more than that a sharp edge of the prism with the anatomy and physiology of the eye itself, was downwards, and that such edge was parallel and it is therefore impossible, in this place, to do to the shutter in which the hole was made, and more than refer to it. We may just say, though, to the floor of the room in which the experiment that the phenomenon itself may be exhibited in was tried. Having found the position of minimum another form by means of a rapidly-rotating disc deviation of the prism (ENGLISH MECHANIC, upon which the prismatic colours are painted in Vol. X., p. 629), he proceeds as follows:-"The thi: due proportion, and by the motion of which prism placed below the level of the first, so as to E they are blended, so that the disc affects the ey e the superposition of blue and yellow, and that it that the green, for example, is not made up by So far as we have gone, then, we have arrived at this result, that what we call white light is in yellow, orange, and red lights, and that, after reality a mixture of violet, indigo, blue, green, falling upon one face of a prism, a beam of Suninto a sheaf or fan of these its component colours, light emerges from the adjacent face, spread out the blue less still, and so on to the red, which the violet being the most bent, the indigo less, is bent the least of all. We have further learned that each of these is legitimately a primary colour; that is to say, it is of a fixed and unalterable refrangibility in the same medium, and it is monochromatic, or whole-coloured, and, consequently, undecomposable into any simpler elements. Should the reader, however, follow our advice, and repeat Newton's experiment for himself, he will observe that the colours are not sharply defined at their junction with the adjacent ones, but that they melt, as it were, into each other, and that the spectrum is, in fact, a continuous one, without break or interruption. It will readily be seen that this is referable, inter alia, to the shape of the orifice through which the beam of sunlight is admitted, as it is pretty evident that the rays which come through are inclined to each other at the angle (about half a degree) subtended by the Sun's dise to the eye. How the use of a round hole in his shutter caused Newton just to miss a discovery of the most vital importance we shall now very soon proceed to exhibit. Before doing so, however, it will be as well, at this stage, to glance at the physical properties of the variously-coloured constituents of the spectrum, remembering that all light is due to the undulations of a medium pervading the whole of space, the difference in the rapidity of the vibra tions of this medium affecting the eye as differences of colour. Numerical details on this subject may be found in a letter at p. 35 . th. p:.s.Lt volume. With regard to the worls, "extremred" and "extreme violet," with which the table (1. e.) commences and concludes, we may just observe that, beyond the confines of the ordinarily visible spectrum, exist rays of light both more and less refrangible than any of those which we commonly see; but that by certain artifices or contrivances these may be rendered perceptible. Commencing at the red end, we find that the greater part of the heating effects of the Sun's light are referable to these red rays, and delicate experiments have shown that the maximum heating power resides at a point beyond that at which red light, or any light, ceases to be visible to the eye. Sir William Herschel was the first to draw attention to the fact that heating power mainly resided at the red end of the spectrum, announcing his discovery at the very beginning of the present century; while as early as 1777, Scheele published the results of some experiments, which showed that chloride of silver blackened much more rapidly in the violet rays than in any other part of the spectrum. The preponderance of illumi nating power in the yellow rays must have struck every one who ever viewed dispersed light at all. Summing up, then, we may say that the greatest heat resides in that part of the spectrum just outside of the visible red; the most energetic chemical power just within the visible limits of the violet, and the brightest light about the middle of the yellow. But it is time to return to what we were saying as to the shape of the aperture through which the Sunbeam is admitted to fall upon the prism; and we may now proceed to see how Wollaston made (without knowing it) a discovery of very high importance in connection with the subject which we are now considering. Instead of emploving, like Newton, a round hole in his window-shutter, through which a number of overlapping spectra find their way, he let the Sun's light pass through a narrow slit parallel to the refracting edge of the prism, and upon now examining the spectrum he found it no longer continuous, but crossed in several places with fixed dark lines, which were permanent. Wollaston, however, like many other discoverers, seems to have quite failed to see the importance of what he had found out, and the matter slumbered until the year 1814, when the great German optician, Fraunhöfer, took the mattor up, and, by viewing the spectrum of a very narrow slit through a telescope, succeeded in believe, nearly 580 of these lines. mapping, we ceciled " Fraunhofer's lines, even to this day. He further found out that these lines existed in both direct and reflected sunlight; that moonlight and the light of Venus also showed them, and that in the spectrum obtained from each of these sources, the position of the visible dark lines was fixed and invariable. Fraunhofer made another discovery, too, of very great importance, which was that the fixed stars (which it is well known are themselves Suns) gave spectra containing dark lines, but they were not the same dark lines as he had previously detected in the Sun's light, whether directly or indirectly derived from him. incandescent gas, what sort of light will that emit? spectrum of potassium, what a wonderful contrast Prior to entering into any detail as to the kinds of spectra which we obtain when we regard the incandescent vapours of the various bodies to which we have been alluding, it seems essential here that we should make some reference to the method in which these spectra may be observed, and we therefore, to render this more intelligible, here (Figs. 2 and 3) give a figure of one of the simplest forms of spectroscope, the pattern being one of those of that very able and eminent optician, and well-known amateur observer, Mr. John Browning, F.R.A.S., to whom, probably, this instrument owes more than to any one artist living. It consists, in effect, of a very dense flint glass prism P, standing in a truly perpendicular position in the centre of the circle C, which is itself supported by the stand S. The circle C is gradnuted, and upon it is an upright ring F, fixed firmly, another ring M, attached to an index I (reading by means of a vernier V), moves round the circle C on such index. Into this latter or moveable ring a telescope, M T, of the ordinary construction, is screwed. Into the fixed ring is fastened another telescope, with its object glass also directed towards the prism, but, in place of an eye-piece, carrying in its focus an arrangement of "knife-edges," shown in front view of Fig. 3. This consists of two thin plates of metal s s', with their inner edges carefully ground and accurately parallel, and these are made to approach to or recede from one another by means of the screw For the better explanation of our subject, we with a milled head a, the effect of this being to will now dismiss temporarily from our considera- make an exceedingly clean sharp slit of any width tion the spectra of the celestial bodies, and contine that may be required; a part of this slit is covered ourselves for the present to the effect of heat on by the reflecting prism p, by means of which the terrestrial ones, in so far as such heat leads light from any source placed in the position of to the evolution of light. Every blacksmith knows the candle C, is reflected through it, together that when an iron rod is put into the fire it first with that passing directly between its jaws; so arrives at a red heat, and as it becomes hotter it that the spectra, side by side, can be seen in the gradually emits light of greater and greater re-field at the same time, and the comparison instifrangibility, until ultimately it ends by giving off tuted between them. It is only needful to say at rays of all degrees of refrangibility, or becomes, this stage that the slit formed by the knife-edges as they say, white hot. If the reader will watch i sturnedtowards the light whose spectrum is to be the gradual heating of a common poker by the examined; that of course the rays pass out of the aid of one of the prisms which we have recom- object glass F parallel, fall upon one face of the mended him to procure, he will find that it will prism P, are refracted and dispersed by it, and begin by the emission of red rays; that as the that then they enter the object-glass M, and the heat increases, its spectrum will lengthen; and spectrum is observed through the telescope TM, that orange, yellow, green, blue, indigo, and violet to which the object-glass belongs. light will in succession become visible, the whole Let us conceive, then, that, this instrument of the prismatic colours becoming apparent when being in adjustment, we turn the slit towards the poker is intensely white hot. The same a burning spirit-lamp, into the flame of which we sequence of phenomena will be exhibited by any will commence by imagining that sodium, siy in body, solid or liquid, which can be sufficiently the form of common salt, has been introduced: heated; and it is most important to remark, that and let us proceed to see what sort of a spectrum in each and every case (with the solitary and un- this yields. Certainly a most remarkable one; important exception of an extremely rare substance called Erbia which we may quite neglect here) the spectra of all incandescent solids and liquids whatever, are continuous-that is to say; uninterrupted and uncrossed by dark lines of any sort or description. But suppose that, instead of a solid or liquid body, we are dealing with an a brilliant yellow band, and that is all. The light 1 ths of 180000000 grain of soda has sufficed to show the sodium spectrum, and to flash up in the instrument as a brilliant yellow streak!!!; and further, although it is of little importance to our present object, that this line of sodium, when examined with adequate, optical aid (of which more by-and-bye), is seen really to consist of two lines, like hairs, close together. We may perhaps also add, that we inay have as many substances in a vaporous form as we please at the same time in one lime, and that as they successively become volatilised, their spectra will appear one after another when that flime is examined by the aid of the spectroscope, ultimately remaining simultaneously visible until the dissipation of the respective substances which produce them. (To be continued.) ELECTRICITY-ITS THEORY, SOURCES BY J. T. SPRAGUE.* Templer forms of, is the combination o HE simplest form of galvanic generator, and alternate plates of copper and zinc; most electrical works employ a good deal of space, and many figures, in describing the various forms devised by way of improvement, by Cruikshank, Wollaston, and others, consisting chiefly of the mode of arrangement in the containing vessels, the use of double copper-plates surrounding the zine, and such-like matters, the value of which But as the simple copper-zinc arrangement is the has been entirely destroyed by further progress. most unsatisfactory form known, it is simply tions of it, and therefore I shall only refer to it wasting time and space to describe such modifica when required for elucidating principles, and as the starting point of all the forms. 109. EXCITING SOLUTIONS.-A current may be generated by two metals in many solutions, but for the single liquid cell the only practical re-agent is sulphuric acid. This is the most powerful, and the cheapest, as it may be bought as commercial oil of vitriol, from about five farthings a pound, and still lower in large quantities. I may as well say here that for the convenience and information of readers I shall thus name the price of all the articles employed; those prices will be those I pay myself, knowing where to go, and are ordinary fair retail, not wholesale or in small quantities, and particularly buyers at trade prices; at the same time, ordinary purchasers chemists, as the retail dealers in drugs are called, will be asked much more. Ordinary rectified oil of vitriol of full strength, specific gravity about 1840, will serve, but ordinary brown vitriol should be avoided for two injurious to the silver in a Smee's cell, and cause reasons; if it contains nitrous acid it would be local action on the zin, in spite of amalgamation, in all; to test for this, mix a few drops with water in a test tube, and drop in a crystal of pure ferrous sulphate, or green vitriol, of er the scil has cooled; if a brown colouration is produced, reject the acid. Another very common impurity is arsenic, which would be given off with the hydrogen and form a most deadly poison, if much is breathed, and be unwholesome in any case. Sulphuretted hydrogen passed into the diluted acid will cause a yellow precipitate if there is arsenic present. These are the only impurities of any consequence. Lead gave a momentary deflection of 39°, which fell in a few minutes to 5. 112. SILVER AND ZINC. The silver in this case was better than rolled metal, as it was deposited on electrotype copper, thus giving a favourable surface; this answers perfectly well. If a thick plate is laid on, it gives of course a higher conducting power, and is cheaper, for even the two coatings will contain less silver than a silver sheet of such thickness as to bear practical treatment. It gave 50° falling to 48, 47, 46, 45, at five minute intervals, and 43° after one hour. Like copper, the surface is covered with a brown film, due to the condensation of hydrogen. A good solution is made by mixing 1 part by bulk with 10 of water, which should be soft, as water containing lime is apt to form a deposit on the metal surfaces; if no other is accessible, it should be boiled with a little carbonate of soda and allowed to cool and settle before nse; 100 grains by measure of such a solution will dissolve about 11 grains of commercial zinc, but it is bad economy to nearly saturate the acid, particularly 113. PLATINISED SILVER.-Smee having asif several cells are combined in series, as zinc is sured himself that the nature of the surface was then pretty sure to be deposited on the lower of the greatest importance, and that the hydrogen part of the negative plate, which is thus destroyed is more readily given off from a rough surface for the time, and from which, as the zine is pure, than a smooth one, and also bearing in mind it is a troublesome process to dissolve it again. that platinum has the highest electro motive But allowing for impurity in zine, local action, force of all the metals as opposed to zinc, deand a due proportion, or about one-fifth of free posited this metal as a fine black powder on the acid left, one pint of this solution would dissolve surface of silver, thus attaining both those obabout 1 oz. of zinc. We may thus calculate jects, and yet avoiding the expense of platinum, the work any cell is capable of doing as about and also the low conductivity of this metal, and equal for each pint of solution to 24 equivalents the battery thus arranged, and which justly bears of chemical action, this being the true electrical his name, is one of the most valuable gifts ever unit of "quantity," as I shall hereafter explain. made to electrical science. It is of simple conThe cost of generation for each unit would thus struction, the silver sheet is held in a wooden be that of one pint of solution, 13oz. of zinc, frame in a saw-cut down the middle of the inside and a fair per centage for wear of negative plate surfaces; the top and bottom bars may be in. and vessels, divided by 24. This is the acid, and thick, and the sides, the wood being these the conditions applicable to all the follow-well baked and soaked in melted paraffin before ing forms of simple cell. putting together by the usual mortises and tenons, and afterwards well covered with shellae varnish; a sheet of zinc is held on each face by means of a brass clamp with a screw, which presses them against the frame, and carries also the binding screw for the connection, that for the silver passing through a hole in the top bar, and being soldered to the silver; the zincs should be narrower than the silver, in order to give free escape for the gas. 110. COPPER AND ZINC.-When first a pair of plates are immersed in dilute sulphuric acid, and the wires connected to a galvanometer, a considerable deflection is produced, marking a powerful current, but even in a few minutes the effect rapidly decreases. The following experiment was made for purposes of comparison, with plates 2in. by lin., half an inch apart, in the above-described solution, the plates perfectly fresh, the copper having been washed in nitric acid, and then in several waters; the deflections are those of a Tangent Galvanometer, and therefore capable of comparison, and, as will be hereafter explained, of actual valuation. First deflection, 40°, after successive intervals of five minutes, 34, 33, 32, 31, 31, 30, after one hour, 28, and after an hour and half, 26. The galvanometer and connections consist of about 15ft. of No 13 copper wire, a resistance by actual measurement of 031, or 1-32nd of a British unit. After a short while the copper is seen to be covered by a dark film, which it is commonly stated is oxide of copper, and the other metals contained in it. This is erroneous however, for it is evident that oxides could not possibly form in the presence of nascent hydrogen; it is really a combination of this hydrogen with the metal, and the diminishing power of the cell is due to the formation of this bydride or alloy, which prevents contact of the copper with the liquid, thereby increasing the internal resistance, while the affinity of the hydrogen in this condensed condition for the acid radical resists the polarising power of the zinc, and therefore diminishes the electromotive force of the couple or cell. Silver ready platinised may be bought, but it will require occasional renewal, and the process is very simple. The silver, being perfectly clean (it is best to wash it with nitric acid), is placed in a cell containing acid solution, and connected to it is a wire with a small piece of zinc attached, this may be merely wrapped in a piece of blotting paper, or a porous cell may be used to keep it out of reach of the platinum. The zinc is now dipped into the acid to a small extent, in. square is enough, so as to produce a very slight action, and then a drop or two of platinic chloride is added to the acid, and immediately it begins to be reduced on the silver; after this is found to be wholly coloured, the action may be increased, and more platinic solution added, and at the last a brisk action should be produced, the object being, first to secure an adhesive deposit, and then a pulverulent one of platinum. The platinum solution is made by dissolving scraps of the metal in aqua regia, or a mixture of nitric and hydrochloric acid, by the aid of heat. Crystals may be obtained by evaporating to dryness and re-dissolving, but for the purpose required this is needless, as the excess of acid is not injurious. Pure copper, as deposited by the electrotype Treating thus the plate used in the last experiprocess, has a higher electro-motive power, pro-ment, and using with it one zinc, so as to have the bably because of its purity, but also on account of same conditions as in all the other trials, it gave the nature of its surface, which is covered with 71°; at 5 minute intervals, 66, 63, 61, 59, 57, in innumerable fine points, from which the hydrogen is given off more readily than from a smooth surface. Hence if a copper negative plate is to be used, it should have a deposit of copper formed on it. Such a plate gave the following comparative results-First deflection, 50°, and in successive five minutes, 35, 34, 34, in one hour, 33, and one and a half, 32. It will be noticed that the greatest loss of power is in the first few minutes; indeed, the first de flection is of scarcely any value for the fall is so rapid that it is nearly impossible to say what the true deflection is, or when the needle has reached its position of rest after the first oscillations. an hour, 50, and in an hour and half, 46. Like all the others its power suffers a rapid decrease, in this case due, chiefly, to the remarkable power possessed by spongy or pulverulent platinum, of condensing gases to many times its own volume, and retaining them in this condition. However, these comparative tests, though valuable and instructive, only treat one aspect of the question of value, that of constancy, and relative activity on short circuit; before coming to a conclusion, the action has also to be considered, when varying resistances, such as are met in practice, have to be overcome. 114. I have long been in the habit of using a 111. IRON AND ZINC.-Iron has often been peculiar plate in my Smee's, one composed of recommended as a positive element because its copper wire gauze, 40 meshes to the inch, which surface keeps clean; its value will be evident I first copper by electrotype, and then silver and from the following results, 25° falling to 18 and platanise; the reason I used it at first was to en16 in ten minutes. Still its cheapness may temptable the zinc to be placed in the middle, and to some to use it, a very unwise economy. For this give a freer escape for the gas, and although reason it should be stated that wrought or rolled the surface is at first view diminished by the iron is alone fit for use, as the presence of carbon openings, it is not so really, as the whole of the in cast iron sets up local actions. One reason surface of the wires is active, the back as much why iron is unsuitable is its low conducting as the front. Such a plate prepared for compari power, which adds to the internal resistance. son gave 69°, falling to 50, 47, 45, 44, and in an hour and half, 42; this is less than the solid plate, but the reason is that it was not plated sufficiently thickly, and consequently its surface was smaller than it should have been. As 115. CARBON AND ZINC.-Mr. Walker suggested the use of graphite plates, and has used them in batteries for telegraphic purposes; this combination gave 25°, falling in an hour to 23, and in an hour and a half to 21. It thus appears that the force is lower than with silver, or even copper, probably on account of the lower conducting power of carbon, but, on the other hand, it has the merit of comparative constancy. It has also been platinised in the same manner as silver, which greatly increases its powers. an illustration of the great resistance produced by the hydrogen, I arranged the plate, during platinisation, in connection with the galvanometer, showing a current of 6; the moment the platinum salt was added, and the hydrogen employed in reducing it, the deflection rose to 34°, falling again to 12 as gas began to be again given off. When arranged as in the other cases, it gave 68°, falling to 63, 59, 55, 51, 49, to 37 in one hour, and 31 in an hour and half. SALINE SOLUTIONS.-As it is well to know what attempts fail, as well as what is successful, I may say that many saline solutions will generate currents, but none are of any use in single fluid cells. Thus, carbon and zinc in common salt, chloride of ammonium, nitrate of soda, and various others gave a deflection of6°, rapidly falling below the power of the Tangent Galvanometer; in fact, the zinc is not able to displace the alkaline or earthy metals which are chemically employed to precipitate it. These solutions have important uses in double fluid batteries, but then other affinities come into play, and these salts act chiefly as conductors, and act on the zinc only by being themselves acted on by the other agents, as well as the zinc. 117. Having examined the principal elements employed in batteries which set the hydrogen free, their construction is a matter which need not occupy much attention, for the plan described for the Smee is applicable to all, but without requiring a complete frame; the old fashion of cementing plates into troughs is entirely abandoned, because it is impossible to clean them, a process constantly required, as the copper, when used, needs to be frequently heated to redness to renew its surface, and the zines ought to be well brushed and freshly touched with mercury after 24 hours' full action, or they lose power, and become subject to excessive local action; but if this care be taken the local action is very small, and it is hardly necessary to remove the plates when not in use, unless a long interval is likely to elapse before they are to be used again, as they keep in much better order in the acid. Various experiments have resulted in a loss of from a quarter to half a grain per square inch of surface in 24 hours, in solutions of fall strength. 118. Before passing, however, to the compound forms, I will make a present to the readers of the ENGLISH MECHANIC of a cell of my own arrangement, based on the long series of experiments I have made, and of which the foregoing are a selection. I should have deferred its description till after the examination of the general principles, but so many inquiries have been made lately on this subject that I expect the description will be welcome. The containing vessel is an ordinary stone jar about 5in, wide by 9in. deep; a strip of gauze 15in. by 5in. is treated as before described, but a copper plate silvered, or sheet silver would do, though I believe not so well; this is made into a cylinder fitting inside the jar, and slung by three copper bands or wires (soldered to it and covered with cement or gutta percha after completion) so as to leave a space of 3in. in the jar below it; the suspending wires are turned over to the outside and soldered to a band going round the jar and fitted with a binding screw, a wooden cover is fitted with a hole in the middle, through which passes the connection to the zinc. The zinc is a strip 2in. wide by fin. thick, and at its foot is secured a little shoe or saucer of gutta percha containing mercury, which maintains the amalga mation. Of course the negative element is somewhat expensive at first start, but the object is to give it as large surface as possible; a series of carbon plates might be substituted, but they would cost as much as the silver and have no residuary value, and give less force; the platinising is done at the first charging, taking care to reduce all the platinum before inserting the proper zine. This battery is nearly constant, it deflected my |