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NATURE 



{Oct. 27, 1881 



During the last_week a body calling itself the Reunion 

 International des Electriciens has been holding meetings 

 in a room granted for the purpose in the Exhibition 

 building. It is understood to be mainl)- composed of 

 persons who felt slighted at not being appointed members 

 of the Congress, and are determined to have a little con- 

 gress of their own ; but their movements have not attracted 

 much public attention. 



As this will be our last article, we will endeavour to 

 supplement our previous accounts by some information 

 on what must be regarded as the most important of all 

 the objects in the E.\hibition, namely, the machines which 

 generate the electricity. Those which have permanent 

 steel magnets are few in number, and the only large ones 

 are the machines of De Meritens. These usually give 

 alternating currents, but can be made to give direct 

 currents by a change in the connections. The principal 

 type contains five Gramme rings mounted on the same 

 axis, each of them surrounded by eight horseshoe steel 

 magnets with their feet inward. The introduction of 

 the Gramme ring is the chief difference between this 

 machine and the old lighthouse machine of Holmes. 

 The great bulk of the machines in the Exhibition are 

 dynamos, in which the whole current produced passes 

 through the coils of the field magnets, and a large pro- 

 portion of them are of the Gramme type, generally with 

 one pair of straight massive field magnets arranged in 

 one line above the ring, with a pair of like poles near 

 together close to the ring, and with another similar pair 

 below of opposite polarity to the first pair. The ring thus 

 revolves between two very strong poles outside it, and 

 massive iron pole pieces are usually employed, so shaped 

 as to embrace a considerable arc of the ring. These are 

 the machines for direct current. In the alternating cur- 

 rent Grammes, the ring is generally broadened out into 

 a hollow cylinder whose length is as great as its diameter. 

 Sometimes this revolves between four external pole pieces 

 attached to electro-magnets, and sometimes it is fixed, 

 •while four broad electro-magnets radiating from the 

 common axis revolve within it. In some examples a 

 separate exciter giving a direct current is mounted on the 

 same stand and on the same axis. 



The three firms of Siemens at Berlin, Paris, and 

 London have a very large and diversified collect. on, partly 

 historical, partly representing the commercial demands of 

 the present day, and partly embodying their latest ideas 

 for future improvement. The prevailing pattern is the 

 well-known Siemens direct acting machine, in which an 

 armature in the form of a cylinder, about three times as 

 long as it is broad, rotates betweei two sets of pole- 

 pieces, one above and the other below, of opposite 

 polarity produced by the action of four straight flat and 

 massive electro-magnets. The coil of the armature is 

 wound, as nearly as the presence of the axle permits, in 

 planes containing the axis, so that the wires cross one 

 another at all angles at the two ends. 



The most remarkable novelty that stru;k us in going 

 over their collection was a machine in which two arma- 

 tures consisting of cylindrical iron cores, each inclosed 

 between four longitudinal segments of copper, revolve 

 within two hoUo.v cylinders of iron, which are the poles 

 of a compooite magnet, so that each armature is sur- 

 rounded by a pole of one name, while opposite polarity 

 is induced in the outer part of the iron core. The lines 

 of force thus radiate from the common axis with complete 

 symmetry, and the longitudinal coppers cut these lines at 

 right angles in every position, so that the electromotive 

 force in each copper remains constant as the armature 

 re\olves. 



A peculiar adaptation of the ordinary Siemens armature 

 has been made by Mr. Edison. The conducting portion 

 of his armature consists of bars and disks. The bars 

 form the outside of the cylinder, and the disks, with mica 

 between for insulation, are built up into two solid masses 



which form the ends. The intervening portion is occu- 

 pied by the core, which consists of a thousand or more 

 very thin disks of iron separated by silk paper. The 

 course of the current is nearly the same as in a Siemens 

 armature, being first along a bar, then across a dis'-;, then 

 back along an opposite bar, then across another disk, and 

 so on. The ends of the b.irs are disposed along two 

 helical curves at the two ends of the cylinder, each helix 

 having two convolutions. The object of having such 

 excessively thin iron plates is to promote rapid demag- 

 netisation and to avoid the formation of induced currents 

 in the iron. This monster machine has only recently 

 arrived, and is not yet ready for action. Its armature (to 

 which, as well as to that of a smaller machine, the above 

 description applies) is about four feet long by two in 

 diameter. It has two straight and very long field magnets, 

 which are actuated by a branch of the main current of the 

 machine. 



A very common pattern of machine for alternating 

 currents, which one sees under various names, has a 

 number of flattish cylindrical coils disposed in circular 

 fashion like the holes of a siren, and revolving in siren 

 fashion between pairs of fixed cylindrical field magnets of 

 more massive appearance, the number of pairs of these 

 fixed magnets being equal to the number of revolving 

 ariiiatures. 



There are also some direct current machines of this 

 construction. They can be distinguished by having a 

 commutator of many segments on which the brushes rub 

 to collect the currents, while the alternating machines give 

 off their currents from two insulated rings which are not 

 divided in any way. 



Last Saturday evening there was a special gala at the 

 Opera House in honour of the Ele :trical Congress, admis- 

 sion being by presentation ticket. In addition to the 

 ordinary operatic performances there was a somewhat 

 stilted poem in celebration of the achievements of electri- 

 city, which was read between two of the pieces by an 

 eminent comedian ; and the whole performance wound 

 up with a grand chorus calling on the earth to light itself 

 up. Preparations had been nude for illuminating the 

 house by electricity, but they were far from complete, 

 and gas was decidedly in the ascendant. The place 

 where the telephonic transmitters are bestowed was easily 

 recognised, there being a wooden screen about ten inches 

 high and six feet long on each side of the prompter's 

 box. 



We stated in a previous letter that a committee of 

 jurors had undertaken some quantitative experiments on 

 the michines and lamps. These are still going on, and 

 will probably be continued till the Exhibition closes. 



The chief practical result of the Congress has been the 

 agreement to adopt the British Association system oi 

 units, and we understand that Prof Everett's book, 

 which is the recognised exposition of this system, will 

 be immediately translated into French, German, and 

 Italian. 



THE IRON AND STEEL INSTITUTE 



ONE of the most interesting feitures connected with 

 the recent meeting of the Iron and Steel Institute 

 was the fact that the Arsenal authorities abandoned at 

 last the official reserve which has so long been com- 

 plained of, and descended into the arena of professional 

 discussion by reading papers on the manufacture of 

 ordnance, projectiles, small arms, and gun-carriages, and 

 submitting them to public criticism. We must specially 

 congratulate Col. Maitland, the present distinguished 

 head of Woolwich Arsenal, on having had the courage to 

 take this step. His paper on the Metallurgy and Manu- 

 facture of Modern British Ordnance was extremely in- 

 teresting. Its production also was well timed, coming at 

 a period when the confidence of the public was consider- 



