Scientific American Supplement, No. 315, January 14, 1882
SCIENTIFIC AMERICAN SUPPLEMENT NO. 315
NEW YORK, JANUARY 14, 1882
Scientific American Supplement. Vol. XIII., No. 315.
Scientific American established 1845
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In admiring the recent developments of electric science as evidencedby the number of important inventions which have during the past fewyears been given to the world, especially in those branches of appliedscience which deal more particularly with the generation ofelectricity and the production of the electric light, there is oftentoo great a tendency to forget, or, at least, to pass over incomparative silence the claims which the great pioneer workers anddiscoverers undoubtedly have to a large share of the merit of thisscientific development.
It is, of course, obviously impossible in anything approaching aretrospect of the science of magneto-electric induction or itsapplication to illumination to pass slightly over the names ofOersted, of AmpŤre, of Davy, and of Faraday, but, in other respects,their work is too often lost sight of in the splendid moderndevelopments of their discoveries. Again, there is another group ofdiscoverer-inventors who occupy an intermediate position between theabstract discoverers above named and the inventors and adapters ofstill more recent times. To this group belong the names of Pixii andSaxton, Holmes and Nollet, Wilde, Varley, Siemens, Wheatstone, andPacinotti, who was the first to discover a means of constructing amachine capable of giving a continuous current always in the samedirection, and which has since proved itself to be the type of nearlyall the direct current electric machines of the present day, andespecially those such as the Gramme and Brush and De Meritensmachines, in which the rotating armature is of annular form; and whenit is considered what a large number of the well known electricgenerators are founded upon this discovery, it must be a matter ofgeneral gratification that the recent International Jury of the ParisExhibition of Electricity awarded to Dr. Antonio Pacinotti one oftheir highest awards.
The original machine designed by Dr. Pacinotti in the year 1860, andwhich we illustrate on the present page, formed one of the mostinteresting exhibits in the Paris Exhibition, and conferred upon theItalian Section a very distinctive feature, and we cannot but thinkthat while all were interested in examining it, there must have beenmany who could not help being impressed with the fact that it tooksomething away from the originality of design in several of themachines exhibited in various parts of the building.
This very interesting machine was first illustrated and described byits inventor in the Nuovo Cimento in the year 1864, under the title"A Description of a Small Electro-Magnetic Machine," and to thisdescription we are indebted for the information and diagrams containedin this notice, but the perspective view is taken from the instrumentitself in the Paris Exhibition.
In this very interesting historical communication the author commencesby describing a new form of electro-magnet, consisting of an iron ringaround which is wound (as in the Gramme machine) a single helix ofinsulated copper wire completely covering the ring, and the two endsof the annular helix being soldered together, an annular magnet isproduced, enveloped in an insulated helix forming a closed circuit,the convolutions of which are all in the same direction. If in such asystem any two points of the coil situated at opposite ends of thesame diameter of the ring be connected respectively with the two polesof a voltaic battery, the electric current having two courses open toit, will divide into two portions traversing the coil around each halfof the ring from one point of contact to the other, and the directionof the current, in each portion will be such as to magnetize the ironcore, so that its magnetic poles will be situated at the points wherethe current enters and leaves the helix, and a straight line joiningthese points may be looked upon as the magnetic axis of the system.From this construction it is clear that, by varying the position ofthe points of contact of the battery wires and the coil, the positionof the magnetic axis will be changed accordingly, and can be made totake up any diametrical position with respect to the ring, of whichthe two halves (separated by the diameter joining the points ofcontact of the battery wires with the coil) may be regarded as made upof two semicircular horseshoe electro-magnets having their similarpoles joined. To this form of instrument the name "Transversal electromagnet" (Eletro calamita transversale) was given by its inventor, towhom is undoubtedly due the merit of having been the first toconstruct an electro-magnet the position of whose poles could bevaried at will by means of a circular commutator.
By applying the principle to an electro-magnetic engine, Dr. Pacinottiproduced the machine which we illustrate on the present page. Thearmature consists of a turned ring of iron, having around itscircumference sixteen teeth of equal size and at equal angulardistance apart, as shown in Fig. 1, forming between them as manyspaces or notches, which are filled up by coiling within them helicesof insulated copper wire, r r r, in a similar manner to that adoptedin winding the Brush armature, and between them are fixed as manywooden wedges, m m, by which the helices are firmly held in theirplace. All the coils are wound round the ring in the same direction,and the terminating end of each coil is connected to the commencingend of the next or succeeding helix, and the junctions so made areattached to conducting wires which are gathered together close to thevertical shaft on which the armature ring is fixed, passing throughholes at equal distances apart in a wooden collar fixed to the sameshaft, and being attached at their lower extremities to the metalliccontact pieces of the commutator, c, shown at the lower part of Fig.3, which is an elevation of the machine, while Fig. 4 is a plan of thesame apparatus.
The commutator consists of a small boxwood cylinder, carrying aroundits cylindrical surface two rows of eight holes, one above the other,in which are fitted sixteen contact pieces of brass which slightlyproject above the surface of the wood, the positions of those in theupper circle alternating or "breaking joint" with those in the lower,and each contact piece is in metallic connection with itscorresponding conducting wire, and, therefore, with the junction oftwo of the helices on the armature. Against the edge of the commutatorare pressed by means of adjustable levers two small brass contactrollers, k k, which are respectively connected with the positive andnegative poles of the voltaic battery (either through or independentof the coils of a fixed electro-magnet, to which we shall presentlyrefer), and the magnetic axis of the ring will lie in the same planeas the line joining the points of contact of the battery and rotatinghelix, this axis remaining nearly fixed notwithstanding the rotationof the iron ring in which the magnetism is induced.
In the apparatus figured in Figs. 3 and 4, the armature rotatesbetween the two vertical limbs, A B, of a fixed electro-magnetfurnished with extended pole pieces, A A, B B (Fig. 4), each of whichembraces about six of the armature coils. The fixed electro-magnet isconstructed of two vertical iron cylindrical bars, A and B, united attheir lower extremities by a horizontal iron bar, F F, the one beingrigidly and permanently attached to it, while the other is fastened toit by a screw, G, passing through a slot so that the distance of thepole pieces from one another and from the armature ring is capable ofadjustment.
The connections of the machine, which are shown in Fig. 3, are made asfollows: The positive current, entering by the attachment screw, h,passes by a wire to the right hand commutator screw, l, to theright-hand roller, k, through the commutator to the ring, aroundwhich it traverses to the left-hand roller, kĻ, and screw, lĻ, tothe magnet coil, A, and thence through the coil of the magnet, B, tothe terminal screw, h, on the right hand of the figure. This methodof