[LB011257], Letter from Richard Nott Dyer to Thomas Alva Edison, February 14th, 1882
The following are my news on Siemens's English patent  of 1873, with special reference to the 2d and 4th claims, which your electrical generators (both large and small) are stated to infringe by Dr. J. Hopkinson in a report dated 11th Novr 1881.##2nd claim - ##"The use of apparatus of the kind above referred to in which the wire instead of being coiled along a shell is coiled longitudinally over the external surface of an iron cylinder which is made to revolve within magnetic poles or poler extensions, substantially as herein described."##It was old at the date of this patent to provide a cylindrical armature core with a bobbin of wire wound longitudinally along the same kind crossing its ends, but only covering part of the external surface of the cylindrical core. This bobbin had been arranged in one end in two coils.##[Original Siemens armature, (patent 2107-1856), and Fergussons' machine, (Journal of Science, Vol. XIII page 427)]##It was also old to cover the entire effective external surface of a cylinder with wire, wound longitudinally along the same and returning through the interior of the cylinder.##[Gramme Patent 1668-1870]##Taking these facts into consideration, there would hardly be ingenuity amounting to patentable invention in the bold idea of covering the entire surface of a cylindrical core with longitudinally wound wire crossing the ends of the core. Whether the wires cross the ends of the core or pass through it, is a matter relating wholly to the connections the effective wire being located the same and the effect being essentially the same in both cases.##If the same connections exactly were used in the new Siemens machine that are used in the Siemens machine of the oreiginal type, no ingenuity at all would have been exercised in making the change from a partly covered cylinder to one wholly covered with wire. And since the entire effective external surface of a cylinder had been before covered, and connections of one kind described, the Siemens invention must relate to connections of anotherkind. Hence to give the 2nd claim the substance of patentable novelty (if it has that in any sense), it must include the connections described in the patent, which are necessary to make the machine an operative and useful one.##There are two general ways of making the connections explained in the complete specification, viz:##(1) The connectin of the ends of each coil with separate commutator plates or springs, the coils not being connected together, as especially described in connectin with figures 4 of the drawing.##(2) The continuous winding shown in figure 8, the coils being connected together, and all the coils being continuously in circuit.##The second claim then has a dual nature, and the question of infringement by your machine is reduced to a consideration of these two windings.##The first winding is not found in any of your machines.##The second winding is probably used in yoiur small wire-wound armatures.##(Note - the bearing of the 2nd claim upon your large machines or those employing bars and disks, is discussed further on.).##But it is doubtful if his second winding is sufficiently [foreshadowed] or described in the provisional specification.##The provisional throughout seems to refer to the first winding only, it being stated & brought out that the coils are brought suscessively into circuit. The connection of the coils together is now here mentioned; but the different effects obtainable are described as due to their connection with the commutators, or the arrangement of each separate coil, and its commutator plates with relation to the commutator brushes (or poles of machine), and the poles of the exciting magnet.##The description at line 10 page 2, (referred to by Dr. Hopkinson under 4th claim) undoubtedly relates to the first winding exclusively, since further on in the same paragrah it is stated that [---] causing the shell with its coil to rotate by mechanical force, currents of electricity are generated in the coils as they successively pass the fixed magnetic poles, and by properly arranging the conductor from these several coils in relation to the poles of the magnet, and to the conductors on which they bear in their rotation, these electric currents are transmitted through any conductor connecting the poles of the machine."##And again in next sentence - "The currents thus transmitted may be made either continuous or intermittant in one direction, or they may be made alternately reversed by suitably arranging the conductors from the several coils in relation to commutators, connecting them successively during their rotation with the poles of the machine."##If the second winding is anywhere described in the provisional, it is in paragraph commencing with line 34 page 2. The following is the pertinent part of that paragraph.##"The wire may be coiled at the shell in two layers over an even number of divisions of the perphery of the shell, the two opposite divisions in each case having the same wires, but the ends of those wires being connected successively to insulated conductors in number equal to that of the divisions of the shell, which conductors revalue with the shell and come successively to bear against two fixed springs, rollers, or conducting brushes forming the poles of the machine. The connections of the several wires to these several conductors may be so arranged that a continuous current is produced by the rotation of the shell."##This paragraph is very indefinite, and it is doubtful what it does describe. The statements contained by it are not repugnant to the theory that the winding intended to be described embodies the general features of the first winding extended to two layers of wire.##On 4th page, line 5, the following statement is made which should be considered in the reading of the paragraph under discussion.##"In apparatus such as have been described the successive coils have to be brought successively into connection with the main circuit, by means of conductors or contact makers, which the ends of their wires successively pass in their rotation."##This refers to all apparatus before described. If the paragraph commencing with line 34, page 2, were intended to describe a winding in which all the coils are kept continuously in the main circuit, the exception would have been noted at this point, and especially since the construction described after the words last quoted, for maintaining control with one commutator plate until contact is made with the next succeeding one, so as not to cause a break in the circuit, is as applicable to the second winding as to the first.##At an intermediate point in the provisional, in the next paragraph following the one under discussion (page 3 line 18), is the following, referring to a modification##"xxx a cylindrical shell of iron, having insulated wire wound round it xxxx in a number of separate coils, each of which is connected to conductors in the manner described above. This cylindrical iron shell being caused to rotate xxx, currents of electricity are caused to pass along the wires coiled along it successively as each coil passes through one of the magnetic fields, and these currents are transmitted either directly or by commutators as above described to the main poles of the machines."##Again, referring to another modification (page 3 line 34)##"By this arrangement the successive coils on the cylindrical iron shell are made to pass in each revolution of the shell through more than two magnetic fields, and consequently a more rapid succession of currents is given [a [led] by them."##Upon careful consideration of the whole patent, I am inclined to advance the opinion that the second winding is not described at all in the provisional, or if intended to be referred to, is not described so as to distinguish it from the first winding or establish it s identity as a separate invention, and for that reason is not sufficiently [furnish advasned] in the provisional.##If this new is a correct one, your machines do not infringe the 2nd claim of Siemens's patent, and it will be necessary for Siemens to disclaim the second winding to make his patent valid for these features that are sufficiently described.##4th claim##"The method substantially as herein described in reference to page 4 and 8, Sheet I, of coiling the wires of the shell of apparatus such as is referred to above, whether such wires are single or in duplicate, and of connecting them to the poles of the apparatus."##This claim is specifically for the two windings, the first of which is not infringed by you and the second of which is probably not sufficiently described in the provisional specification, and is therefore not legally covered by the claim.##If I am correctly informed, Siemens wound the armaturesof his machines according to the first winding for some time after the provisional specification was filed, and upon that winding proving a failure, the second winding was adopted. If that is a fact, it is quite a strong confirmation of my view of the provisional with respect to the second winding.##Anticipation by Gramme.##The opinion already advanced by you that the second winding of Siemens is simply the continuous winding of Pacinotti and Gramme, with the connections of the coils crossing the ends of a cylinder, instead of passing through it (the same result being obtained in both cases) seems to me the strongest ground that can be taken against the Siemens 73 patent, in the event of finding that the second winding is sufficiently foreshadowed in the provisional.##The Gramme patent (1668 1870) describes the combination of cylinder and continuous winding, the only difference from Siemens being that in one the effective wire is connected through the inside of the cylinder, while in the other the connection is made directly across the end of the cylinder; but in view of the state of the art, as set forth in the first part of this letter, this difference might be considered lacking in ingenuity amounting to patentable invention.##Bobbin of bars and disks.##Proceeding, for the purposes of this part of the discussion, upon the hypothesis that the second wrinding is sufficiently foreshadowed in the provisional (which however is not admitted as a fact), it becomes important to determine whether your large machines, having bobbins composed of longitudinal bars and cross connecting disks, as well as the small wire-wound machines, infringe the 2nd and 4th claims of the Siemens patent.##In the construction of armatures for machines of this class, bars are practically an entirely different thing from wire. They cannot be twisted around the shaft at the ends of the armature and laid over each other, or connection sections so as to take exactly the same course as the wires, for the reason that theya re altogether too bulky. If bars were simply substituted for wires and placed in the core i the same way, they might be considered the equivalent of coiled wire, but this cannot be done in practice. You do not use simply coils composed of bars instead of wires, but coils composed of longitudinal inductive bars and cross connecting disks. By this construction you obtain an exceedingly low resistance in a compact form, adapted for the rapid conduction of heat from the effective conductors, the construction is wholly mechanical and the winding symmetrical, there is no local cutting at the ends of the armature, as would be the case if bars were used in place of the disks, ready access is given to the parts for inspection, and repairs may be made without tearing apart the bobbin, all of which are features that are highly important if not essential in the economical manufacture of large and efficient machines.##Another important feature is that by using bars and disks, the resistance at the ends of the armature in the useless portion of the conductor can be reduced to any desired extent, whereas with wire the same cross section of conductor must be continued throughout.##The disks form multiple arc connections between the bars affording two paths for the current from one bar to another - one path around each side of the shaft. ##For these reasons the bars and disks are different both mechanically and electrically from coiled wire.##They are also in my opinion not the legal equivalent of coiled wire; but form a distinct and independent advance in the art, which makes possible the economical construction of large and efficient machines.##The 2nd and 4th claims of Siemen's patent each calls for coiled wire, which as before shown, does not include the construction employing bars and disks.##I therefore conclude that your large machines, or those in which the bobbins are composed of bars and disks, would not infringe Siemens's patent, even if such patent were found to be a good and valid patent to the extent of its claims.
[LB011257], Letter from Richard Nott Dyer to Thomas Alva Edison, February 14th, 1882
Thomas A. Edison Papers, School of Arts and Sciences, Rutgers University