[LB011379], Letter from Richard Nott Dyer to Lemuel Wright Serrell, March 6th, 1882


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[LB011379], Letter from Richard Nott Dyer to Lemuel Wright Serrell, March 6th, 1882

Editor's Notes

Your letter of 2d inst., to Mr Edison relating to the rejection of 1st claim in German Case no. 7. has been turned over to me for answer.##This claim is undoubtedly the most important in the case, and every ossible effort should be made to obtain it. The appeal of course should be taken.##The claim is not broadly for the division of the armature core longitudinally to reduce the formation and circulation of [forcault] currents, but for a pecular way of doing this. the claim should not therefore be considered as covering a principle broadly, but only a highly efficient construction for carrying out a principle before applied in a different form. The claim is limited to thin annular disks of metal, with thin interposed insulating material, the whole being clamped or secured together in a solid mass upon a shaft or hub.##The loss by generation of heat in the armature core of a dynamo or magneto electric machine is in proportion to the extent & of the separate magnetic parts of the core in the direction of the length of the core - that is the cutting length of each part with relation to the lines of force. The disks used by Mr Edison being very thin, the cutting of the lines of force is reduced to an infinitesimal factor. In addition the fact that the disks and interposed insulation are secured solidly together, makes the peculiar core as well adapted for very large machines, where great strength is required, as for small ones. ##It will be readily seen that the use of brushed wires, or of thick plates, separated by air spaces, for this purpose is not the same thing practically. The brushed wires, if not insulated, (the usual construction in Gramme rings) do not prevent entirely the circulation of thousand currents and they are much thicker than the individual disks of Mr Edison whether insulated or not. They do not make a core that is as cheap, or as solid and strong, as one made like Mr Edison's The thick plates separated by air spaces allow the generation and circulation of [Foucault] currents to a great extend. The air spaces are provided to premit the circulation of air to carry off the heat which is generated by the thickness of the plates, while Mr Edison's construction does not require the use of air spaces through the core. The thick plates separated by air spaces do not form as strong or as efficient a core as Mr Edison's construction. Mr Edison's construction is the only one theoretically correct recognizing the fact that the extent of material lengthwise of core, is detrimental, while diametrical extent is beneficial, in that it gives indicators strength and solidility.##In regard to foreign materials generally, I wish to inform you that Major Wilber is no longer looking after them, and to request that in the future you would address all letters relating to that subject either to Mr Edison personally or to myself.




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Thomas A. Edison Papers, School of Arts and Sciences, Rutgers University
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