scientific evidences stating meucci's priority on bell anti sidetone circuit meucci began investigating topics related with the telephone system in as shown by a drawing of the same year reproduced below this drawing formed the basis for meucci's caveat of but as meucci's lawyer did not file it with the caveat it was later notarized by meucci himself in his affidavit of october the drawing shows a two way simultaneous telephone conversation with a complete separation between the two directions of transmission indicated by arrows this contrivance is aimed to counteract the so called side tone effect that is the hearing of the echo of the speaker's own voice as well as any background noise in his own receiver this layout is known today as a four wire circuit with it meucci anticipated any other inventor as proved by the following no mention of side tone effects nor measures to counteract it are found in bell's patents nor in gray's caveat both of in the first bell's subscriber lines the four initially two instruments were simply put in series on the same line the first anti sidetone ast circuits were introduced by the bell people in the s particularly by george a campbell with his nine patents of many decades after meucci's solution was shown in this drawing and over thirty years after the same drawing was notarized inductive loading the drawing reproduced above is taken from a note jotted down by meucci in his laboratory notebook on september and reported in an affidavit by m lemmi of september containing the english translation of said notebook see also my paper on antenna it can be seen that diagrams no and no differ from no in the insertion midway along the long distance line of an inductor with either a horseshoe or bar iron core in diagram no the inductor is split into two parts inserted at both ends of the line in his notes meucci pointed out that in this way he could get rid of the battery and that by splitting the inductor he obtained better results this technique is known today as the inductive loading of long distance telephone lines allowing to increase the distance and or the quality of speech the proof that meucci came first can be drawn from the following events occurred many years after meucci's discovery or its notarization in june july oliver heaviside and alfred vaschy predicted on the basis of mathematical calculations that telephone signals could be transmitted without distortion by increasing the line's self induction on june m i pupin obtained the first two patents for said technique the bell telephone co acquired both patents and later on applied them in its lines means to counteract the skin effect because of the increased bandwidth of the telephone with respect to the telegraph telephone lines were subjected to increased attenuation due to the so called skin effect in two notes of in his laboratory notebook notarized in lemmi's affidavit of meucci suggested to treat the surface of the copper conductor in various ways basically with graphite to increase its surface conductivity moreover in his caveat of meucci stated i believe it preferable to have the wire of larger area than that ordinarily employed in the electric telegraph another note in his notebook dated august reads to be adopted for having long distance bundles of copper wire insulated with cotton or any other kind of wrapper by this means i have obtained a distance of about one mile for this bundle of copper wires meucci filed a us patent application wire for electrical purposes on july that meucci was first in said techniques is proven by the following facts skin effect in telephone lines was neglected by all inventors till when it began to be investigated by david e hughes and oliver heaviside following their studies and the development of hard drawn copper the bell telephone co decided to use copper in place of steel beginning from the boston new york line which was inaugurated on march call signaling meucci adopted a telegraphic call signaling simply effected by a morse key attached to each end of the line momentarily short circuiting the local transmitter in this way strong pulses of current were sent along the line and the distant receiver would emit intermittent ticks much louder than the ordinary speech in his caveat of meucci gave a detailed description of his call signaling consistent w