Upon the electrical experiments to determine the location of the bullet in the body of the late President Garfield; and upon a successful form of induction balance for the painless detection of metallic masses in the human body . und could be heard from the telephone eacii time the batterycircuit was made and broken. Being al)sent from my laboratory, and without facilities forproper experiment, I connnunicated my ideas to Mr. CharlesWilliams, Jr., of Boston, manufacturer of electrical and tele-phonic apparatus, who kindly placed the resources of his largeestablishment at my service; and, at gr
Upon the electrical experiments to determine the location of the bullet in the body of the late President Garfield; and upon a successful form of induction balance for the painless detection of metallic masses in the human body . und could be heard from the telephone eacii time the batterycircuit was made and broken. Being al)sent from my laboratory, and without facilities forproper experiment, I connnunicated my ideas to Mr. CharlesWilliams, Jr., of Boston, manufacturer of electrical and tele-phonic apparatus, who kindly placed the resources of his largeestablishment at my service; and, at great personal inconve-nience, delegated his best workmen to attend to my experiments. Up(^n attempting to devise an appropriate form of apparatusfor the special purpose in view I saw that there were greatpractical difficulties in the way of utilizing the arrangementshown in Fig 1, and it occuried to me that the apparatus ofPrcjf. Hughes might perhaps be employed wath more advantageas the basis of my experiments. In the ordinary form of 5 Hughes induction l)alance four coils are used, as shown in Fig. the agency of a Hughes microphone the ticking of aclock is made to create an electrical disturbance in the voltaic. circuit containing the two primary coils ( AC) and a corre-sponding disturbance is produced by induction in the twosecondary coils (B D) connected with the telephone. If theconnections are so arranged that the currents induced in thetelephone ciicuit l)y the coils A C are in the same direction,the ticking of the clock is heard very plainly, but if they arein opposite directions no sound is perceived. In the latter case the action of one primary coil (A) opposesthat of the other, (C,) and an electrical l)alance results. Ifnow a piece of metal is l>i-ouglit near one pair of <oils (say AB) the balance is disturl)ed and the ti(;king of tlie clock isaudible at the telephone. The arrangement of the coils (A,B, C, D) was the point to be studied, the microphone
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