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 . The outer coil being of coarse wire (No. 18) placed in the primary circnit, the inner coil l)eing of very tine wire (No. 36) ami connected with a telephone. The parallel cm-rents traversing the wires neutralized each otlier, and no audible effects are perceived in the telephone, but on presenting a metallic hody to the instrument npon a line bisecting the angle betwee
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 . The outer coil being of coarse wire (No. 18) placed in the primary circnit, the inner coil l)eing of very tine wire (No. 36) ami connected with a telephone. The parallel cm-rents traversing the wires neutralized each otlier, and no audible effects are perceived in the telephone, but on presenting a metallic hody to the instrument npon a line bisecting the angle between the coils the clicking in the telephone is heanL This instrument possesses only one advantage ovci that^ sent, and that is that it requires no adjustment. See Ajipeudix, notes .\ uiul 1. The other iii^truiuent consists of two Lu-) phiced upon opposite sides of a coil of coarse wii-e, (No. 1^,) tlie fine coil Ueiiiii connected so that the induced cnn-ents ncnti-alizc each othei, tluis: Fig. 4,. I am sorry to he - telephones of the l)est con- struction must l)e used. As I stated in the first instance, if the ball is more than two inches deep, I tliink it cannot he located by this means. If larger coils were used the instrument miglit l)e operative at a greater distance, hut the area indicated as containing the l)all would he so hirge that the result would he indetinite and without value. Hoping that Prof. Bell will he able to succeed, I remain, Yours very truly, Geo. M. Hopkins. Prof. Hughes of London, England, Prof. Trowbridge ofHarvard College, Prof. Rowland of Johns Hoi>kins Univei-sity,and other authorities were consulted by telegraph as to the besttheoretical form of induction balance for the purpose i
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