During the Research and development described below, Bell works with many researches of the day: Prof Hughes of London, Trowbridge of Harvard, Prof Rowland of Johns Hopkins Un., Prof Simon Newcomb of Washington, and the staff at Charles Williams' shop of Boston.
7/00/1879 Bell developes a metal detector from a telephone noise tester and thinks he can detect bullets with it
7/2/1881 GARFIELD IS SHOT, The clock and the race against time starts
  Bell chooses to experiment and develop a metal detector usingProf. Hughes4 coilInduction balance. Bell has onemade up in Boston at the Williams shop.
7/14/1881 Bell arrives in WashingtonD.C. at his Volta laboratory which is very well equipped for electrical experiments.He makes modifications to the circuit elements,such as replacing the microphone witha current interrupter (rheotome) and mounts one pair of coilson a handle so they can be used to search for the bullet.
7/19/1881 Bell switches to usinga large primary coil and a small secondary search coil. This increases the detection rangeto 2 inches
7/20/1881 Dr. Bliss the President's doctor visits Bell's Volta Lab to see the metal detector that usesa variation of Hughes four coilinductor balance.
7/21/1881 Tainter,Bell assistant, begins laboratory experiments to optimizethe Hughes four coil balance. They check coil sizes, coil resistances, coil locations, wire sizes, etc.. They develop tablesand graphs ofthe parameters affecting detectable distances of the four coil method.
7/22/1881 Experiments are made with types, numbers, and arrangement of batteries. DrBliss recommends testing the apparatus on war wounded. Bell tests Lieut. Simpson. indefinite results.
7/25/1881 Prof. Rowland suggests using a condenser across the primary coils, this increases the range of the detector by 1cm.
7/26/1881 In the evening Bell and Tainter bring apparatus the to White House and test it out on the President. They wire up condenser incorrectly.The rheotome, interrupter is acting up etc.They don't find any evidence†† of a bullet.Itís a bust.
7/29/1881 From all the data gathered onthe four coil method over the pastdays Bell decides to switch back to the 2 coil method using†† 1, a low ohm primary. 2, lots of current 3, a flat spiral coil 4, a battery system with low internal resistance5, a condenser across primary†† 6,He and his assistant had also developed a new method in listening to the over tones in the musical note from the interrupter. This combination had helped increase the range up to 5 inches, however; experiments were made with the two coils sitting on the lab table and adjusted by hand in a non portable setup.
7/30/1881 1, On Sat 7/30/1881 the White House requested another metal detector trial. Bell explains that they only have the older equipment which was used on 7/26/1881 in a portable format, the condenser fixed, but that he has just developed a new much more sensitive detector coil set with superior range. He and his assistant have also developed a new method to listen to the over tones in the musical note from the interrupter. This combination has helped increase the range up to 5 inches, however;it is only in a prototype laboratory form. Bell asks for time to mount this new detector in a useable portable device. Dr Bliss chooses to wait for the new device.

7/31/1881 That night they mount the new detector coils in the double block adjustable form,with ebonite locking screws see. They fuss around with mounting and adjusting the coils finally using a hammer for fine tuning.†† Among the troubles is a shorted turn causinga no null condition. After much laborBell contacts DrBliss and tells himthe new device iscrude but works . They are also listening to the over tones which increases the range out to 5 inches.
  In theafternoon Bell tests the new 2 coil deviceby lookingfor a bullet in John McGill.They find it using the new 2 coil circuit and with all the latest improvements but can't find it with the four coil circuit.
8/1.1881 Bell scans the President with the new double coil and its 5 inches range. He couldn't detect the bullet.AN AUTOPSY later showed the the bullet was too deep to be detected†† by Bell's apparatus. IT WAS LATER FOUND TO BE IN A HARMLESS POSITION.Garfield died of infections.
8/2/1881 Bell returnsback to the Mansionto see if the metalmattress caused the problemfinding the bullet andIT WASN'T.
  Bell leaves Washington. Tainter goes on to improve mechanically the instrument. but it really finds little use. X-rays become the preferred means of finding bullets. Bell works on and off in Boston at Williams shop on refinements
8/15/1881 Bell's son dies