The Hidden-Metal Detector
by Bruce B. Abbott

[preliminary version, January 2001]

Probably sometime around late 1927, my grandfather, Raymond B. Abbott, Sr. was approached by Shirl Herr, a Crawfordsville, Indiana businessman and inventor, for help in further developing his idea for a hidden-metal detector. My grandfather received financial support from Shirl for this purpose and the result was what I believe to be the world's first portable metal detector. The photograph to right shows a Mr. Leonard trying out the detector, with my grandfather close behind, gripping the electronics/battery box that powered the detector.

Whose Invention Was It?

I have two versions of the story concerning the Herr-Abbott collaboration. According to Eleanor Herr, widow of Shirl's son Remley Herr, the device was already completed and Shirl came to my grandfather for help with the patent application, owing to Shirl's lack of familiarity with the technical terms needed to describe the device in the application. My father's version of the story is that Shirl had the basic idea but sought technical assistance in developing the idea into a practical, working device. This my grandfather did, with Shirl's financial assistance. When it was decided to apply for a patent, Shirl insisted that the patent be taken out in my grandfather's name, but Ray stubbornly insisted that it be taken out in Shirl's name. This standoff was resolved when Shirl offered to take out the U. S. Patent and give Ray the rights to any foreign patents, and Ray accepted.

So to whom goes the credit for the invention? I suspect that both stories are correct in part.

Shirl Herr did apply for a U. S. patent for his "hidden-metal detector," but it was not the device shown being demonstrated in the photo. Shirl's patent was applied for on February 4, 1924, a date that probably preceeds the Herr-Abbott collaboration, and was granted on July 31, 1928 (U. S. Patent No. 1,679,339) -- see diagram at right. On January 22, 1928, my grandfather presented a public lecture on "Geophysical Prospecting" at the Purdue Physics Building. Furthermore, he published an abstract entitled "Magnetic Reflection" in the February issue of Physical Review that same year. This article describes the technology found in Shirl's later device: a transmitter electromagnet coil being driven at 500 Hz, a larger, flat loop coil located some distance away and oriented so that the magnetic field of the first coil produces no current in the second, and an amplifier and telephone receiver connected to the second coil. The device described in Shirl's patent has a self-breaking relay that rapidly pulses a small electromagnet coil and a larger, flat surrounding coil lying concentric with the first and also oriented so as to null out any current, and a telephone receiver. Thus it lacks two features of the Abbott apparatus, namely the amplifier and the separation of the coils by a "fair distance." Both of these features were apparently present in the device pictured in the photo.

As Shirl applied for his patent well in advance of Ray's work on magnetic reflection, it is not likely that Ray was consulted merely for his knowledge of the correct technical terms to use in the application. It is more likely that Shirl had already applied for his patent and wanted to develop a more sensitive version of his device, but lacked the electronic know-how to do so and hired my grandfather for this purpose. I do not know whether the more advanced device was ever patented.

How the Device was Used

My father tells me that the box containing the electronics and batteries (Remley called it the "buzzer box") had to be kept well away from the detector and directly behind it, or else it would generate an interference. Dad remembers being given the job of carrying the buzz box and having to wander all over the place to keep it properly oriented behind the detector. He told me that his father had to wear a pair of tennis shoes with the metal grommets removed in order not to set off the device.

Eleanor Herr told me that power for the device came from perhaps four "old fashioned" storage batteries that were mounted in the buzzer box. I suspect that they didn't last long powering tube-type electronics. Dad remembered that the two coils were mounted on opposite ends of the horizontal bar extending from the vertical handle that Shirl is seen holding in the photo. The electromagnet coil was mounted in the rear and the larger detector coil in the front. In the photo one can see that the telephone receiver has been replaced by a headphone set.

Prospecting for Buried Treasure

One of the first uses of the detector was to locate the outlines of an old fort that had once existed near West Lafayette, Indiana. The wood of the fort had been held together with square iron nails, and the iron traces of these nails provided the means by which the outlines of the fort's perimeter were traced. Also found in this area were the remains of a Native American "princess," so named because she had been found buried with pots and jewelery which suggested that she was relatively wealthy.

At some point my grandfather took the apparatus to Arizona, where it was used to prospect for pieces of the iron meteor that formed Barringer Crater. A fire-burned portion weighing about eight pounds was located and taken back to West Lafayette. It was later cut into three pieces, two of which are still in possession of my father.

Shirl and my grandfather took the device to Pennsylvania and there were able to locate the encampment of General Braddock, which took place during "Braddock's Retreat." To keep their arms from falling into the hands of the enemy, canonballs had been split and anything that could not be carried was buried at the campsite. The iron in those materials revealed the location of the encampment, which turned out to be some distance from where historians had thought it to be. Items discovered by the detector were dug up and turned over to the local museum, where they remain on display.

According to Eleanor Herr, Shirl and Remley went to Europe with the device just as Muselini was coming into power in Italy. There was archeological work being done on the remains of Caligula's Barge, which had been located underwater near shore. Eleanor told me that Shirl visited this site and got so excited when it registered the presence of metal that he lost his balance and fell into the water. Several men jumped in to rescue him, and all emerged covered with leaches, which then had to be removed one by one. In England some prospecting was done at Stonehenge and an artifact located which was turned in to the British Museum. At the time it was believed to be of relatively recent origin but according to Eleanor, Remley later heard that additional artifacts were discovered at this site and that their ages had been found to be much older than originally thought.

My father tells me that the local newspaper was skeptical about the ability of the machine to locate metal, so my grandfather arranged for a demonstration. He had the newspaper officials bury several silver dollars and challenge local "dowsing-rod" champions to find them. When they had failed, grandfather fired up the detector and rapidly located all of them. Apparently this publicity alerted Lafayette officials to the existence of the device and grandfather was called upon to use it to relocate the water pipes buried beneath the streets of the town.

Another story about the detector told to me by my father is that it was called upon to help locate a nail that had been swallowed by a cow. Cows have four stomachs and the vet was reluctant to operate not knowing in which stomach the nail resided. The detector succeeded in locating the nail but unfortunately it was already too late to save the cow. (This episode is reminiscent of the Garfield incident described later.)

Admiral Byrd

Eleanor Herr has in her possession a framed letter from Admiral Byrd, thanking Shirl for the use of his metal detector during one of Byrd's famous expeditions to Antarctica. Supplies were buried under the snow on the way out from the base camp and the detector apparently was used to relocate them on the return trip.

Final Resting Place

so what has happened to the world's first portable metal detector? Sadly, it no longer exists. According to Eleanor, it was given to her son-in-law, who intended to restore the device to working order after years of neglect. This proved difficult owing to the antiquity of the electronics and batteries, and apparently it was eventually deemed not worth the trouble. When the son-in-law moved to a new house, the detector went out with the trash.

Other Claims of Priority

Apparently the first metal detector was developed by Alexander Graham Bell around 1890 and was said to have been used in an attempt to locate the bullet that had entered President Garfield's body durin an assasination attempt. The bullet was not found and Garfield died a short while later.

The company founded by Gerhard Fisher claims that Fisher was the first to develop a portable metal detector, which was sold commercially beginning in 1931. This would have been three years after the second-generation Herr machine was up and running and seven years after Shirl had applied for a patent on his original device. So unless there is proof that Fisher had developed his unit earlier than 1924 (or by 1928 at the latest), the prize for first-ever portable metal detector must go to Shirl Herr. Fisher's claim to fame may be, not that he developed the first, but that he was the first to market one.