Nicholas Callan and the Induction coil

Callan's Induction Coil at the National Science Museum, Maynooth

Nicholas Callan‘s Induction Coil at the National Science Museum, Maynooth

On December 22, 1799, Irish priest and physicist Nicholas Callan was born. Callan invented the induction coil (1836) before that of better-known Heinrich Ruhmkorff. Callan‘s coil was built using a horseshoe shaped iron bar wound with a secondary coil of thin insulated wire under a separate winding of thick insulated wire as the “primary” coil. Each time a battery‘s current through the “primary” coil was interrupted, a high voltage current was produced in the electrically separate “secondary” coil.

Nicholas Joseph Callan entered Maynooth College where he studied natural and experimental philosophy under Dr. Cornelius Denvir who is believed to have introduced the experimental method into his teaching, and had an interest in electricity and magnetism. In 1823,Callan was ordained priest and moved to Rome to study at Sapienza University, obtaining a doctorate in divinity in 1826. In Rome, Nicholas Callan became interested in the works of the pioneers in electricity such as Luigi Galvani and Alessandro Volta. In 1826, Callan was appointed Professor of Natural Philosophy at Maynooth. He further started working with electricity in his basement laboratory at the college.

During the 1839s, Callan was inspired by William Sturgeon and Michael Faraday to work on the idea of the induction coil. In 1936, he invented the first induction coil. An induction coil produces an intermittent high-voltage alternating current from a low-voltage direct current supply. It has a primary coil consisting of a few turns of thick wire wound around an iron core and subjected to a low voltage. Wound on top of this is a secondary coil made up of many turns of thin wire. An iron armature and make-and-break mechanism repeatedly interrupts the current to the primary coil, producing a high-voltage, rapidly alternating current in the secondary circuit.

It is believed that Nicholas Callan invened the induction coil because he needed to generate a higher level of electricity than currently available. He used a bar of soft iron and copper wire wrapped around it. Callan connected the beginning of the first coil to the beginning of the second. Finally, he connected a battery, much smaller than the enormous contrivance just described, to the beginning and end of winding one. He found that when the battery contact was broken, a shock could be felt between the first terminal of the first coil and the second terminal of the second coil.

Back then, Nicholas Callan conducted further experiments and the tests showed that the coil device could bring the shock from a small battery up the strength level of a big battery. He tried to make a bigger coil and with a battery of only 178mm plates, the device produced power enough for an electric shock “so strong that a person who took it felt the effects of it for several days”. Apparently, Callan thought of his work as an electromagnet, however, he actually made a primitive induction transformer. Further, Callan’s induction coil used an interrupter that consisted of a rocking wire that repeatedly dipped into a small cup of mercury. Due to its action, which could make and break the current going into the coil, he called his device the “repeater”. However, it is believed that it was the first transformer. In 1837 he produced his giant induction machine: using a mechanism from a clock to interrupt the current 20 times a second, it generated 380 mm sparks, an estimated 60,000 volts and the largest artificial bolt of electricity then (probably) seen.

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