His local parish priest, Father Andrew Levins, then took him in hand as an altar boy and Mass server, and saw him start the priesthood at Navan seminary.

[1] Callan was ordained a priest in 1823 and went to Rome to study at Sapienza University, obtaining a doctorate in divinity in 1826.

In 1826, Callan returned to Maynooth as the new professor of natural philosophy (now called physics), where he also began working with electricity in his basement laboratory at the college.

[2] Influenced by William Sturgeon and Michael Faraday, Callan began work on the idea of the induction coil in 1834.

It has a primary coil consisting of a few turns of thick wire wound around an iron core and subjected to a low voltage (usually from a battery).

With a battery of only 14 seven-inch (178 mm) 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".

In 1837 he produced his giant induction machine: using a mechanism from a clock to interrupt the current 20 times a second, it generated 15-inch (380 mm) sparks, an estimated 60,000 volts and the largest artificial bolt of electricity then seen.

Callan also discovered an early form of galvanisation to protect iron from rusting when he was experimenting on battery design, and he patented the idea.

The Callan Building on the north campus of NUI Maynooth, a university which was part of St Patrick's College until 1997, was named in his honour.

In addition, Callan Hall in the south campus, was used through the 1990s for first-year science lectures including experimental & mathematical physics, chemistry and biology.