Callan, Nicholas Joseph (1799–1864), priest and pioneering scientist in electrical science, was born 22 December 1799 at Darver, between Drogheda and Dundalk, Co. Louth, third youngest among seven children of Denis Callan, farmer, and Margaret Callan (née Smith). His parents married in the last quarter of the eighteenth century and reared their family near Dromiskin village. The Callans were a well-to-do family who farmed extensively and were also bakers, maltsters, and brewers. He received his early education at Dundalk Academy, went on to Navan seminary for initial preparation for the priesthood, and in 1816 entered the national seminary at Maynooth. During his third year there, he studied natural and experimental philosophy under Dr Cornelius Denvir (qv), who introduced him to electricity and magnetism and exerted a strong influence on the young man. Callan completed his theological studies in 1822 and was ordained a priest on 24 May 1823.
He was sent to Rome (1824), where he attended the Sapienza University and was conferred with a doctorate in divinity (1826). During his time in Rome, he became acquainted with the work of the pioneers in electricity, Luigi Galvani (1737–93) and Allesandro Volta (1745–1827), who invented the first electrical cell (battery). When his former professor, Dr Denvir, resigned, Callan applied for the position and on 15 September 1826 he was appointed to the chair of natural and experimental philosophy at Maynooth. He was a gifted and enthusiastic teacher. However, he showed his real inventive genius in his researches into electricity, and he made fundamental contributions in three areas – electromagnets and the induction coil; batteries; and electric motors. His main claim to fame is his invention of the induction coil, a device for producing high voltage currents and the forerunner of the step-up transformer, an essential device in the modern world of limitless electrical supply. In 1831 Michael Faraday (1791–1867) discovered electromagnetic induction, which basically means that a changing magnetic field can induce an electrical current to flow in a strip of wire. In 1825 William Sturgeon (1783–1850) invented the electromagnet in which wire is wrapped around a soft iron core and electrical current is passed through the wire, which strongly magnetises the iron core.
Callan combined these two ideas to produce his first induction coil in 1836. He wound two coils of wire, one connected to a low-voltage battery, around an iron core. He discovered that, when the current through the primary coil was interrupted, a high-voltage current was produced in the unconnected secondary coil. Sparks issued between the two ends of the secondary coil of wire. Callan noted that the faster he interrupted the current, the bigger the spark. In 1837 he produced a giant induction machine. He used a mechanism from a clock to interrupt the current twenty times a second. The machine generated 15 in. (38 cm) sparks and an estimated 60,000 volts – the largest bolt of artificial electricity ever seen at the time. Callan published reports of his discovery in 1836 and 1837 (‘On a new galvanic battery’, Philosophical Magazine, 3rd ser., ix (1836), 472–8; ‘A description of an electromagnetic repeater, or of a machine by which the connection between the voltaic battery and the helix of an electromagnet may be broken and renewed several thousand times in the space of one minute’, Sturgeon's Annals of Electricity, i (1836–7), 229–30). At the 1857 meeting of the British Association for the Advancement of Science in Dublin, he vindicated his claim to priority of discovery of the induction coil. His claim (‘On the electrodynamic induction machine’, British Association report, Dublin, pt 2 (1857), 11–13) went unchallenged in his lifetime.
Needing reliable batteries, Callan carried out pioneering work on their development. Batteries contain positive and negative plates. Prior to Callan's improvements, batteries used expensive platinum or unsatisfactory carbon for one plate and zinc for the other. He showed that inexpensive cast iron could be used instead of platinum or carbon. Callan invented the ‘Maynooth’ battery in 1854 and the single fluid cell in 1855. In the Maynooth battery the outer casing was made of cast iron and the zinc plate was immersed in a porous pot in the centre. The Maynooth battery went into commercial production in London.
Callan would connect large numbers of batteries, and once connected 577 together to make the world's largest battery. There were no instruments available to measure voltage or current, so he measured the power of his batteries by the weight they could lift when powering an electromagnet. His best effort lifted two tons and was noted in Encyclopaedia Britannica (8th ed.). Callan's batteries produced very high voltages when connected to his experimental coils of wire. Those coils could give large electrical shocks, and Callan used this as another way of testing battery power. He persuaded his students to take shocks from the coils, and gauged the power of the battery from their reactions. One student, William Walsh (qv), who later became archbishop of Dublin, was rendered unconscious by a shock. The college authorities asked Callan to be more careful with his students, so he switched over to electrocuting turkeys.
In 1838 he stumbled on the principle of the self-exciting dynamo. He found that by moving an electromagnet in the earth's magnetic field he could produce electricity without the aid of a battery. The effect was feeble and he did not pursue it. The discovery is usually attributed to Werner Siemens in 1866. 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 in 1853. He also constructed electric motors, and in 1837 built a small motor to drive a trolley around his lab. He proposed using battery-powered locomotives on the new railways and, with considerable vision, predicted electric light.
William Parsons (1800–67), 3rd earl of Rosse (qv), who built the giant telescope at Birr, was a member of the board of visitors to Maynooth College. The story is told that Callan visited Birr to view the telescope, but for some reason he was not admitted. When later the earl came to Maynooth to see the induction coil, Callan suggested that he should return to Birr and view the coil through his telescope.
Popular with both students and fellow-professors, Callan had a simple unaffected manner and displayed considerable charity towards the poor. He died of natural causes at Maynooth on 10 January 1864. The College Museum at the NUI at Maynooth holds a remarkable collection of old scientific instruments, including many items from Callan's laboratory.
After his death, Callan was largely forgotten by the wider world of science. Maynooth was a theological university and science had a low priority on the curriculum. Callan's pioneering work was easily forgotten in such a setting. His invention of the induction coil was attributed to the German instrument-maker Heinrich Ruhmkorff (1803–77). However, it has been generally acknowledged by the world of science, since the 1953 edition of Sir R. A. Gregory and H. E. Hadley, A class book of physics, that Nicholas Callan was the true inventor of the induction coil. A comprehensive bibliography of his publications may be found in M. T. Casey, ‘Nicholas Callan’, cited below.