Monday, November 01, 2010

The Induction Coil (Part 2)

Not to diminish the roles of Daniel Davis, Benjamin Pike, S.B. Smith, Neef, Wagner, James Foster, and others but they don't really matter much in the narrow scope of this little article. I refer to them only as necessary. I'm skipping ahead to Callan. What's unique about the development of the induction coil is that much of it's improvements happened concurrently, not sequentially. Try to remember that as I mercilessly skip back and forth in the chronology.An 1867 history book summarized my dilemma.
"During that period a very great number of induction coils and circuit-breakers were announced, but no importance or interest seems to have been attached to this branch of the subject. We had the Masson coil, the Neef coil, the Callan coils, the Sturgeon coils, the McGauley coil, the Dr. Bird coil, the Lockey, the Nesbitt, the Clarke, the Roberts, the Bachhoff'ner, and many other coils, all represented as being very potent in giving shocks; but, beyond the intensity required for this purpose, not a single inquiry is recorded."
Of all those, only Callhan is really material as he's directly connected to the other main characters in my narrative.  So let us rewind to 1836. Nicholas J. Callan was was a priest and scientist like Murgas I suppose but clearly more disciplined. He was Professor at Maynooth College near Dublin and most of his work I refer to occurred there.  In 1936 he was 37 years old, and had just developed his first induction coil...it was within months of the one Page invented. In an 1836 issue of the Annals of Electricity His induction coil was described as a transformer. It was a 2-foot long bar of soft iron bent into a horse shoe shape and wrapped with two separate windings: the first was about 200 ft of thick copper wire, and the second outer layer with thin copper wire. He thought it was an electromagnet, much like the one Joseph Henry had made in 1831. More here and here.

But like the others, the first thing he set about doing was shocking himself.  He connected a battery to both ends of the primary coil.  He discovered that when the battery contact was broken, a shock could be felt between the first terminal of the primary coil and the unconnected end of the secondary coil.  But he did something interesting with it. He engineered a way to break and reconnect that circuit quickly with a device he called a "repeater." He used a hand crank that turned a cog wheel that connected to a horizontal copper rod via an escapement that made connection with the wheel. With it he was able to break and make the circuit over 500 times a second. This generated some massive sparks. He experimented with more and more powerful battery configurations until his peers were afraid of his works. He described it  in the 1836 July-December issue of the London and Edinburgh Journal of Science.
"By experiments on the best means of obtaining the shock from the electromagnet, I have found that the shock increases, within certain limits, with the length and thinness of the bar of soft iron, and with the length of the helical coil, as far perhaps as 200 feet, and in proportion, or nearly in proportion, to the number of plates in the voltaic battery from which the current of electricity is passed through the helix. The shock does not increase in proportion to the number of plates unless they are large. ... the shock was so strong that a person who took it felt the effects of it for several days. ... I could not induce any one to take the shock from the electromagnet when a greater number than 16 of our large plates were used."
Later  Callan's experimented with an induction coil using toughs of mercury just like Page. His was arranged with a wire that was rocked repeatedly into the mercury. Ultimately Callan determined (at least tactility) that the faster he interrupted the current, the bigger the spark. In 1837 he build a large scale induction device It generated 15-inch sparks, which are estimated to have produced up to 600,000 volts which was the largest artificial bolt of electricity ever made.
He didn't toil in total obscurity. Callan did publish papers on his primary works allowing others to build on them. In 1837, Callan sent a replica of his coil to William Sturgeon and it was exhibited to members of the Electrical Society.  Sturgeon (as noted previously) may have invented the first electromagnet in 1825. His was a horseshoe-shaped piece of iron that wrapped with a loosely wound copper coil. Sound familiar?  Well as much as Sturgeon had been inspired by Page, he also has an earlier position on this Mobius strip. In 1830, Joseph Henry (of the Henry Calorimeter) held a demonstration Sturgeon's electromagnet.  He used a battery to send an electronic current over one mile of wire activating an electromagnet which triggered an armature that then struck a bell.  I don't want to overstate things.. but that is the basic mechanism in the telegraph...

Despite the reception of his 1837 paper, he did not publish often. And because his college was a theological school, his colleagues often tried to dissuade him in science pursuits. He experimented with galvanization and different batteries but did gradually stray away from his greatest contributions. He died in 1864, about 40 years before he'd be recognized scientifically for his contributions.