These wet cells had to be topped up with water from time to time; but the little dry cells in our torches were clearly different. Marcus, seeing my interest, dissected one for me, using his powerful scout knife, showing me the outer case of zinc, the central carbon rod, and the rather corrosive and strange-smelling conducting paste between them. He showed me the massive 120-volt battery in our portable radio (this was a necessity in the war, when the electricity supply was so erratic) – it contained eighty linked dry cells, and weighed several pounds. And once he opened the bonnet of the car – we had the old Wolseley at the time – and showed me the accumulator, with its lead plates and acid, and explained how this had to be charged, and could carry a charge repeatedly, but not generate one itself. I adored batteries, and they did not have to be live; when my interest was made known to the family, used batteries of all shapes and sizes poured in, and I rapidly accumulated a remarkable (though wholly useless) collection of the things, many of which I opened and dissected.
But my favorite remained the old Daniell cell, and when we went modern and got a natty new dry cell for the bell, I appropriated the Daniell for myself. It had only a modest voltage of 1 or 1½ volts, but the current, several amperes, was considerable in view of its size. This made it very suitable for heating and lighting experiments, where one needed a substantial current, but the voltage hardly mattered.
Thus I could readily heat wire – Uncle Dave had supplied me with a whole bandolier of fine tungsten wire of all different thicknesses. The thickest wire, two millimeters in diameter, became mildly warm when I connected a length of it across the terminals of the cell; the thinnest wire grew white-hot and incinerated in a flash; there was a comfortable in-between wire that one could maintain for a little while at red heat, though even at this temperature it soon oxidized and disintegrated into a fluff of yellowish white oxide. (Now I knew why it had been crucial to remove the air from lightbulbs, and why incandescent lighting was not possible unless the bulbs were evacuated or filled with an inert gas.)
I could also, using the Daniell as a source of power, decompose water if it was briny or acidulated. I remember the extraordinary pleasure I got from decomposing a little water in an eggcup, seeing it visibly separate into its elements, oxygen at one electrode, hydrogen at the other. The electricity from a 1-volt cell seemed so mild, and yet it could suffice to tear a chemical compound apart, to decompose water or, more dramatically, salt into its violently active constituents.
Electrolysis could not have been discovered before Volta’s pile, for the most powerful electrical machines or Leyden jars were wholly impotent to cause chemical decomposition. It would have required, Faraday later calculated, the massed charge of 800,000 Leyden jars, or perhaps the power of a whole lightning stroke, to decompose a single grain of water, something that could be done by a tiny and simple 1-volt cell. (But my 1-volt cell, on the other hand, or even the eighty-cell battery that Marcus showed me in the portable radio, could not make a pithball or an electroscope move.) Static electricity could generate great sparks and high-voltage charges (a Wimshurst machine could generate 100,000 volts), but very little power, at least to electrolyze. And the opposite was so with the massive power, but low voltage, of a chemical cell.
If the electric battery was my introduction to the inseparable relation of electricity to chemistry, the electric bell was my introduction to the inseparable relation of electricity to magnetism – a relation by no means self-evident or transparent, and one that was discovered only in the 1820s.
I had seen how a modest electric current could heat a wire, give a shock, or decompose a solution. How was it managing to cause the oscillating movement, the clatter, of our electric bell? Wires from the bell ran to the front door, and a circuit was completed when the outside button was pressed. One evening when my parents were out, I decided to bypass this circuit, and connected the wires so that I could actuate the bell directly. As soon as I let the current pass, the bell hammer jumped, hitting the bell. What made it jump when the current flowed? I saw how the bell hammer, which was made of iron, had copper wire coiled around it. The coil became magnetized when a current flowed through it, and this caused the hammer to be attracted to the iron base of the bell (once it hit the bell, it broke the circuit and fell back into its original place). This seemed extraordinary to me: my lodestones, my horseshoe magnets, were one thing, but here was magnetism that appeared only when a current flowed through the coil, and disappeared the moment it stopped.
It was the delicacy, the responsiveness, of compass needles which had first given a clue to the connection between electricity and magnetism. It was well known that a compass needle might jerk or even get demagnetized in a thunderstorm, and in 1820 it was observed that if a current was allowed to flow through a wire near a compass, its needle would suddenly move. If the current was strong enough, the needle could be deflected ninety degrees. If one put the compass above the wire rather than below it, the needle turned in the opposite direction. It was as if the magnetic force were forming circles around the wire.[35]
Such a circular movement of magnetic forces could readily be made visible by using a vertical magnet sticking in a bowl of mercury, with a loosely suspended wire just touching the mercury, and a second bowl in which the magnet could move and the wire was fixed. When a current flowed, the loosely suspended wire would skitter in circles around the magnet, and the loose magnet would rotate in the opposite direction around the fixed wire.
Faraday, who in 1821 designed this apparatus – in effect, the world’s first electric motor – immediately wondered about its reverse: if electricity could produce magnetism so easily, could a magnetic force produce electricity? Remarkably, it took him several years to answer this question, for the answer was not simple.[36] Putting a permanent magnet inside a coil of wire did not generate any electricity; one had to move the bar in and out, and only then was a current generated. It seems obvious to us now, because we are familiar with dynamos and how they work. But there was no reason at the time to expect that movement would be necessary; after all, a Leyden jar, a voltaic battery, just sat on the table. It took even a genius like Faraday ten years to make the mental leap, to move out of the assumptions of his time into a new realm, and to realize that movement of the magnet was necessary to generate electricity, that movement was of the essence. (Movement, Faraday thought, generated electricity by cutting the magnetic lines of force.) Faraday’s in-and-out magnet was the world’s first dynamo – an electric motor in reverse.
It was curious that Faraday’s two inventions, the electric motor and the dynamo, discovered around the same time, had very different impacts. Electric motors were taken up and developed almost at once, so that there were battery-powered electric riverboats by 1839, while dynamos were much slower to develop and became widespread only in the 1880s, when the introduction of electric lights and electric trains created a demand for huge amounts of electricity and a distribution system to keep them going. Nothing like these vast, humming dynamos, weaving a mysterious and invisible new power out of thin air, had ever been seen, and the early powerhouses, with their great dynamos, inspired a sense of awe. (This is evoked in H.G. Wells’s early story ‘The Lord of the Dynamos’, in which a primitive man begins to see the massive dynamo he looks after as a god who demands a human sacrifice.)
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A discovery that for some reason especially interested me was Faraday’s discovery of diamagnetism in 1845. He had been experimenting with a very powerful new electromagnet, placing various transparent substances between its poles to see whether polarized light could be affected by the magnet. It could, and Faraday now found that the very heavy lead glass that he had used for some experiments actually moved when the magnet was switched on, aligning itself at right angles to the magnetic field (this was the first time he used the term
When I spoke of this to Uncle Abe, he allowed me to experiment with the very powerful electromagnet he had in his attic, and I was able to duplicate a lot of Faraday’s findings, and to find, as he had, that the diamagnetic effect was especially powerful with bismuth, which was strongly repelled by both poles of the magnet. It was fascinating to see how a thin shard of bismuth (as near a needle as I could get with the brittle metal) aligned itself, almost violently, perpendicular to the magnetic field. I wondered whether, if it was sufficiently delicately poised, one might make a bismuth compass that pointed east-west. I experimented with bits of meat and fish, and wondered about experimenting with living creatures, too. Faraday himself had written, ‘If a man could be in the magnetic field, like Mahomet’s coffin he would turn until across the magnetic field.’ I wondered about putting a small frog, or perhaps an insect, in the field of Uncle Abe’s magnet, but feared this might freeze the motion of its blood, or blow its nervous system, turn out to be a refined form of murder. (I need not have worried: frogs have now been suspended for minutes in magnetic fields, and are apparently none the worse for the experience. With the vast magnets now available, an entire regiment could be suspended.)
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He was distracted, too, creatively, by a dozen competing interests and commitments during this time: the investigation of steels, the making of special highly refractive optical glasses, the liquefaction of gases (which he was the first to achieve), the discovery of benzene, his many chemical and other lectures at the Royal Institution, and the publication in 1827 of his