Uncle Tungsten

14. Lines of Force

When I was very young I had been intrigued by ‘frictional’ electricity, of the sort that made rubbed amber attract bits of paper, and when I returned from Braefield, I began to read about ‘electrical machines’ – discs or globes of some nonconducting material, turned by a crank and rubbed against the hand, or a cloth, or a cushion of some sort – which would produce powerful sparks or shocks of static electricity. It seemed easy enough to make such a simple machine, and in my first attempt at making one I used an old record as the disc. Gramophone records at the time were made of vulcanite and easily electrified; the only problem was that they were thin and fragile, easily shattered. For a second, more robust machine, I used a thick glass plate and a cushion covered with leather and coated with zinc amalgam. I could get handsome sparks from this, more than an inch long, if the weather was dry. (Nothing worked if the weather was damp, for then everything conducted.)

One could connect the electrical machine to a Leyden jar – basically a glass jar coated with tinfoil on both sides, and a metal ball at the top, connected to the inside foil by a metal chain. If one connected several such jars together, they could hold a formidable charge. It was such a ‘battery’ of Leyden jars in the eighteenth century, I read, which had been used in one experiment to give an almost paralyzing shock to a line of eight hundred soldiers, all of them joined by holding hands.

I also got a small Wimshurst machine, a beautiful thing with revolving glass discs and radiating metal sectors that could yield massive sparks up to four inches long. When the plates of the Wimshurst machine were revolving fast, everything around it became highly charged: tassels became electrified, their threads straining apart; pithballs would fly apart, and one felt the electricity on one’s skin. If there was a sharp point nearby, electricity would stream from it in a luminous brush, a little corposant, and one could blow out candles with the outstreaming ‘electric wind’, or even get this to turn a little rotor on its pivot. Using a simple insulating stool – a wooden board supported by four tumblers – I was able to electrify my brothers so their hair stood on end. These experiments showed the repulsive power of like electric charges, each thread of the tassel, each hair, acquiring the same charge (whereas my first experience, with rubbed amber and bits of paper, had shown the power of electrically charged bodies to attract). Opposites attracted, likes repelled.

I wondered whether one could use the static electricity of the Wimshurst machine to light up one of Uncle Dave’s lightbulbs. Uncle said nothing, but provided me with some very fine wire made of silver and gold only a three-hundredth of an inch thick. When I connected the brass balls of the Wimshurst machine with a three-inch length of silver wire on a card, the wire exploded when I turned the handle, leaving a strange pattern on the card. And when I tried it with the gold wire, this was vaporized instantly, turning into a red vapor, gaseous gold. It seemed to me from these experiments that frictional electricity could be quite formidable – but that it was too violent, too intractable, to be of much use.

Electrochemical attraction, for Davy, was the attraction of opposites – the attraction, for example, of an intensely ‘positive’ metallic ion, a cation like that of sodium, to an intensely ‘negative’ one, an anion like that of chloride. But most elements, he thought, came between these on a continuous scale of electro-positivity or -negativity. The degree of electro-positivity among metals went with their chemical reactivity, hence their ability to reduce or replace less positive elements.

This sort of replacement, without any clear notion of its rationale, had been explored by the alchemists in the production of metallic coatings or ‘trees.’ Such trees were made by inserting a stick of zinc, say, into a solution of another metallic salt (a silver salt, for example). This would result in the displacement of the silver by the zinc, and metallic silver would be precipitated from the solution as a shining, almost fractal, arborescent growth. (The alchemists had given these trees mythical names, so the silver tree was called Arbor Dianae, the lead tree Arbor Saturni, and the tin tree Arbor Jovis.)[34]

I had hoped, at one point, to make such trees of all the metallic elements – trees of iron and cobalt, and bismuth and nickel, of gold, of platinium, of all the platinium metals; of chromium and molybdenum, and (of course!) tungsten; but various considerations (not least, the prohibitive cost of the precious metal salts) confined me to a dozen or so basic ones. But the sheer aesthetic delight of these – no two trees ever looked the same; they were as different, even with the same metal, as snowflakes or ice crystals, and different metals, one could see, were deposited in different ways – soon gave way to a more systematic study. When did one metal lead to the deposition of another? And why? I used a zinc rod, sticking it first into a solution of copper sulfate, and got a gorgeous encrustation, a copper plating, all around it. I then experimented with tin salts, lead salts, and silver salts, putting a zinc rod into solutions of these, and produced shining, crystalline trees of tin, lead, and silver. But when I tried to make a zinc tree, by sticking a copper rod into a solution of zinc sulphate, nothing happened. Zinc was clearly the more active metal, and as such could replace the copper, but not be replaced by it. To make a zinc tree, one had to use a metal even more active than zinc – a magnesium rod, I found, worked well. Clearly all these metals did form a sort of series.

Davy himself pioneered the use of electrochemical displacement for protecting the copper bottoms of ships from corrosion in seawater, attaching to them plates of more electropositive metals (such as iron or zinc), so that these would become corroded instead, a so-called cathodic protection. (Though this seemed to work well under laboratory conditions, it did not work well at sea, because the new metal plates attracted barnacles – and thus Davy’s suggestion was ridiculed. Yet the principle of cathodic protection was brilliant, and eventually became, after his death, a standard way of protecting the bottoms of ocean-going vessels.)

Reading about Davy and his experiments stimulated me to a variety of other electrochemical experiments: I put an iron nail in water, attaching a piece of zinc to it to protect it from corrosion. I removed the tarnish from my mother’s silver spoons by putting them in an aluminium dish with a warm solution of sodium bicarbonate. She was so pleased by this that I decided to go further and try electroplating, using chromium as the anode and a variety of household objects as the cathode. I chromium-plated everything I could lay hands on – iron nails, bits of copper, scissors, and (this time to my mother’s considerable annoyance) one of the silver spoons that I had previously cleaned of tarnish.

I did not realize at first that there was any connection between these experiments and the batteries I was playing with at the same time, although I thought it an odd coincidence that the first pair of metals I used, zinc and copper, could produce either a tree or, in a battery, an electric current. I think it was only when I read that, to get a higher voltage, batteries used nobler metals such as silver and platinum that I started to realize that the two series – the ‘tree’ series and Volta’s series – were probably the same, that chemical activity and electrical potential were in some sense the same phenomenon.

We had a large old-fashioned battery, a wet cell, in the kitchen, hooked up to an electric bell. The bell was too complicated to understand at first, and the battery, to my mind, was more immediately attractive, for it contained an earthenware tube with a massive, gleaming copper cylinder in the middle, immersed in a bluish liquid; all this inside an outer glass casing, also filled with fluid, and containing a slimmer bar of zinc. It looked like a miniature chemical factory of sorts, and I thought I saw little bubbles of gas, at times, coming off the zinc. This Daniell cell (as it was called) had a thoroughly nineteenth-century, Victorian look about it, and this extraordinary object was making electricity all by itself – not by rubbing or friction, but just by virtue of its own chemical reactions. That this was quite another source of electricity, not frictional or static, but a radically different sort of electricity, must have seemed astounding in the extreme, a new force of nature, when Volta discovered it in 1800. Previously there had been only the fugitive discharges, the sparks and flashes, of frictional electricity; now one could have at one’s disposal a steady, uniform, unvarying current. One only needed two different metals – copper and zinc would do, or copper and silver (Volta worked out a whole series of metals, differing in the ‘voltage’, the potential difference, between them), immersed in a conducting medium.

The first batteries I made myself used fruit or vegetables – one could stick copper and zinc electrodes into a potato or a lemon and get enough current to light a tiny 1-volt bulb. And one could wire half a dozen lemons or potatoes together (in series to get a higher voltage, or in parallel to get more power) to make a biological ‘battery.’ After the fruit and vegetable batteries, I turned to coins, using alternating copper and silver coins (one had to use silver coins made before 1920, for later ones were debased) with moistened (usually saliva-moistened) blotting paper between them. If I used small coins, farthings and sixpences, I could get five or six such couples in an inch, or I could make a pile a foot high, with sixty or seventy couples, enclosed in a tube, which could give quite a sharp, 100-volt shock. One could go on, I thought, to make an electric stick filled with narrow couples of copper and zinc foil, a lot thinner than coins. Such a stick, with five hundred or more couples, might generate a thousand volts, more even than an electric eel, enough to frighten off any assailant – but I never got as far as making one.

I was fascinated by the huge range of batteries developed in the nineteenth century, some of which I could see in the Science Museum. There were ‘single fluid’ batteries, like Volta’s original cell, or the Smee, or the Grenet, or the massive Leclanche, or the slim, silver battery of de la Rue; and there were two-fluid batteries, like our own Daniell, and the Bunsen, and the Grove (which used platinum electrodes). Their number seemed endless, but all were designed, in their different ways, to secure a more reliable and constant flow of current, to protect the electrodes from the deposition of metal or the adherence of gas bubbles, and to avoid (as some batteries caused) the emission of noxious or inflammable gases.

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 1820^s.

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 1880^s, 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.)

Like Faraday, I started to see ‘lines of force’ everywhere. I already had battery-powered front and rear lamps on my bike, and now I got dynamo-powered lights as well. As the little dynamo whirred on the back wheel, I would think sometimes of the magnetic lines of force being cut as it whirred, and of the mysterious, crucial role of motion.

Magnetism and electricity had seemed at first completely separate; now they seemed to be linked, somehow, by motion. It was at this point that I turned to my ‘physics’ uncle, Uncle Abe, who explained that the relationship between electricity and magnetism (and the relationship of both to light) had indeed been made clear by the great Scottish physicist Clerk Maxwell.[37] A moving electrical field would induce a magnetic field near it, and this in turn would induce a second electrical field, and this another magnetic field, and so on. With these almost instantaneous mutual inductions, Maxwell envisaged, there would be, in effect, a combined electromagnetic field in extremely rapid oscillation, and this would expand in all directions, propagating itself as a wave motion through space. In 1865, Maxwell was able to calculate that such fields would propagate at 300,000 kilometers per second, a velocity extremely close to that of light. This was very startling – no one had suspected any relationship between magnetism and light; indeed, no one had any idea what light might be, although it was well understood that it was propagated as a wave. Now Maxwell suggested that light and magnetism were ‘affections of the same substance, and that light is an electromagnetic disturbance propagated through the field according to electromagnetic laws.’ After hearing this, I began to think of light differently – as electric and magnetic fields leapfrogging over each other with lightning speed, braiding themselves together to form a ray of light.

It followed, as a corollary, that any varying electric or magnetic field could give rise to an electromagnetic wave propagating in all directions. It was this, Abe said, that inspired Heinrich Hertz to look for other electromagnetic waves – waves, perhaps, with a much longer wavelength than visible light. He was able to do this, in 1886, by using a simple induction coil as a ‘transmitter’ and small coils of wire with tiny (a hundredth of a millimeter) spark gaps as ‘receivers.’

When the induction coil was set to sparking, he could observe, in the darkness of his lab, tiny secondary sparks in the small coils. ‘You switch on the wireless’, said Abe, ‘and you never think of the wonder of what’s actually happening. Think how it must have seemed on that day in 1886 when Hertz saw these sparks in the darkness and realized that Maxwell was right, and that something like light, an electromagnetic wave, was raying out from his induction coil in every direction.’

Hertz died as a very young man, and never knew that his discovery was to revolutionize the world. Uncle Abe himself was only eighteen when Marconi first transmitted radio signals across the English Channel, and he remembered the excitement of this, even greater than the excitement over the discovery of X-rays two years earlier. Radio signals could be picked up by certain crystals, especially crystals of galena; one would have to find the right spot on their surface by exploring them with a tungsten wire, a ‘cat’s whisker.’ One of Uncle Abe’s own early inventions was to make a synthetic crystal that worked even better than galena. Everyone still spoke of radio waves as ‘Hertzian waves’ at this point, and Abe had called his crystal Hertzite.

But the supreme achievement of Maxwell was to draw all electromagnetic theory together, to formalize it, to compress it, into just four equations. In this half-page of symbols, Abe said, showing the equations to me in one of his books, was condensed the whole of Maxwell’s theory – for those who could understand them. Maxwell’s equations revealed, for Hertz, the lineaments of ‘a new physics… like an enchanted fairyland’ – not only the possibility of generating radio waves, but a sense that the whole universe was crisscrossed by electromagnetic fields of every sort, reaching to the ends of the universe.