Spheres of Air and Earth

Say “brilliant Italian inventor” and most people picture that shaggy fellow who, in between designing engines of war, painted enigmatic women and naked men. A rather better-groomed colleague of da Vinci’s, born some two hundred years later, went by the name of Francesco Lana de Terzi. His schemes for getting airborne were so far out that not even he believed in them, though to this day, among his other titles, he is styled a pioneer of aviation.

In 1670 this Jesuit from Brescia published a book called Prodromo (in full, Prodromo overo saggio di alcune inventioni nuove, premesso all’arte maestra – it was an age of titles longer than a lot of today’s videos, and just as full of themselves). Among other notions it sketches a flying ship shaped like an ordinary boat, sail and all. Just by way of a small refinement, four enormous copper spheres are fixed to it.

Naturally, the air was to be drawn out of these spheres. That the vacuum left inside would weigh less than the spheres’ original contents, we had suspected in theory as far back as antiquity. By the middle of the seventeenth century, though, it had been convincingly proved, and de Terzi was treating the vacuum as the hot novelty of the day. So hot that the work describing the Magdeburg mayor’s vacuum experiments came out a full two years after de Terzi’s Prodromo. Even so, it is on record that de Terzi knew of those experiments through mutual acquaintances and took his inspiration straight from them – which is why his designs, too, counted on copper, the metal Otto von Guericke had used in 1654.

The catch lay in the execution. For the spheres to be light enough to fly, they would have had to be so thin that the pressure outside would crumple them like an empty tin. Christiaan Huygens worked it out too, a few years on: he went over de Terzi’s design closely and concluded that the conflict between the strength required, the weight and the size of the spheres was “seemingly insurmountable”. And yet: swap the copper for cloth, the vacuum for hot air, and you have a balloon in your hands. So de Terzi almost hit on the principle that the Montgolfier brothers would use a hundred and thirteen years later in the marketplace at Annonay (hot air), and Jacques Charles two months after that on the Champ de Mars (hydrogen).

De Terzi never lived to see the true beginnings of aviation, of course – and more than that, he did not want to see them. He disowned his own designs on the grounds that they offended physics and, on top of that, God. It had struck him that a machine like this could easily be turned on cities from above, with no defence possible against it, and so would be pressed into war at once. Which is exactly what came to pass, as we now know. Not all of us, perhaps, recall that the first aerial bombardment in history was carried out by Austria – back then, my own country was part of it – when it laid siege to Venice in 1849 under Marshal Radetzky.

An inventor who hopes his invention will never work is a rare specimen (as a rule the brilliant mind charges after its project with tunnel vision, and if conscience catches up with it at all, it is only at the sight of the consequences, and then the man snivels quietly into his banknotes). And while de Terzi fretted over movement in the sky, something was quietly moving beneath his feet.

For the magnetic north pole is not nailed to the spot. The geographic pole, that imaginary tip of the Earth’s axis, stays put; the magnetic pole, the one the needle points to, roams. It is born of the swirling currents of molten iron deep in the Earth’s core, and those never stop turning over. Over the past few centuries it dawdled about the Canadian Arctic, then bolted out of nowhere across a whole ocean towards Siberia at some thirty miles a year – and lately it has slowed just as abruptly to twenty-two, the biggest slowdown ever measured.

No compass maker is celebrating a bump in sales over it; the update runs automatically in the user’s hand, and it need trouble nobody. Somebody has to keep an eye on these shifts all the same, and a great deal of paperwork comes of it. Aircraft and ships steer by magnetic north, and so every five years the so-called World Magnetic Model is brought up to date; load an outdated version for a long haul and you can miss your mark by a good ninety miles. And because airport runways are named for their magnetic heading, every so often they genuinely have to be renumbered and repainted. Somewhere out there someone takes up a brush and goes to put the world’s north right.

So much for the facts of our own world. What became of de Terzi, and where the north pole moved to in the world a step aside, you will find in the story The First Mechan.