On Little Earths and Little Suns

Terrella and Solellus

Reading the English translation of William Gilbert’s (1544-1603) De Magnete (On the Magnet¹), I came across an interesting term: the terrella, which means little Terra, i.e., little Earth. Gilbert explains how to create a terrella:

But since the spherical form, which is also the most perfect, agrees best with the earth, being a globe, and is most suitable for use and experiment, we accordingly with our principal demonstrations by the stone to be made with a globe-shaped magnet as being more perfect and adapted for the purpose. Take then, a powerful loadstone, of a just size, uniform, hard, without flaw; make of it a globe upon the turning tool used for rounding crystals and some other stones, or with other tools as the material and firmness of the stone requires, for sometimes it is difficult to be worked. The stone thus prepared is a true, homogeneous offspring of the earth and of the same shape with it: artificially possessed of the orbicular form which nature granted from the beginning to the common mother earth: and it is a physical corpuscle imbued with many virtues, by means of which many abstruse and neglected truths in philosophy buried in piteous darkness may more readily become known to men.  This round stone is called by us a μιχρόγη [michroge] or Terrella. [pp.12-13]

Many of the experiments Gilbert described in his De Magnete use this terrella:

William Gilbert’s terrella

The term terrella was revived some three centuries later by the Norwegian scientist and engineer Kristian Birkeland (1867-1917), who studied the aurora borealis by making a trip to Nordkapp in northern Norway in the middle of the winter for detailed observations and by undertaking experiments with a terrella in his laboratory. He ultimately concluded that the aurorae are the result of electrical currents connecting the Earth and the Sun. We now call these currents Birkeland currents. Here is Birkeland in his laboratory, with his terrella:

Kristian Birkeland’s terrella

What about Little Suns?

More recently, the Safire Project² undertook a series of experiments to simulate the sun, in order to verify the Electric Sun model first proposed by Ralph Juergens (1924-1979). These experiments, reminiscent of those of Birkeland, involve subjecting an anode to a variety of electrical currents and making detailed observations. So how should we call a little sun?

Looking in the Französisches Etymologisches Wörterbuch, under the entry sol³, we find three possibilities: soliculus, soluculus and solellus. The latter term, solellus, is the etymological root of the French word for sun, soleil. The term is composed of three syllables, like terrella. So this would give us:

• a small Terra (Earth) is a terrella, plural terrellae;

• a small Sol (Sun) is a solellus, plural solelli.

My next project will be to write about De Magnete.

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1. William Gilbert, On the Magnet, London: Chiswick Press, 1900. Translation of De Magnete, first published in 1600.

2. Safire Project. https://www.safireproject.com.

3. Französisches Etymologisches Wörterbuch. Founded by Walther von Wartburg. Entry sol. https://lecteur-few.atilf.fr/lire/120/30.