1893 text

Professor Silvanus P. Thompson, F.R.S., has kindly supplied me with the following interesting note on the terrella (or terella): The name given by Dr. William Gilbert, author of the famous treatise, “De Magnete” (Lond. 1600), to a spherical loadstone, on account of its acting as a model, magnetically, of the earth; compass-needles pointing to its. poles, as mariners’ compasses do to the poles of the earth. The term was adopted by other writers who followed Gilbert, as the following passage from Wm. Barlowe’s “Magneticall Advertisements” (Lond. 1616) shows: “Wherefore the round Loadstone is significantly termed by Doct. Gilbert Terrella, that is, a little, or rather a very little Earth: For it representeth in an exceeding small model (as it were) the admirable properties magneticall of the huge Globe of the earth” (op. cit, p. 55). Gilbert set great store by his invention of the terrella, since it led him to propound the true theory of the mariners’ compass. In his portrait of himself which he had painted for the University of Oxford he was represented as holding in his hand a globe inscribed terella. In the Galileo Museum in Florence there is a terrella twenty-seven inches in diameter, of loadstone from Elba, constructed for Cosmo de’ Medici. A smaller one contrived by Sir Christopher Wren was long preserved in the museum of the Royal Society (Grew’s “Rarities belonging to the Royal Society,” p. 364). Evelyn was shown “a pretty terrella described with all ye circles and skewing all y magnetic deviations” (Diary, July 3rd, 1655).

This text comes from a footnote on a diary entry in the 1893 edition edited by Henry B. Wheatley.

6 Annotations

TerryF  •  Link

Terrella in the Wikipedia

William Gilbert’s ‘Terrella’

William Gilbert (or Gilberd, as he wrote it…)

William Gilbert aka William of Colchester "set out to debunk magical notions of magnetism, yet in building an intellectual bridge between natural philosophy and emerging sciences, he did not completely abandon reference to the occult. For example, he believed that an invisible ‘orb of virtue’ [force] surrounds a magnet and extends in all directions around it. Other magnets and pieces of iron react to this orb of virtue and move or rotate in response. Magnets within the orb are attracted whereas those outside are unaffected. The source of the orb remained a mystery. Although his language was that of the natural philosophy of the time, some of his ideas were ahead of his time. His orbs of virtue were a fledgling notion of the idea of fields that would revolutionize physics more than two centuries later."

in aqua  •  Link

Exposure to Sam on his first visit to this august group, but mentioned by John Evelyn.Wednesday 23 January 1660/61
"With [Greatorex] to Gresham Colledge (where I never was before), and saw the manner of the house, and found great company of persons of honour there"
:[jan 1661 J Evelyn ]23. To Lond, at our Society, where was divers Exp: on the Terrella sent us by his Majestie

RennyBA  •  Link

I think you have an very interesting article of the phenomena Terrella her and as a Norwegian of course I know about Birkeland's Terella.
I'm a blogger and write about Norway, our cultures, traditions and habits and call it my Terella. My little earth or the world seen trough my eyes if you like.

Terry Foreman  •  Link

Two terrellae

A terrella (‘little earth’) is a sphere made of a magnetized substance, used to simulate the magnetic field of the earth. In the 16th century the English physician William Gilbert used a terrella made out of lodestone (a naturally-occurring magnetized mineral) to demonstrate that the earth is magnetic, and to explain how mariners’ compasses work. The Society used several terrellae in experimental demonstrations at meetings in the 17th century. Sir Christopher Wren donated one that was the same size as the larger of these two examples (bottom image). http://royalsociety.org/exhibitions/350years/tw...

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Chart showing the number of references in each month of the diary’s entries.