ATDTDA (1): De Forest and Kimura (29:32-3)

[Ya Sam]

See also

In the Annals of Mathematics [...] a Japanese scholar, Dr. Shunkichi Kimura, 
published a paper on the nabla of quaternions. The word was not unknown to 
English and American scholars at that time, but it seems never to have been 
generally accepted in the mathematical vocabulary, at least in this country. 
[...]

from an address given by Lord Kelvin

‘I took the liberty of asking Professor Ball two days ago whether he had a 
name for this symbol*; and he mentioned to me nabla, a humorous suggestion 
of Maxwell’s. It is the name of an Egyptian harp which was of that shape. I 
do not know that it is a bad name for it.’

The word is found in various languages, as seen in the Latin nabla, nablu, 
or nablium, a synonym for psalterium, a psalter or harp.

* This was a quaternion symbol, a right triangle with the vertex of an acute 
angle pointing downward and an exponent 2 at the right.

p. 304

Scripta Mathematica
Jekuthiel Ginsburg

http://www.amazon.com/Scripta-Mathematica-Jekuthiel-Ginsburg/dp/0766138356/sr=1-3/qid=1170255316/ref=sr_1_3/102-4310607-9589700?ie=UTF8&s=books

Nabla is a symbol, shown as . The name comes from the Greek word for a 
Hebrew harp with a similar shape. Related words also exist in Aramaic and 
Hebrew. The symbol was first used by William Rowan Hamilton in the form of a 
sideways wedge: ⊳ [1]. Another, less-common name for the symbol is 
atled (delta spelled backwards) because the nabla is an inverted delta. [1]

http://en.wikipedia.org/wiki/Nabla_symbol

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