Lacaille’s grouping of
Norma, Circinus, and Triangulum Australe
Nicolas Louis de Lacaille depicted three
southern constellations as a group of draughtsman’s
instruments consisting of a set square and ruler
(l’Equerre et la Regle, now known as Norma), a pair of
compasses (Circinus), and a surveyor’s level (Triangulum
Australe). Norma and Circinus were Lacaille’s own
inventions but Triangulum Australe was an earlier invention of
Keyser and de Houtman which Lacaille adapted for the purpose.
The historian R. H. Allen mistakenly transferred the name
“niveau” (meaning level) from Lacaille’s
Triangulum Australe and applied it to Norma. This illustration
is from Jean Fortin’s Atlas
Céleste, a French version of
John Flamsteed’s Atlas
Coelestis. (Image © Ian
Ridpath.)
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