- Urania’s Mirror (ianridpath.com)
Urania’s Mirror is a boxed set of 32 constellation cards first published by Samuel Leigh of the Strand, London, in November 1824. An advertisement and review in the The London Literary Gazette for 1824 November 27 describes them as ‘fitted up in an elegant box’ and selling for £1 8s black and white or £1 14s ‘beautifully coloured’. They were described as ‘An acceptable present’ so no doubt the publication was timed to catch the Christmas market. The engraver was Sidney Hall but authorship was coyly attributed to ‘a lady’.
- Obtuse triangle (Wikipedia)
An obtuse triangle (or obtuse-angled triangle) is a triangle with one obtuse angle (greater than 90°) and two acute angles. Since a triangle’s angles must sum to 180° in Euclidean geometry, no Euclidean triangle can have more than one obtuse angle.
