Note 268 — CANTO THE FOURTH.
Reading edition
{216}[The cyanometer, an instrument for ascertaining the intensity of the blue colour of the sky, was invented by Horace Bénédict de Saussure (1740-1799); see his Essai sur l'Hygrométrie. F.H. Alexander von Humboldt (1769-1859) "made great use of his instrument on his voyages, and ascertained by the colour the degree of blueness, the accumulation and the nature of the non-transparent exhalations of the air."—Alexander von Humboldt, by Professor Klencke, translated by Juliette Bauer, 1852, pp. 45, 46.]