Pocket Forecaster, Negretti & Zambra, c.1915; Julie Johnstone, sky viewing permit, 2017; Julie Johnstone, cyanometer, after Horace-Bénédict de Saussure, 1-100%, 2017. Photo: Julie Johnstone
cyanometer permit
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Pocket Forecaster, Negretti & Zambra, c.1915; Julie Johnstone, sky viewing permit, 2017; Julie Johnstone, cyanometer, after Horace-Bénédict de Saussure, 1-100%, 2017. Photo: Julie Johnstone