the cyanometer

In the late 1700s, Swiss scientist Horace-Bénédict de Saussure made a tool to measure the blueness of the sky. Saussure climbed mountains regularly and noted that the color of the sky changed with elevation and became “more blue.” His theory was that the color indicated the moisture content of the sky, and to test the idea, he set his sights on climbing Mont Blanc, the highest peak in Western Europe. He brought swatches of blue and held them up to the sky to compare the gradations of color until...