"The earth, says Prof. Balfour Stewart, FRS, - "is very seriously affected by what happens in the sun". . . a connection is strongly suspected "between epidemics and the appearance of the sun's surface". "One of the most famous plant epidemics is that of potato disease. The years 1846, 1860 and 1872 were bad years because of potato disease. Now these years are not very far from the years of maximum sunspot formation. [There is] a strange connection between these plant diseases and the state of the sun... The disease that appeared about three centuries ago, of a periodic and very violent character, called the "sweat sickness" ... appeared about the late fifteenth and early sixteenth centuries took place in the following years: 1485, 1506, 1517, 1528 and 1551, about eleven years between eruptions. Well, this is exactly the sunspot period... " The Sun and the Earth. Lecture by Prof. Balfour Stewart)."