9781422277638

A London street scene during the Great Plague. Houses “visited” by the Plague were marked by a cross, and char- coal, pitch and brimstone were burned outside in the hope that this would kill it off.

Words to Understand

alchemy— the art and science that aimed at the “perfection” of matter through chemical operations understood in religious terms. The alchemist who could turn a base metal into gold was also supposed to have attained religious self-perfection. apothecary— the ancestor of our druggist or pharmaceutical chemist. He prepared and sold drugs for medicinal purposes. calculus— the mathematical method used to calculate the rate of change of continuously varying quantities by treating the infinitesimal differences between consecutive values of such quantities. There are two forms of calculus, differential and integral. gravitation— Newton’s Law of Universal Gravitation states that every particle of matter in the universe attracts every other with a force that varies directly as their masses and inversely as the square of the distance between them.