The twine fits exactly. On the basis of these measurements, she concludes that the area of the room is 15.17 m 2 . Pencil marks do not move about on walls. A string pulled taut twice will be the same length on both occasions. The area of a four-sided room, whose opposite sides are equal and whose diagonals are equal, may be determined by multiplying its width by its length.
Lengths add like numbers.
The order in which the measurements are taken is irrelevant, i.e. would be the same if they had been taken in the reverse order. The walls are not bowed. Etc., etc., etc. It was common knowledge in Jenner's time that a person could catch smallpox only once. Many people tried to inoculate themselves with matter from smallpox sores.