Answer to Question 1
A telescope, mounted on a table tangential and perpendicular to Earth's center, is sighted on the North Star. This star is nearly directly above our rotational axis. The angle between the line drawn to the North Star and the line to the center of Earth determines latitude. However, this only works when Earth is uniform and the surface smooth. Large masses of rock pull the plumb bob towards them and away from the center of Earth, causing error, although calculated error was much greater than the observed error. Pratt proposed that the deflection is consistent with observations because the crust below the mountains is of lower density. Airy suggested that the crust was more dense than expected, providing a root below the mountain.
Answer to Question 2
c. 50
Milking reindeer in the 19th century
A set of tie stalls in an 18th century stable
Frequent errors in nursing interventions
Average Global Temperature Rise over the Past Century
Wang Guochen, c. nineteenth century
Formation of the Himalayas