Background Informations:
On June 1, 2008, China National Philatelic Corporation issued a first-day cover "Cao Chong Weights the Elephant", carrying one set of two special stamps with a total face value of 2.40 yuan. The pictures on the stamps are "Marking the Water Level on Boat Loaded with Elephant" and "Replacing the Elephant with Weighable Objects".
"Cao Chong Weights the Elephant", a historical tale widely circulated among the folk people, is about child prodigy Cao Chong, who applied the principle of buoyancy to measure the accurate weight of an elephant. According to the story, during the Three Kingdoms Period(220-280), Sun Quan, of the Kingdom of Wu, presented an elephant as a gift to Cao Cao, of the Kingdom of Wei. Cao Cao wished to know the animal's weight, but none of his ministers could come up with a method. Then, Cao Chong, at the age of six, stood out. He asked to have the elephant loaded onto a boat and mark the water level. The elephant was the replaced with smaller weighable stones until the boat was submerged to the marked level. The weight of the elephant could then be found out by summing up the weights of all the stones. The child's superior wisdom has since been widely acclaimed.
