When bats fly they produce ultrasonic sound waves which are reflected back to them from the obstacles in their way and hence they can fly without difficulty.
Coins were first made in the seventh century B.C.E. in Lydia, Asia Minor (presentday Turkey). They were issued by the early Lydian kings—probably Alyattes or Sadyattes— about 600 B.C.E., several decades before the reign of the famous Lydian king Croesus. Lydian coins were made out of electrum, a mixture of gold and silver, and each was weighed and stamped with a lion’s head, the king’s symbol. About 0.03 pounds (14 grams) of electrum was one stater (meaning “standard”). A stater was about one month’s pay for a soldier. Today’s coins are not made from precious metals like gold and silver, but from inexpensive alloys such as cupro-nickel, which is a combination of copper and nickel. Unlike early coins, the metal in today’s coins is worth far less than its value in the marketplace.
Bulbs, corms, and tubers are all parts of a plant that grow underground. They are each a storage unit for food that gives the plant the energy it needs to grow, bloom, and complete its life cycle each year. A bulb is an underground stem and leaf. It grows in protective layers, much like an onion. At the very center of the bulb is a small version of the flower itself. The bulb’s basil plate—a round and flat hairy mass (the beginnings of roots) on the bottom of the bulb—helps the bulb stay together. Examples of bulbs include tulips, daffodils, lilies, narcissus, and amaryllis. A corm is an underground stem. It has the same type of protective covering and basal plate as the bulb, but it does not grow in layers. Instead, the corm is the base for the flower stem and has a solid texture. Crocuses and gladiolus are both corms. The tuber is an underground stem or root. Just like a potato, it has leathery skin, lots of “eyes,” and no basal plate. The eyes are the growing points where the plants eventually emerge. Dahlias, begonias, and anemones are all tubers.
The hard pavement surface we now call asphalt was discovered by chance when an Englishman named E. Purnell Hooley accidentally spilled tar onto some crushed stone. Hooley named this new black pavement by taking the last name of Scotsman John MacAdam, who had developed the use of crushed stone for a firm, dry highway, and prefixing it with “tar.” Tarmacadam was a mouthful, however, and was soon shortened to Tarmac. Hooley patented Tarmac in 1903.
Measures refractive indices
Each year, about 150,000 children are treated in emergency rooms for head injuries that occurred while riding their bikes. Many bike-related injuries could be avoided if riders wore their helmets properly. Wearing a bike helmet reduces the risk of brain injury by as much as 88 percent and reduces the risk of injury to the face by 65 percent. That is why many state laws say that bicyclists under the age of 14 are required to wear approved bicycle helmets when they ride their bicycles. If your friends don’t wear helmets when you bicycle together, teach them by your wise example. In the United States, bicycle helmets save one life every day and prevent one head injury from happening every four minutes.
A horseshoe’s charm comes from the legend of Saint Dunstan, who, because of his talent as a blacksmith, was asked by the Devil to shoe his cloven hoof. Saint Dunstan agreed, but in carrying out the task, he caused the Devil such pain that he was able to make him promise never to enter a house that has a horseshoe hanging above the doorway. Thus, from the Middle Ages on, the horseshoe has been considered good luck.
Although there are other windy planets (like Uranus), Neptune’s winds are the fastest in the solar system, reaching 1,600 miles (2,575 kilometers) per hour. Nep- 8 tune’s large, sweeping wind storms could consume the entire planet Earth!
The walrus’s two tusks—which are really two long, sharp teeth—aid the cold-water creature in battling polar bears, fending off other walruses, and walking around the bottom of the ocean while searching for its favorite food, clams. The “tooth walker” temporarily anchors itself to the bottom of the ocean by pushing its tusks into the muddy sand, where it can look for food. It then pulls its tusks out, moves on, and repeats the process.
In the seventeenth century, the British borrowed a Dutch army custom of sounding a drum and bugle to signal soldiers that it was time to stop socializing and return to their barracks for the night. The Dutch called it “taptoe,” meaning “shut off the taps,” and the abbreviated “taps” became a signal for tavern owners to turn off the spigots on their beer and wine casks.
After lights out, taps signals that the soldiers are safely home, which is why it’s played at funerals.