Simply put, the eyeglass lens is a tool you use to focus light appropriately on your retina. For example, a lens that is concave, or curves inward, is used to correct nearsightedness, while a lens that is convex, or curves outward, is used to correct farsightedness.
Nearsightedness causes nearby objects to appear clear, while objects farther away look blurry. Farsightedness is where far away objects appear clear and objects up close appear blurry.
To correct astigmatism, which is caused by distortions in the shape of the cornea, a cylinder shaped lens is frequently used.
Whales and dolphins have a tool called echolocation, a sonar which allows them to "see" their prey, even it's internal workings! Noise pollution in the water has a significant effect on whales ability to navigate, hunt, locate their pods, and reproduce.
Echolocating animals have two ears positioned slightly apart. The echoes returning to the two ears arrive at different times and at different loudness levels, depending on the position of the object generating the echoes. The time and loudness differences are used by the animals to perceive direction. With echolocation the bat or other animal can see not only where it's going but can also see how big another animal is, what kind of animal it is, and other features as well. - wikipedia
Many modern submarines use their own sonar a low and mid-frequency sonar is so deafening the pressure waves affect animals on the cellular level, causing the equivalent of "the bends" or decompression sickness. For animals with echolocation this causes sonar function to fail and leaves these animals blind, if they're lucky. What often results is massive beachings (update: court blocks sonar 7/6/06)
The term "yard", was determined by King Henry I of England. The distance from his nose to the tip of his middle finger with arm extended became the standard "yard" measurement term.
The term, "taxicab", was formed from combining the word, taximeter and cabriolet. Taximeter is a tool for measuring time and distance and a cabriolet is a 2 wheeled 1 horse carriage.
