The Human Eye
The human eye is the organ which gives us the sense of sight, allowing us to learn more about the surrounding world than we do with any of the other four sense. In order to understand how the human eye works, one must understand the anatomy of the eye. When you look at an object, light rays are reflected from the object to the cornea (a clear dome at the front of the eye), these rays are bent, refracted and focused by the cornea, lens and vitreous. The lens makes sure the rays come to sharp focus on the retina. When the image gets to the retina it is upside down. The light rays are then converted to electrical impulses which are then transmitted through the optic nerve, and to the brain where the image is translated and shown in an upright position. The amount of light entering the eye is controlled by the iris which lies in between the cornea and lens. Rays of light entering your eye are bent first by the curved transparent cornea, pass through the liquid aqueous humor and the hole through your muscular iris called the pupil, are further bent by the lens, and pass through your transparent vitreous humor before focusing on the rods and cons in the back of your eye. When it suddenly become dark, your gradual increase in sensitivity to the low level of light (dark adaptation) results from a shift from a predominantly cone vision to predominantly rod vision. In bright light, just one cone can stimulate a bipolar cell sufficiently to fire, providing greater visual acuity or resolution.
The colors of objects you see depend on the wavelengths of light reflected from those objects to your eyes. Light is the visible portion of the electromagnetic spectrum. When looking at ROYGBIV (red, orange, yellow, green, blue, indigo, violet) the colors vary in wavelength from the longest (red) to the shortest (violet). When light hits an object, different wavelengths of light can be reflected, transmitted, or absorbed. The more lightwaves your eyes receive (the higher the amplitude of the wave), the brighter an object appears. The wavelengths of light that reach your eye from the object determine the color, or hue, the object appears to be.
Vision is tested by reading a Snellen eye chart at a distance of 20 feet. By looking at lots of people, eye doctors have decided what a “normal” human being should be able to see when standing here. If you have 20/20 vision, it means that when you stand 20 feet away from the chart you can see what a “normal” person can see. If you have 20/40 vision, it means that when you stand 20 feet away from the chart, you can only see what a normal human can see when standing 40 feet from the chart.
There are many different types of vision problems. Some of the more common problems are the following:
Amblyopia, Strabismus:This occurs when one eye turns in or out, up or down, or there is a lazy eye. In this condition you may see double or print may run together.
General Binocular Problems:When the two eyes fail to work together, eye strain and fatigue can occur. If left untreated, reduced comprehension or avoidance of reading are commonly found.
Visual Perceptual Dysfunction:This occurs when eye-hand coordination, visual memory, reversals, and other visual perceptual areas are deficient or undeveloped. This results in decreased efficiency in the development of learning.
Inappropriate Visual Development:When visual skills of infants are not developing appropriately, strabismus and other visual conditions may occur. If treated immediately, the prognosis is excellent.
Closed Head Trauma Syndrome:
As a result of a head injury, visual skills may be lost or deficient. Often double vision, disorientation and other visual problems result, which should be treated as soon as possible.
sorry this is so late mr.wirth, i kept having problems with uploading the pictures but i finally figured out how to get it to work!
The Wimshurst machine is an electrostatic device used to generate high voltages between 1880 and 1883 by British inventor James Wimshurst. In this machine, the two insulated disks and their metal sectors rotate in opposite directions passing the crossed metal neutralizer bars and their brushes. An imbalance of charges is then induced, amplified and collected by two pairs of metal combs with points placed near the surfaces of each disk. These collectors are mounted on insulating supports and connected to the output terminals. The positive feedback increases the charges exponentially until the dielectric breakdown voltage of the air is reached and a spark jumps across the gap. 
