284 GENERAL SCIENCE 



(b) Farsightedness is caused by the eyeball being too 

 short from the front to the back or by the crystalline 

 lens not being sufficiently convex to bring the light to 

 a focus on the retina. The light is not focused soon enough 

 to see objects that are near. The person thus affected 

 can often see distant objects better than a person with a 

 normal eye, and usually holds a paper at arm's length 

 when he reads. Farsightedness is a very common defect 

 among people after they pass the age of fifty years. With 

 young people it is rare. The remedy is to wear glasses 

 with converging lenses. 



(c) Color Blindness. Men as a rule are not as much 

 interested in the various shades of color as are women, 

 and so they are not able to distinguish colors so readily, 

 that is, to call them by name. This does not mean that 

 men are unable to distinguish a difference between two 

 shades of color, but that they may be unable to name the 

 difference or even to name the colors under consideration. 

 This is due to a lack of knowledge on the part of men and 

 not to a defect of the eye. 



Color blindness is a defect of the eye which makes it 

 unable to distinguish any difference between certain colors. 

 Red and green with their various shades are the colors 

 which color-blind persons are unable to recognize. Their 

 eyes do not respond to the ether waves that produce the 

 sensation of red and green in the normal eye. The cause 

 of the defect is not known and so cannot be remedied. 

 Some investigators say that one out of every twenty male 

 persons is color blind, while only one out of every two 

 hundred females has the same defect. Red and green 

 lights are the danger and safety signals used by the rail- 

 roads and navigation companies, therefore it is very 

 important for engineers and pilots not to be color blind, 



