Lets talk Eyes!

               Thomas young as i have mentioned before was very interesting in understanding the eye. He had began taking measurements on the eye to better his understanding and amazingly his measurements were extremely similar to those of today's! He wanted to see how big of a distance there was from the back retina to the cornea and he got the measurement of 91 hundredth of an inch. He discovered this is an very painful way... He turned his eye ball inward as far as it could go, and slid a ring of one key in at the back of the eye and pressed on the back of the eyeball. That pressure produced a light showing he was close to the middle of the retina. He also measured the transverse diameter which he discovered was 98 hundredth of an inch.
To better understand this he came up with four hypothesis:

1. The curvature of the cornea changes.

2. The length of the eyeball changes

3. A combination of both occurs together.

4. Shape of the crystalline lens changes.

            To test the first hypothesis he submerged his eye in water. The unaided eye can not focus in water because the light passing through the water- cornea interface into the aqueous humor is no longer refracted because the aqueous humor which is very similar to water. Young decided to put a lens in front of the eye with a refractive power to eliminate air- cornea interface to allow the eye to focus again. Thus eliminating the first hypothesis.
For the second hypothesis Young used a method that would fix the length of the eyeball mechanically so it couldn't expand or contract, then he would focus on objects at different distances. When that didn't work he ruled out this hypothesis.
The third hypothesis was automatically ruled out due to the above.
However, this led Young to believe the fourth hypothesis was the correct one. But due to a change in mind, he wasn't so sure about it either.