Then the observer at the point A will continue to receive the reflected rays of the sun until that body reaches the point S, which is, according to the hypothesis, nineteen degrees below the horizon line of the observer at A.This horizon line, being represented by AH, and the sun's ray by SM, the angle HMS is an angle of nineteen degrees.

The complementary angle SMA is, obviously, an angle of (180-19) one hundred and sixty-one degrees.
But since M is the reflecting surface and the angle of incidence equals the angle of reflection, the angle AMC is an angle of one-half of one hundred and sixty-one degrees, or eighty degrees and thirty minutes.
Now this angle AMC, being known, the right-angled triangle MAC is easily resolved, since the side AC of that triangle, being the radius of the earth, is a known dimension.

Resolution of this triangle gives us the length of the hypotenuse MC, and the difference between this and the radius (AC), or CD, is obviously the height of the atmosphere (h), which was the measurement desired.

According to the calculation of Alhazen, this h, or the height of the atmosphere, represents from twenty to thirty miles.

The modern computation extends this to about fifty miles.
But, considering the various ambiguities that necessarily attended the experiment, the result was a remarkably close approximation to the truth.
Turning from physics to chemistry, we find as perhaps the greatest Arabian name that of Geber, who taught in the College of Seville in the first half of the eighth century.