Sentence:  If a is the major axis of an ellipsoid and b and c are the other two axes , the radius of curvature in the ab plane at the end of the <WSD>axis</WSD> is * * f , and the difference in pressure along the a and b axes is * * f . 
Meaning of the word marked with <WSD> tags:  a straight line through a body or figure that satisfies certain conditions