The A B C of atoms

by Bertrand Russell

, has made the top of the hoop sink to

. The hoop is supposed to be fastened, like a wheel, on to an axle in the middle,

. An ellipse can be obtained from a circle which is standing upright by diminishing all vertical distances in a certain fixed proportion; that is to say, if

is any point of the circle, which is at a height

above the level of the axle, we go down to a point