Minor axis — where it appears
Named by 2 essays across 2 fields — each of them below, with the objects they name alongside it.
The circle whose centre moves
The image of a circle is an ellipse, and the image of the circle's centre is not the centre of that ellipse. The gap is 3 or 4% of the ellipse's width in an ordinary view — large enough to see, small enough to be dismissed as a slip by anyone not expecting it, and the reason drawn wheels look wrong.
Which way the drawn circle leans
Two rules are given for the direction a drawn circle's short axis runs in: along the axis of the cylinder, and pointing at the centre of vision. On the optical axis both are exactly right. At the edge of an ordinary frame the first is out by three and a half degrees and the second by seventy-nine. The statement neither of them is comes out of differencing the projection, and it matches the drawn ellipse to a hundredth of a degree.
Named alongside it
The objects these essays reach for when they reach for this one.
ConicForeshorteningConic fittingDrawing officeEllipseEllipse fitHorizonJacobianline at infinityMidpointPicture planepole and polar