The distance along the horizontal line-or the abscissa, as a mathematician would call it-represents the date.
"The Story of the Heavens"
Robert Stawell Ball
The curve as a whole becomes, first slightly convex to the abscissa, then straight and ascending, and lastly concave.
"Response in the Living and Non-Living"
Jagadis Chunder Bose
In the figure it will be noticed that the rising portion of the curve is somewhat steep, and the recovery convex to the abscissa, the fall being relatively rapid in its first, and less rapid in its later, parts.
"Response in the Living and Non-Living"
Jagadis Chunder Bose