# Earliest Known Uses of Some of the Words of Mathematics (X)

**X-AXIS.**

*Axis of x*appears in "On the Attractions of Homogeneous Ellipsoids" by James Ivory,

*Philosophical Transactions of the Royal Society of London,*Vol. 99. (1809), pp. 345-372. [JSTOR].

*Axis of abscissas*and

*axis of ordinates*are found in 1850 in

*The elements of analytical geometry*by John Radford Young: "The distance,

*AB*, is denominated the abscissa of the point;

*P*, and

*BP*, or its equal,

*AC*, is called the ordinate of the same point; hence the axis

*AX*is distinguished from the axis

*AY*by the name axis of abscissas, the latter being called axis of ordinates. The abscissa and ordinate of a point, when spoken of together, are, for the sake of brevity, called the coordinates of the point, and, for a like reason, the two axes are referred to as axes of coordinates. An abscissa is generally denoted by the letter

*x*, and an ordinate by the letter

*y*; and often, for shortness, the axis of abscissas is called the axis of

*x*, and the axis of ordinates the axis of

*y*." [University of Michigan Digital Library]

*X-axis*is found in 1852 in

*Acoustics*by W. F. Donkin [Google print search].

The terms

**X-COORDINATE, Y-COORDINATE,**and

**Z-COORDINATE**appear in a paper published by James Joseph Sylvester in 1863 [James A. Landau].

**X-INTERCEPT**is found in 1905 in

*A Brief Course in the Calculus*by William Cain: "The

*x*-intercept of the tangent is found to be 2

*x*

_{1}: prove from this that 'the segment of any tangent to a hyperbola between the asymptotes, is bisected by the point of contact.'" [James A. Landau]