the Civil Law, a disposition of a testament, whereby the testator substitutes one heir for another, who has only the usufruct, and not the property of the thing, left him.

Subtraction, or Subtraction, in Arithmetic, the second rule, or rather operation, in arithmetic, whereby we deduct a less number from a greater, to learn their precise difference. See Arithmetic and Algebra.

Subtangent of a curve, the line that determines the intersection of a tangent with the axis; or that determines the point wherein the tangent cuts the axis prolonged.

Subtense, formed from sub "under," and tendo "I stretch," in Geometry, a right line which is opposite to an angle, and drawn between the two extremities of the arc which measures that angle.

Subterraneous, whatever is under ground: thus naturalists speak of subterraneous fires, subterraneous damps, &c.

Subterraneous Cavern. See Quarries.