Let L = {l1 ..., l(n)} be a collection of n lines in three-dimensional
space. A joint of L is a point incident to three noncoplanar lines of
L. We prove that the number of joints of L is O(n23/14 log31/14 n), w
hich is O(n1.643). This improves a previous bound of O(n7/4) due to Ch
azelle et al. The proof makes use of recent range searching techniques
and of a structural analysis of the pattern of intersections between
n lines in space. (C) 1994 Academic Press, Inc.