Four experiments addressed the relevance of the eigenvalues I k of the inertia tensor for perceiving length by dynamic touch. Experiments 1-2 focused on the consequences of limiting variation in the minimum eigenvalue 1 3 , Both revealed that perceived length is a function of I k . Whether the contribution of 1 3 is detected, however, depends on the range of values that characterize a particular object set. Experiments 3-4 considered the relationship between an independent index of a rod's diameter, which does not affect I k , and actual manipulation of a rod's diameter, which does affect I k • Whereas the former appeared as satisfaction of implicit instructions to alter reports of perceived length, the latter entailed actual differences in perceived length in accordance with I k • Results are discussed with respect to the links among actual length, perceived length, and I k , as well as, in particular, how these links guarantee that perceived length is in the range of actual lengths.When an object is grasped firmly in the hand and vielded out of view by means of movements at the wrist, ts length can be perceived. A large number ofexperiments lave shown that perceived length is a function not of the ibject's actual length but rather of its resistance to rotaional acceleration as quantified by the inertia tensor, 1/ see Appendix). In the initial research directed at the spaĩ al abilities of dynamic touch, measurements were reitricted to the coordinate-system-dependent components if Ii}, and then only to its moments of inertia, lxx,~vY' and