A Weissenberg hheogoniometer was m ~d i f i e d l -~ to improve sample temperature uniformity and constancy (to within f0.5'C) and to give a quicker response to normal thrust changes (estimated gap change 50.1 fim/kg thrust; gap angle = 8.046'; gap radius = 1.2 cm; servomechanism replaced by an open-loop cantilever spring of 10 kg/pm stiffness). Low-density polyethylenes (IUPAC samples A and C, melt index at 190'C = 1.6) at 150'C were used in step-function shear rate experiments. Inspection of marked sectors in the samples showed substantial uniformity of shear at values of = 10 sec-' and S I 2 shear units (S = At), the shear was highly nonuniform at and near the free boundary. Using selected premolded samples A, scatter in seven replicate tests at = 1.0 sec-' did not exceed f 6 % for N l ( t ) and f 5 % for u ( t ) (N1 = primary normal stress difference; u = shear stress; t = time of deformation from the initiation of experiment at zero time). N I ( ~) and a ( t ) data agreed with Meissner's'; for S = 0.1, 2.0, 5.0, and 10.0 sec-I, torque maxima occurred at S = 6 shear units, and thrust maxima occurred in the range of 10 to 20 shear units. a ( t ) and N l ( t ) data do not satisfy the van Es and Christensen4 test for rubber-like liquids with strain rate invariants included in the memory function. On cessation of shear (after a shear strain S at constant shear rate s), initial values of -d u ( t ) / d t and -d N l ( t ) / d t were found to depend strongly on S, in some cases passing through maxima as S was increased. After shearing at = 0.1 sec-' for 500 sec, such that stresses became constant, stress relaxation data satisfied Yamamoto's5 equation of d N l ( t ) / d t = -2Su(t). = 0.1, 2, and 5 sec-'; for