135 the gamma-gamma prime interfaces. Figure 5.16 shows these interfacial dislocations. The beam direction is along the B = . The dislocation images are consequently from the overlapping regions of gamma and gamma prime, regions B, C, D, and E in Figure 5.4. The fact that this network forms as a result of the mismatch between the gamma-gamma prime phases means that the dislocation spacing will be representative of this mismatch (Lasalmonie and Strudel, 1976). The measurement of the mismatch using this method was not attempted here. The dislocations are imagable at the gamma-gamma prime interface, for example, with B = [001]. The network is comprised primarily of dislocations of the following Burger's vectors: b = + [110] and + 1/2[110]. The nodes at the intersections of these two orthogonal dislocation types may be relaxed, resulting in fourfold nodes of dislocations corresponding to Burger's vectors of + 1/2[10T], + 1/2[Oil], + 1/2[Oil], and + 1/2[101]. Any low index two beam imaging condition near B = [001] will always yield some visible set of these dislocations. As an example, Figures 5.16a, a g = (220), B = [001[ image, and 5.16b, a g = (220), B = [001] image, show opposite sets of primary dislocations, as expected from the g*BxU=0 criterion for edge dislocation invisibility (Edington, 1976). These figures do not show the fourfold nodes plainly.