The diffraction fields near a long, semicylindrical, [Formula: see text] in. diameter rod of lucite, oriented in a nearly plane incident field of 3.2 cm. waves with plane surface towards or away from the source, have been reinvestigated in the region very close to the rod more thoroughly than previously (McLay and Subbarao 1956). The incident field was polarized parallel to the long axis of the semicylinder. In addition, the field near the rod when it was oriented with plane surface aligned with the axis of propagation and the field when the same rod was coated with thin aluminum foil and placed in turn in each of the three above-mentioned orientations have now been observed.A number of features in the diffraction patterns of the uncoated lucite rod have been qualitatively accounted for as resulting from effects of weak radiation after one or more internal reflections, or from evanescent waves close to a part of the surface where internal incidence is at angles greater than critical, superposed on one or more of the incident, directly transmitted and externally reflected radiations. The patterns a little away from the surface of the uncoated rod and the whole patterns of the aluminum-coated one are quite simple relatively and provide evidence of marked near-field diffraction.
