PLANE STRAIN IN BIPOLAR CO-ORDINATES. 
293 
straight edges and minimum stress at the points of the straight edge immediately 
opposite the centre of the hole. Moreover as the radius of the hole is increased in 
proportion to the distance of its centre from the edges of the strip these maxima and 
minima become more pronounced. In all the cases examined experimentally the 
minimum stress in the straight edge remains a tension, but Prof. Coker surmises that 
if the radius of the hole were still further increased in proportion to the width of the 
strip this minimum stress would become a compression. All these results agree 
qualitatively with the theoretical results established in this paper for the semi-infinite 
plate, and allowing for the difference in the two problems they may be taken as a 
substantial experimental verification. 
