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To the Editor:—I have read Professor Bielschowsky's paper on "Divergence Excess" and the discussion which followed it in the August issue of the Archives of Ophthalmology (12: 157, 1934) with much interest and profit. There is one statement, however, which it seems to me should not be allowed to pass without comment. It is as follows : "One can obtain a result as reliable as that obtained by the occlusion test in the following way: By carefully examining the duction power one determines the strongest prism which the patient is able to overcome. At the moment when diplopia appears the rotation prism is replaced by a dark red glass. A patient with exophoria will see crossed double images, the distance of which from each other corresponds initially to the angle of the strongest prism the patient had been able to overcome but very soon diminishes by a few