Abstract: Schemes intending to improve Weber's law have been often proposed during the past hundred years. Yet none of them can be regarded as a successful rule to reveal the general relationship between stimulation inte- nsity and difference threshold of a certain receptor. The DL theorem derived from the model of stimulation and effect fo- rmerly given by the author is shown to be in sound agreement with sensa- tion experiments from simple hand weighing to that of illumination with Weber's ratio varying more than a hundredfold. Besides, examination of the verified data gives evidence that the accomodation of visual sensibility under daily life illumination of 10~(-3) --10~3 millilambert is mainly accomplished by the change of the pupil; that in the range of intermediate vision, the chief analyzer of the eye is the cone itself; and that the illumination intensity about the upper limit of the mentioned range can also be estimated by the DL theorem.

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