Bulletin of the Bureau of Standards Volume 5, Nos. 93-115

Bulletin of the Bureau of Standards Volume 5, Nos. 93-115

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1909 edition. Excerpt: ... first approximation to the intensity sensibility of the average human eye over a wide range of color and intensity. 13. THE LUMINOUS SENSATION, FECHNER'S LAW. Accepting, then, for the photometric function or least perceptible increment the form P=Pm+(l-Pm) (/ //)- as a tentative working basis, we may apply the theory of sensibility to find the scale reading--which is luminous sensation in this case. P is expressed as a fraction (P--SI/I) in the above function, so that sensibility, being inversely proportional to &/, is inversely proportional to IP. Calling sensibility Sz and the constant of proportionality Kn then hi Ip i(pm+(i-pm)(i0jiy) But from the theory of sensibility the sensation of visual brightness B is the general integral of the sensibility with respect to the stimulus, hence J J/(Pm+(i-Pm)(/D//)") =f og(i+pm(i"io"-i)yln plus an integration constant which is zero, since the sensation B approaches zero as the stimulus / approaches the threshold value I0. About eighty years ago E. H. Weber observed that the least perceptible increment to a stimulus affecting several of the sense organs, under fixed subjective conditions of attention, expectation, and fatigue, bore a definite relation to the amount of that stimulus. G. T. Fechner, thirty years later, extended Weber's observations and formulated his results in mathematical terms. Calling the stimulus / and the least perceptible increment 61, then Fechner's statement of what he termed Weber's Law is that B1:1=constant. This law appears to hold over a wide range of ordinary working intensities, breaking down only for very low and for excessively intense stimulation. Fechner proceeded further by assuming that the above constant was proportional to the...show more

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  • Paperback | 122 pages
  • 189 x 246 x 7mm | 231g
  • Rarebooksclub.com
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 1236529898
  • 9781236529893