Bryn Mawr College monographs . brightness not a flicker balance. The plan of the apparatusused in making the photometric balance (spectroscope, photo-metric apparatus, etc.,) is indicated in Fig. I. The coloredlight was presented to the eye in the following manner. Theeye-piece was removed from the spectroscope and a lens sys-tem was substituted consisting of two lenses L^ and L„ oneto render the light emerging from the objective slit paralleland the other to focus it on the eye 30 cm. distant. By mean^of an extra set of jaws operating in the vertical, the lengtliof the analyzing slit was redu
Bryn Mawr College monographs . brightness not a flicker balance. The plan of the apparatusused in making the photometric balance (spectroscope, photo-metric apparatus, etc.,) is indicated in Fig. I. The coloredlight was presented to the eye in the following manner. Theeye-piece was removed from the spectroscope and a lens sys-tem was substituted consisting of two lenses L^ and L„ oneto render the light emerging from the objective slit paralleland the other to focus it on the eye 30 cm. distant. By mean^of an extra set of jaws operating in the vertical, the lengtliof the analyzing slit was reduced to a value which gave animage 3 x mm. on the pupil of the observers eye. Ihiadjustment was maintained throughout the work. The size I STUDIES IN PSYCHOLOGYChart V 304 Showing a curve of achromatic sensitivity when the stimuli are made)hotometrically equal at 75 the photometric field was limited by a screen S, containingstmiulus opening 15 mm. in diameter. This screen wasaced 20 cm. from the eye. Between this screen and theUS L. was inserted a small strip of metal, D, the inner edgewhich was carefully beveled. When adjusted to the posV)n used in making the photometric observation, this bisected the photometric field. The surface of this strip^is kept freshly coated with magnesium oxide deposited fromU burning metal. This surface received the light from the^mdard lamp; the other half of the field was filled with lightl)m the spectroscope. The spectroscope and lens systemvre shielded from the standard lamp by suitable screensJ e photometric balance was obtained as follows. The stand-^1 lamp, a seasoned 32 cp. carbon lamp giving the color valuenhe carbon standard of watts per spherical candle, was^ at the position on the bar required to give the desiredi-nsity of light in the photometric field, and the intensity ofcolored light fill
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