. Physical researches on sensation [by] Frank Allen [and others]. by making upt»n different portions of whatwas thought to be the ((juivalent «»f a spectrum of uniform luminosity,we may infer that while the wave length varied with each observation,the intensity oi the light as observed in the eye—piece of the spectro-meter remained constant for all ;<ervations. Take for example, thedata furnisheil by the third observation in the table referred to is shown tluMe that tiie anunmt of light going through the nicolsat the beginning of \\w observation is represented b
. Physical researches on sensation [by] Frank Allen [and others]. by making upt»n different portions of whatwas thought to be the ((juivalent «»f a spectrum of uniform luminosity,we may infer that while the wave length varied with each observation,the intensity oi the light as observed in the eye—piece of the spectro-meter remained constant for all ;<ervations. Take for example, thedata furnisheil by the third observation in the table referred to is shown tluMe that tiie anunmt of light going through the nicolsat the beginning of \\w observation is represented by -IITH. whilethe aniount oi light going through at the end of the observation isrepiesented by -1840 showing that -OliTO of the total intensity of thespectrum where the wave length equaled 491/^. had ti * ■ Ided to 236 THE ROYAL SOCIETY OF CANADA •1170 of total intensity to produce a change in the sensation that wasjust perceptible. This portion of light reduced to the intensity of thestandard of brightness at the polariser was found to be represented. Intensit-y by 58 as shown in the table, which gives us the least perceptible in-crement with an intensity at the polariser equal to the intensity ofthe standard. Now, as already stated, the intensity of the light under [nkelin] THi: Si:NSrn\E.\ Ol the eye to LKJHT 237 obseivutiuii is represented by IITO of the total inteiij«ity of the i»pec-truin in portion observetl. Hut fraction of total inteiusity jjivena luminosity in the eye-piece e<iujil to tlie stundarii of brightnenswliich ia tiiis paper is represented by unity, and all portions of thespectrum, as observed, were of tH4ual brif:htnesH. Therefore, we mayrepresent the huninosity of each of those portions by unity, and hencealso their intensities as observed in the eye-piece by unity. NowKfinigs Law stated matliematically is of the fornj Ui (1 -t-Di) =k whereDi represents tiie least perceptible increntent and I a constant in-tensity in tiie source of
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