Charts 3, 4 and 5 deal with experiments, with one, two and three standard candles of the London Gas Referees. The curves represent the physiological rate of declining luminosities by distance. Some characteristic differences from other lights are brought together in Charts 4 and 5. The slight irregularities in the curves are probably due to the readings being made at half unit intervals. These acting sometimes in opposite directions, fully account for want of symmetry in the curves. A noticeable feature in these experiments is the small amount of physiological luminosity added by each successive candle to the first. Theoretically, if one candle equals 21 units intensity, two should equal 42, and three 63, whereas the physiological additions of luminosity are not only much less, but vary with different luminous intensities, as will be seen by the following comparisons:-- 1 2 3 Candle Candles Candles Total. Theoretical 21 + 21 + 21 = 63 Physiological 21 + 3 + 6 = 30 Chart 4 represents the Luminosity of gas from a batswing burner reduced to one, two and three candle power at one foot distance. 1 2 3 Candle Candles Candles Total. Theoretical 21 + 21 + 21 = 63 Physiological 21 + 3 + 7 = 31 Chart 5 represents the Luminosity of a hand Paraffin Lamp similarly reduced. 1 2 3 Candle Candles Candles Total. Theoretical 21 + 21 + 21 = 63 Physiological 21 + 3 + 6 = 30 PHOTOGRAPHIC ENERGIES OF DIFFERENT RAYS The following experiments are preliminary only, and were undertaken to determine the relationship of the several colours of the tintometrical scales, to their associated photographic values, under different conditions of light and times of exposure, the end in view being the hope of standardizing screens, papers and impressions. The standardized colours act as selective light absorbents on the same principle as screens for trichromatic colour work, but differ from these in their having a definite standard of colour depth and colour purity. Work of this character requires paper of a known degree of sensitiveness, but on inquiry it was found that no reliable standard had as yet been established. On this, six makes of “white” paper were purchased in the open market and submitted to exposures under the following conditions:--