Chart 4 represents the Luminosity of gas from a batswing burner reduced to one, two and three candle power at one foot distance.

1
Candle		 2
Candles		 3
Candles		 Total.
Theoretical21+21+21=63
Physiological 21+3+7=31

Chart 5 represents the Luminosity of a hand Paraffin Lamp similarly reduced.

1
Candle		 2
Candles		 3
Candles		 Total.
Theoretical21+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:—

Six slips of the sensitized papers were covered by a thin metal plate, pierced by six rows of apertures, a complete row lying over each sample of paper. The rows contained seven apertures each, one being left uncovered to receive the full energy of the impinging light. The remaining six were covered respectively by a Red, Orange, Yellow, Green, Blue or Violet standardized screen of 15 units colour intensity; the whole was fitted into a suitable exposure frame. Many exposures were made, from which the four following were selected:—

No. 1. 20 min. exposure to a dull sky.
No. 2. 10 min. exposure to bright sunlight.
No. 3. 20 min. exposure to bright sunlight.
No. 4. 30 min. exposure to bright sunlight.