-------+------+----------------+----------+------------------ | | Red. | Yellow. | Blue. | +----------------+----------+------------------ Inches |Light | “Carmine.” | “Lemon.” | “Cobalt.” Square.|Units.| | | | +-----+-----+----+----+-----+-----+-----+------ | | R. | Or. |Blk.| Y. | Or. | B. | Vi. | Blk. -------+------+-----+-----+----+----+-----+-----+-----+------ 2 | 10 |20·2 | ·3 | ·5 | 6·9| ·1 |11·5 | ----| ---- 4 | 14 |19·1 | ·4 | ·5 | 6·9| ·1 |11·5 | ----| ---- 6 | 14 |18·95| ·59| ·46| 6·9| ·1 |10·7 | ·2 | ·1 8 | 16 |16·9 | 1·1 |----| 7·0| ----|10·5 | ·5 | ---- 10 | 20 |16·9 | 1·1 |----| 7·0| ----|10·5 | ·5 | ---- 12 | 22 |16·9 | 1·1 |----| 7·0| ----|10·5 | ·5 | ---- Open | | | | | | | | | 24 | 26 |16·9 | 1·1 |----| 7·0| ----|10·5 | ·5 | ---- -------+------+----------------+----------+------------------ -------+------+----------------+----------------+------------ | | Orange. | Green. | Violet. | +----------------+----------------+------------ Inches |Light | “Chrome.” | “Emerald.” |“Fr. Mauve.” Square.|Units.| | | | +----+----+------+----+----+------+-----+------ | |Or. | R. |Light.| Gr.| Y. |Light.| Vi. | R. -------+------+----+----+------+----+----+------+-----+------ 2 | 10 | 6· | 3·4| ·05 | 6·4| ·2 | ·05 | 7·4 | 3· 4 | 14 | 6· | 3·4| ·05 | 6·4| ·2 | ·05 | 7·4 | 3· 6 | 14 | 6·2| 3· | ·05 | 6·4|----| ·05 | 7·2 | 3· 8 | 16 | 6· | 3· | ---- | 6·6|----| ·2 | 7·2 | 2·8 10 | 20 | 6· | 3·2| ---- | 6·6|----| ·2 | 7·2 | 2·8 12 | 22 | 6· | 3·2| ---- | 6·6|----| ·2 | 7·2 | 2·8 Open | | | | | | | | | 24 | 26 | 6· | 3·2| ---- | 6·6|----| ·05 | 7·2 | 2·8 -------+------+----------------+----------------+------------ CHAPTER XII. The Physiological Light Unit. DIFFUSED LIGHT. The physiological values of light intensities determined by the absorptive method, differ in some respects, from the intensities based on the inverse ratio of the squares of distance between the shadows of two lights. However valuable this method of calculating light intensities may be from a mathematical point of view, it does not express the physiological appreciation of light differences. The dimensions of the light unit used in the following experiments have already been described. This method cannot deal exhaustively with intense direct lights, on account of the presence (activity) of the disturbing red ray which prevents total absorption. Such lights must first be modified by intercepting media of known diffusive value, or by reflection from a white surface.