Other noticeable points are the small action under the Orange, Green and Violet screens, and the greater, although variable proportion of colour to black under all the colour screens. TRICHROMATIC COLOUR SCREENS. Table VIII contains the colour measurements of five sets of screens for trichromatic colour work which have come from time to time under the writer’s notice. The measurements are the tintometrical colour units required to match the screens under daylight conditions, and are classified under the theoretically accepted terms of Red, Green and Violet. TABLE VIII. ----+-------------------------+-------------------------+-------------------- Set.| RED SCREENS. | GREEN SCREENS. | VIOLET SCREENS. ----+-------------------------+-------------------------+-------------------- No.| Red. Or. Vi. Light. | Yel. Green. Or. Light. | Blue. Green. Black. 1 |119·0 ---- ---- 1·6 | 27·0 36·0 ---- 9·0 | 32·0 1·4 6·6 2 | 24·2 +·8 ---- ---- | 8·9 ---- ·1 ---- | 13·0 ---- 3·1 3 | 26·4 ---- ·8 ---- | 7·5 ---- 1·4 ---- | 16·6 ---- 3·2 4 | 22·6 ---- ---- ---- | 7·6 ---- 1·4 ---- | 15·3 ---- 3·1 5 | 21·0 ---- 9·0 ---- | 28·0 14·0 ---- ---- | 28·0 ---- 2·8 ----+-------------------------+---------------------------+-------------------- The Red screens are all practically pure except No. 5, which transmits also 30 per cent. Violet. No. 1 is distinguished by its greater colour depth and purity, the degree of which latter is recorded at 1·6 light units brighter than standard. In the Green division, only Nos. 1 and 5 transmit any green, No. 1 transmitting also 42·8 per cent. yellow and being 9·0 units brighter than standards; No. 4 transmits 66·6 per cent. yellow to 33·3 per cent. green; Nos. 2, 3 and 4 are all yellows tinged with orange. In the Violet division, Nos. 2, 3, 4 and 5 are all pure blues; No. 1 is tinged with green. Appendix I COLOUR EDUCATION The time has passed when it might have been considered necessary to preface a handbook on the teaching of colour by arguments to prove that it is a legitimate subject of instruction in schools, but it has not hitherto been sufficiently recognized that the early stages of such instruction must be on sound lines and that nothing must be taught which will afterwards have to be unlearned.