X 5370 in the green, one at X 5130 in the greenish blue, and one at X 5030 in the blue. A beautiful collection of diamond crystals belonging to Professor Maskelyne phosphoresces with nearly all the colours of the rainbow, the different faces glowing with different shades of colour. Diamonds which phosphoresce red generally show the yellow sodium line on a continuous spectrum. In one Brazilian diamond phosphorescing a reddish-yellow colour I detected in its spectrum the citron line characteristic of yttrium. The rays which make the diamond phosphoresce are high in the ultra-violet. To illustrate this phosphorescence under the influence of the ultra-violet rays, arrange a powerful source of these rays, and in front expose a design made up of certain minerals, willemite, franklinite, calcite, etc. phosphorescing of different colours. Their brilliant glow ceases entirely when a thin piece of glass is interposed between them and the ultra-violet lamp.
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