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34
ON RADIATION.
surrounded by a small glass globe to protect it from currents of air; through an orifice in the globe the rays could pass from the spiral and fall afterwards upon a thermo-electric pile. Placing in front of the orifice an opaque solution of iodine, the platinum was gradually raised from a low dark heat to the fullest incandescence, with the following results:—
| Appearance of spiral. | Energy of obscure radiation. | ||
| Dark | 1 | ||
| Dark, but hotter | 3 | ||
| Dark, but still hotter | 5 | ||
| Dark, but still hotter | 10 | ||
| Feeble red | 19 | ||
| Dull red | 25 | ||
| Red | 37 | ||
| Full red | 62 | ||
| Orange | 89 | ||
| Bright orange | 144 | ||
| Yellow | 202 | ||
| White | 276 | ||
| Intense white | 440 | ||
Thus the augmentation of the electric current, which raises the wire from its primitive dark condition to an intense white heat, exalts at the same time the energy of the obscure radiation, until at the end it is fully 440 times what it was at the beginning.
