seems very -difficult to believe that the light of a fire-fly, for instance, is accompanied by a temperature of 20000 F. or more, which is what we should have to produce to gain it by our usual processes. That it is, however, not necessarily impossible, we may infer from -the fact that we can, by a known physical process, produce a still more brilliant light without sensible heat, where we are yet sure that the temperature exceeds this. No sensible heat accompanies the fire-fly's light, any

more »

... than need accomnpany that of the Geissler tube; hut this might be the case in either instance, even though heat were there, owing to its minute quantity, which seems to defy direct investigation. It is usually assumed, with apparent reason, that the insect's light is produced without the invisible heat that accompanies our ordinary processes; and this view is strengthened by study of the fire-fly's spectrum, which has been frequently observed to diminish more rapidly toward the red than that of ordinary flames. Nevertheless, this, though a highly probable and reasonable assumption, remains assumption rather than proof, until we can measure with a sufficiently delicate apparatus the heat whichl accompanies the light, and learn not only its quantity, but, what is more important, its quality. Apart from the scientific interest of such a demonstration, is its economnic value, whiclh may be inferred from what has already been said. It therefore seems desirable to make the light of the fire-fly the subject of a new