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Page:Popular Science Monthly Volume 24.djvu/711

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But, unlike the risk from collision with another ship, the risk from collision with icebergs can not be diminished by any system of side-lights or head-lights or stern-lights, except in just such degree (unfortunately slight) as a powerful light at the foremast-head, aided by strong side-lights or bow-lights, may serve to render the gleam of the treacherous ice discernible somewhat farther ahead. But to a steam-ship running at the rate of fourteen or fifteen knots an hour, even in the clearest weather, at night, the distance athwart which a low-lying iceberg can be seen, even by the best eyes, is but short. She runs over it before there is time for the watch to make their warning heard, and for the engineers to stop and reverse their engines.

But science, besides extending our senses, provides us with senses other than those we possess naturally. The photographic eyes of science see in the thousandth part of a second what our eyes, because in so short a time they can receive no distinct impression at all, are unable to see. They may, on the other hand, rest on some faintly luminous object for hours, seeing more and more each moment, where ours would see no more—perhaps even less—after the first minute than they had seen in the first second. The spectroscopic eyes of science can analyze for us the substance of self-luminous vapors or of vapors absorbing light, or of liquids, etc., where the natural eyes have no such power of analysis. The sense of feeling, or rather the sense for heat, which Reid originally and properly distinguished as a sixth sense (not to be confounded, as our modern classification of the senses incorrectly confounds it, with the sense of touch), is one which is very limited in its natural range. But science can give us eyes for heat as keen and as widely ranging as the eyes which she gives us for light. It was no idle dream of Edison's, but a thought which one day will be fraught with useful results, that science may hereafter recognize a star by its heat, which the most powerful telescope yet made fails to show by its light. Since that was said, the younger Draper (whose loss followed so quickly and so sadly for science on that of his lamented father) has produced photographic plates showing stars which can not be seen through the telescope by which those photographs were taken. As yet the delicate heat-measurers devised by science have not been applied to astronomical research with any important results. But Edison's and Langley's heat-measurers have been used even in this way, and the very failure which attended the employment of Edison's heat-measurer (the tasimeter, or, literally, the strain-measurer, described shortly before in the "Times") during the eclipse of 1878 shows how delicate is the heat-estimating sense of science. When the light of the corona—which has no heat that the thermometer, or even that far more delicate heat-measurer, the thermopile, will recognize—fell on the face of the tasimeter, the index which Edison supposed likely, to move just perceptibly actually flew beyond the index-plate. Thus, though the heat of the corona could not be measured, the extreme