Page:Popular Science Monthly Volume 28.djvu/180

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tion. (A good idea of such a precipitation is had by observing the particles of water condensed from transparent vapor, in unusually high thunder-heads, where the action is in some respects similar.) Between those ascending columns are seen descending masses of cooler vapors, rendered dark and smoky by relatively cool and opaque particles of carbon, all or most of the other elements being still maintained by the excessively high temperature in the condition of transparent vapor. In the immediate region, however, where the cyclone is raging, these bright ascending columns are drawn out horizontally by the inrushing metallic winds (which often reach a velocity of a thousand miles per hour) into long filaments, pointing in general toward the center of the disturbance, which is always occupied by a huge black cloud of smoke (frequently twenty thousand miles in diameter) rapidly settling back into the interior of the sun. Over and across this great central black cloud are often driven long arms of the shining carbon-clouds, which, when the cyclonic action is very strong, bend round into slowly changing spiral forms, very suggestive of intense action. A striking illusion, invariably connected with this sight, is that the observer seems to be viewing it from a position quite near the scene of the disturbance, whose minute and complicated details are seen with exquisite distinctness.

After witnessing such a spectacle, the observer must have felt great admiration for the men who have devised and successfully constructed an instrument capable of showing in action such enormously energetic forces, the very existence of which would otherwise hardly have been conceived.

But, although the refracting telescope has now been brought to such exquisite perfection, the first ones were exceedingly crude, and it is interesting to trace the gradual development of the telescope from a simple pair of spectacle-glasses, suitably placed one behind the other, into the great refractors of Washington, Vienna, and Pulkowa, which are monuments of optical and mechanical ingenuity.

Spectacles were invented about the year 1300, but it was not until 1608 that a Dutch spectacle-maker, as a pretty experiment, combined two such lenses in a way that made distant objects look nearer. A rumor of this invention reached Galileo, at Venice, in 1609, and interested him so much that, before he had even seen one of them, he reasoned the problem out for himself, and in a few days produced a telescope which made distant objects appear to bo only one third as far away as they actually were, by cementing a suitable spectacle-glass in each end of a lead organ-pipe. With this instrument the astonished senators of Venice derived great amusement in spying out ships at sea from the top of the great bell-tower.

So industriously did Galileo follow up his first achievement, that soon he had constructed more than one hundred telescopes of various sizes, one of which made objects look eight times nearer; and, finally,