Science Sittings

New Zealand Tablet, 23 August 1906, Page 35

Science Sittings

By 'Volt'

Glass that Keeps Out the Heat. An Austrian inventor, Richard Szigmondy, is reported to have ma<le a new kind of window glass whose chief peculiarity is that it prevents the passage of nine-tenths of the heat of the sun's rays. It is well known that ordinary window glass allows nearly all of the heat derived from tub sun to pass through but on the other hand intercepts all heat coming from non-luminous sources, such as a stove or the heated ground. This is the reason why heat accumulates under the glass roof of a hothouse. If coveied with Szigmondy's glass a hothouse would, it is claimed become a cold house, as the heat could not get into it One advantage set forth in favor of the new glass is that a house whose windows were furnished with it would remain delightly cool in summer. But in winter, perhaps, the situation would not be so agreeable. fa How Color Changes in Glass. Changes in the color of glass are caused by subjecting it to the action of what are known as ultraviolet rays of light. Something of the same sort may lie observed on high mountains, where old glass fiom bottles originally green, alter exposure to the light of a great elevation in the legions of perpetual snow attains a beautiful pale purple tint. The same results may also be seen in connection with the glass insulators used on telegraph or telephone lines in mountain districts. During a period of years an observer says that he has found it interesting to watch the changes in hue of ihe insulatoison the telephone line connecting Laggan station of the Canadian Pacific railway with the chalet at Lake Louise. The elevation is l>etween 5000 and (,00u feet, and while the line nins Hirough the fortst almost all the way, the actinic eftect of the light has changed the green of those insulators that have been up for several years to a brilliant purple. Those, that have been in service longest apparently have the deepest tint. Ancient Coined Money. Throughout the eaily parts of Scripture, as well as through the poems of Homer, not a single passage occurs from which can be mfened the existence of stamped money of any description. It is agreed that the Egyptians had no coined money. Herodotus is the authority for the .statement that the Lydians were the first people who coined gold and silver. The Pairan ( liromcle,' however, ascnbcs the first coinage of copper and silver money to Phoidon, King of Argos 805 H.( „ in Aegma, which Aehan corroborates, and' the best numismatic antiquaries agree in considering the coins of Aegina from their aicliaic form and appearance, the most ancient known. They are of, silver and boar on the upper side the figure of a turtle ami on the under an indented mark. Coins are among the most certain evidences of histoiy. In the later part of the Greek series they illustrate the chonoloty of reigns. In the Roman series they fix the date in succession of events. Gibjbon observes that, if all our Historians were last, medals, inscriptions and other monuments would be sulTk-ient to record the travels of Hadrian. The leign of Probus might be written from his coins. The Mystery of Volcanoes The mystery of volcanoes is being gradually cleared up by the investigations of radioactivity, if the conclusions of Major C. I?. Dutton, U.S.A., are correct. It can no longer be supposed that an eruption is an overflow from the earth's molten interior, thirty or lorty miles or more below the surface, but the evidence is strong that the source of the material and is never more than two or three miles deep the quantity is small compared with the mass of the earth— perhaps not more than three cubic miles of lava having been discharged in the greatest recorded outpour. The eruptions, moreover, tend to recur in the same spot— perhaps thousands of times before the activity wanes. This could be explained by assuming that radium is being generated at a depeth of two or three miles in each active crater, as the heat from the breaking up of tlie emanation would, accumulate until sufficient 1o melt a portion of the rocks and on the discharge of the molten mass through the .action of steam or otherwise, the process would be repeated until the exhaustion of the radium.