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Uses of colored glass
March, I917. ]
CURRENT TOPICS.
37r
about 3 feet thick and one 9 to IO feet thick. They are separated by beds of limestone of other varieties and make up only about 2o per cent. of the stone that must be removed. The remaining 8o per cent., however, is available for crushed and pulverized limestone, chicken grit, and other uses, and considerable quantkies were marketed for these purposes in I916. The greatest difficulty in the development of lithographic-stone quarries in the United States has been the high cost of quarrying and preparing the stone in competition with the well-known Bavarian stone. Much of this stone is reported to occur in thin layers that require only planing and polishing before use, whereas all known deposits in the United States that are at all suitable for lithographic work occur in more massive beds that must first be sawed into slabs of proper thickness. High cost of labor in the United States and of railroad as compared with ocean transportation have also stood in the way of the domestic industry. Quarrying of the Bavarian stone, however, involves the handling of large quantities of waste, and the waste piles around the quarries to-day form hills of considerable size. The marketing of crushed stone and similar products from the Brandenburg quarry should go far toward eliminating the cost of quarrying from the expense of preparing lithographic stone. With this advantage it may be possible, even after the European war is over, to market the Kentucky stone in competition with the Bavarian stone, the better grades of which under normal conditions bring 5 to 6 cents a pound for IO by i2 inch slabs, and the poorer grades T~/~ cents a pound for slabs of the same size. Uses of Colored Glass. H. P. G.'~GI~. (Transactions of the Illu,ginatin9 Engineering Society, vol. xi, No. 9, P- Io59, December 30, 1916.)---The uses of color in illuminating engineering may be divided into direct decorative effects, colored illumination for aesthetic effects, and illumination for. specific visual effects. The direct decorative uses are seen m the stained glass windows of churches and in the coloring of illuminating reflectors and shades. Such decoration borders on the colored enamel such as is used in china and porcelain. Colored illumination is used in stage lighting and to produce the much desired warm tones in interior illumination. In these cases the light from the original source is filtered through either a colored lamp bulb or through a colored enclosing globe or even reflected from a colored reflector. The illumination for specific visual effects includes protection either of the eye or the work from harmful radiations. An example of the latter is the use of a red light for photographic purposes where the plate is not sensitive to red and the eye is. Protection of the eye from harmful radiation may consist in the removal of the ultra-violet such as is met with in experimenting
372
CURRENT ToPIcs.
[J. F. I.
with the arc lamp or in arc welding. It is, moreover, possible, although the eye was developed for use in natural daylight, that in such daylight the radiation in the ultra-violet is harmful and that under favorable conditions it will cause cataract in the course of several years. Excess of visible or luminous radiation produces discomfort to the eye, and if the eye is continuously exposed to too great illumination, injury results. Intra-red radiation when not accompanied by excess of ultra-violet or luminous radiation is not generally regarded as harmful. It must, however, be recognized that such radiation is uncomfortable to the workers in low temperature light sources such as glass and steel furnaces. Anything that causes continued discomfort to the eye in the course of years must result in permanent damage. In this connection, it is interesting to note that the use of ordinary clear spectacles reduces the discomfort from such light sources. As aids to vision, monochromatic light sources have been found to give the greatest possible visual actuity. Such monochromatic light may be the mercury arc and a suitable glass; or the spectrum of white light shortened by filtering through colored glass. The use o f " noglare " and orange glass reduces the length of the spectrum to about one-half and one-fourth respectively. It appears, however, that the increase in visual acuity is accompanied by a corresponding increase in eye fatigue and, for visual comfort, the complete spectrum is most desirable. This seems reasonable because the eyes of the human race were developed in an illumination of natural daylight. For correct color rendering, that is, the same as obtained by natural daylight, the light must have been the same distribution of energy as natural daylight and must appear the same color. Such artificial ligh.ts are the Moore-light, the arc light, filtered through a checker board made of colored glasses, or the light from a tungsten lamp filtered through suitable dyed gelatines or colored glasses. Practical glass filters have been made which transmit approximately 15 per cent of the light from the gas-filled tungsten lamp operating at 285 o° absolute. This low transmission is an objection from the standpoint of the user, but is not prohibitive considering the high original efficiency of gas-filled lamps. The Thermo-Electric Properties of Fused Metals. C.R. DARLING and A. W. GRACE. (Proceedings of the Physical Society of London, vol. xxix, Part I, p. 82, December 15, I916.)--In measuring high temperatures by the thermo-electric method, it has hitherto been customary to regard the melting point of either member of the couple of the extreme temperature capable of being measured. As pyrometers of this type are now constructed, the fusion of either metal causes a break in the circuit, and hence for temperatures exceeding Iooo ° C., it has been found necessary to use junctions of
CURRENT TOPICS.
37r
about 3 feet thick and one 9 to IO feet thick. They are separated by beds of limestone of other varieties and make up only about 2o per cent. of the stone that must be removed. The remaining 8o per cent., however, is available for crushed and pulverized limestone, chicken grit, and other uses, and considerable quantkies were marketed for these purposes in I916. The greatest difficulty in the development of lithographic-stone quarries in the United States has been the high cost of quarrying and preparing the stone in competition with the well-known Bavarian stone. Much of this stone is reported to occur in thin layers that require only planing and polishing before use, whereas all known deposits in the United States that are at all suitable for lithographic work occur in more massive beds that must first be sawed into slabs of proper thickness. High cost of labor in the United States and of railroad as compared with ocean transportation have also stood in the way of the domestic industry. Quarrying of the Bavarian stone, however, involves the handling of large quantities of waste, and the waste piles around the quarries to-day form hills of considerable size. The marketing of crushed stone and similar products from the Brandenburg quarry should go far toward eliminating the cost of quarrying from the expense of preparing lithographic stone. With this advantage it may be possible, even after the European war is over, to market the Kentucky stone in competition with the Bavarian stone, the better grades of which under normal conditions bring 5 to 6 cents a pound for IO by i2 inch slabs, and the poorer grades T~/~ cents a pound for slabs of the same size. Uses of Colored Glass. H. P. G.'~GI~. (Transactions of the Illu,ginatin9 Engineering Society, vol. xi, No. 9, P- Io59, December 30, 1916.)---The uses of color in illuminating engineering may be divided into direct decorative effects, colored illumination for aesthetic effects, and illumination for. specific visual effects. The direct decorative uses are seen m the stained glass windows of churches and in the coloring of illuminating reflectors and shades. Such decoration borders on the colored enamel such as is used in china and porcelain. Colored illumination is used in stage lighting and to produce the much desired warm tones in interior illumination. In these cases the light from the original source is filtered through either a colored lamp bulb or through a colored enclosing globe or even reflected from a colored reflector. The illumination for specific visual effects includes protection either of the eye or the work from harmful radiations. An example of the latter is the use of a red light for photographic purposes where the plate is not sensitive to red and the eye is. Protection of the eye from harmful radiation may consist in the removal of the ultra-violet such as is met with in experimenting
372
CURRENT ToPIcs.
[J. F. I.
with the arc lamp or in arc welding. It is, moreover, possible, although the eye was developed for use in natural daylight, that in such daylight the radiation in the ultra-violet is harmful and that under favorable conditions it will cause cataract in the course of several years. Excess of visible or luminous radiation produces discomfort to the eye, and if the eye is continuously exposed to too great illumination, injury results. Intra-red radiation when not accompanied by excess of ultra-violet or luminous radiation is not generally regarded as harmful. It must, however, be recognized that such radiation is uncomfortable to the workers in low temperature light sources such as glass and steel furnaces. Anything that causes continued discomfort to the eye in the course of years must result in permanent damage. In this connection, it is interesting to note that the use of ordinary clear spectacles reduces the discomfort from such light sources. As aids to vision, monochromatic light sources have been found to give the greatest possible visual actuity. Such monochromatic light may be the mercury arc and a suitable glass; or the spectrum of white light shortened by filtering through colored glass. The use o f " noglare " and orange glass reduces the length of the spectrum to about one-half and one-fourth respectively. It appears, however, that the increase in visual acuity is accompanied by a corresponding increase in eye fatigue and, for visual comfort, the complete spectrum is most desirable. This seems reasonable because the eyes of the human race were developed in an illumination of natural daylight. For correct color rendering, that is, the same as obtained by natural daylight, the light must have been the same distribution of energy as natural daylight and must appear the same color. Such artificial ligh.ts are the Moore-light, the arc light, filtered through a checker board made of colored glasses, or the light from a tungsten lamp filtered through suitable dyed gelatines or colored glasses. Practical glass filters have been made which transmit approximately 15 per cent of the light from the gas-filled tungsten lamp operating at 285 o° absolute. This low transmission is an objection from the standpoint of the user, but is not prohibitive considering the high original efficiency of gas-filled lamps. The Thermo-Electric Properties of Fused Metals. C.R. DARLING and A. W. GRACE. (Proceedings of the Physical Society of London, vol. xxix, Part I, p. 82, December 15, I916.)--In measuring high temperatures by the thermo-electric method, it has hitherto been customary to regard the melting point of either member of the couple of the extreme temperature capable of being measured. As pyrometers of this type are now constructed, the fusion of either metal causes a break in the circuit, and hence for temperatures exceeding Iooo ° C., it has been found necessary to use junctions of