- Email: [email protected]
The transverse thermo-electric effect in metal crystals
726
CURRENT
TOPICS.
[J. F. I.
The Transverse Thermo-electric Effect in Metal Crystals. P. W. BRIDGMAN. (Proc. Nat. Ad. Sciences, Feb., x927.)-In “ If a bar of crystalline 1851 Lord Kelvin made this prediction: substance possessing an axis of thermo-electric symmetry has its length oblique to this axis, a current of electricity sustained in it longitudinally will cause evolution of heat at one side and absorption of heat at the opposite side, all along the bar, when the whole substance is kept at one temperature.” Voigt in 1910, basing his opinion upon his equations, gave his adhesion to the existence of such an effect. Until Bridgman took up the matter it seems that no one had investigated it. He has discovered the effect in bismuth, zinc, tin and cadmium, using in all cases bars consisting of single crystals and measuring IO cm. in length and 6 mm. in diameter. He used three bismuth bars. In two the basal planes were inclined zoo to the length and in the third it was parallel to the length. The current entered and left by clamps fixed to the two ends of the bar. The temperature difference between the two sides was measured by thermo-elements. When a current of the order of I ampere flowed through the bar the difference of temperature between the two sides was about .4’ C. When the direction of the current was reversed, the side of the bar that had been the hotter became the cooler and vice versa.. The temperature difference seemed proportional to the current strength. It changes in sign if the bar be rotated through 180” without any change in the location of the thermocouples. It does not vary with the position of these along the bar. Thus the whole of one side is cooled while the whole of the other side is warmed. In zinc, calcium and tin the effect was much less. The author maintains that both Voigt and Lord Kelvin made mistakes in the arguments that led them to expect the effect that he has discovered experimentally. G. F. S. Yearly Variation of the Quantity of Ozone in the Upper Atmosphere. F. W. P. GOETZ. (Be&. z. Physik. 21. f. Atmosphere, 13, No. I.)-“ Wave-length 320 pp is the farthest outpost of the solar spectrum, thrust forward1 like an island into the region where ozone absorbs the radiation.” The author makes a study of the intensity of the radiation of this wave-length received from the sun by means of what he designates Filter Cd 320 pp, which seems to be a combination of a cadmium photo-electric cell with a filter permitting only a narrow portion of the spectrum in the designated region to pass, and deduces the quantity of ozone present in the upper air. The relative amounts of this substance in the four seasons are, in arbitrary units, 1922, winter, 97 ; spring, I 12 ; summer, 95.5 ; autumn, 92; and 1923, winter, 103.5 ; spring, 115. He finds that Suering’s observations indicate a similar annual change. At Arosa, where his laboratory is situated, changes in atmospheric pressure and in ozone content take place in opposite directions. G. F. S.
CURRENT
TOPICS.
[J. F. I.
The Transverse Thermo-electric Effect in Metal Crystals. P. W. BRIDGMAN. (Proc. Nat. Ad. Sciences, Feb., x927.)-In “ If a bar of crystalline 1851 Lord Kelvin made this prediction: substance possessing an axis of thermo-electric symmetry has its length oblique to this axis, a current of electricity sustained in it longitudinally will cause evolution of heat at one side and absorption of heat at the opposite side, all along the bar, when the whole substance is kept at one temperature.” Voigt in 1910, basing his opinion upon his equations, gave his adhesion to the existence of such an effect. Until Bridgman took up the matter it seems that no one had investigated it. He has discovered the effect in bismuth, zinc, tin and cadmium, using in all cases bars consisting of single crystals and measuring IO cm. in length and 6 mm. in diameter. He used three bismuth bars. In two the basal planes were inclined zoo to the length and in the third it was parallel to the length. The current entered and left by clamps fixed to the two ends of the bar. The temperature difference between the two sides was measured by thermo-elements. When a current of the order of I ampere flowed through the bar the difference of temperature between the two sides was about .4’ C. When the direction of the current was reversed, the side of the bar that had been the hotter became the cooler and vice versa.. The temperature difference seemed proportional to the current strength. It changes in sign if the bar be rotated through 180” without any change in the location of the thermocouples. It does not vary with the position of these along the bar. Thus the whole of one side is cooled while the whole of the other side is warmed. In zinc, calcium and tin the effect was much less. The author maintains that both Voigt and Lord Kelvin made mistakes in the arguments that led them to expect the effect that he has discovered experimentally. G. F. S. Yearly Variation of the Quantity of Ozone in the Upper Atmosphere. F. W. P. GOETZ. (Be&. z. Physik. 21. f. Atmosphere, 13, No. I.)-“ Wave-length 320 pp is the farthest outpost of the solar spectrum, thrust forward1 like an island into the region where ozone absorbs the radiation.” The author makes a study of the intensity of the radiation of this wave-length received from the sun by means of what he designates Filter Cd 320 pp, which seems to be a combination of a cadmium photo-electric cell with a filter permitting only a narrow portion of the spectrum in the designated region to pass, and deduces the quantity of ozone present in the upper air. The relative amounts of this substance in the four seasons are, in arbitrary units, 1922, winter, 97 ; spring, I 12 ; summer, 95.5 ; autumn, 92; and 1923, winter, 103.5 ; spring, 115. He finds that Suering’s observations indicate a similar annual change. At Arosa, where his laboratory is situated, changes in atmospheric pressure and in ozone content take place in opposite directions. G. F. S.