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The transverse magneto-resistance effect in single crystals of iron
238
CURRENT TOPICS.
[J. F. I.
Measurements of the A m o u n t of O z o n e in the Earth's Atmosphere and Its Relation to Other Geophysical Conditions. G. M. ~B. DOBSON, D. N. HARRISON and J. LAWRENCE. (lProc. Roy. Soc., A 7 6 8 . ) - - A spectrographic method is available for determining the total amount of ozone in the earth's atmosphere above any point. By grants from the Royal Society five such instruments were made and located in England, Ireland, Scotland, Germany and Switzerland. The Smithsonian Institution also provided for a sixth spectrograph which was sent to Chile. Two series are given, containing the monthly averages of ozone content above O x f o r d from February to October, inclusive, for the years 1925 and 1926. In both years the means for September and October are the smallest, though the order is reversed in the second vear. Again in both years the average for February to June is distinctly larger than for the four succeeding months, the relation being in the ratio of 6: 5. Further in both years the March mean is greater than that of February, while that of April is larger than the March mean. F r o m May onwards there is in general a fall in the value of the mean until September ends. With the single exception of June all the means for 1925 are larger than for 1926. In 1925 the February mean is I42 per cent. of the October mean. In the next year the relation is I2o per cent. A comparison of the ozone content with sun-spot activity and with diurnal range of the horizontal component of the earth's magnetic field is favorable to the existence of a connection though definite proof is still lacking. " Almost without exception the ozone value is high in marked cyclonic systems and low in anti-cyclonic systems." A marked correlation is shown between ozone content and atmospheric pressures at heights from 9 to 14 km. G.F.S. The Transverse Magneto-resistance Effect in Single Crystals of Iron. W . L . WEBSTER. (Proc. Roy. Soc., A 7 6 8 . ) - - R o d s were made from single crystals of iron with their axes parallel to the (IOO), the ( I I O ) or the ( I l l ) crystal axis. The rods were about I8 ram. long with a square cross-section 1 mm. on a side. A constant current of 1. 5 amperes flowed along the length of the rods and the resistance was measured by a differential method. The rods were placed in the air-gap of a large electromagnet capable of giving a field of 27,ooo gauss. The lines of force were at right angles to the length of the rods which were rotated about their axes to get different orientations. The presence of a field below 50oo or above 12,ooo gauss always causes a decrease in the electrical resistance of the iron that is about in proportion to the field strength. " In the region between, there occurs a rapid change of resistance which is positive when the current is along a cubic axis and negative for the other two directions; and whose magnitude depends on the direction of the magnetic field, vanishing when the field is along a cubic axis." G. F. S.
CURRENT TOPICS.
[J. F. I.
Measurements of the A m o u n t of O z o n e in the Earth's Atmosphere and Its Relation to Other Geophysical Conditions. G. M. ~B. DOBSON, D. N. HARRISON and J. LAWRENCE. (lProc. Roy. Soc., A 7 6 8 . ) - - A spectrographic method is available for determining the total amount of ozone in the earth's atmosphere above any point. By grants from the Royal Society five such instruments were made and located in England, Ireland, Scotland, Germany and Switzerland. The Smithsonian Institution also provided for a sixth spectrograph which was sent to Chile. Two series are given, containing the monthly averages of ozone content above O x f o r d from February to October, inclusive, for the years 1925 and 1926. In both years the means for September and October are the smallest, though the order is reversed in the second vear. Again in both years the average for February to June is distinctly larger than for the four succeeding months, the relation being in the ratio of 6: 5. Further in both years the March mean is greater than that of February, while that of April is larger than the March mean. F r o m May onwards there is in general a fall in the value of the mean until September ends. With the single exception of June all the means for 1925 are larger than for 1926. In 1925 the February mean is I42 per cent. of the October mean. In the next year the relation is I2o per cent. A comparison of the ozone content with sun-spot activity and with diurnal range of the horizontal component of the earth's magnetic field is favorable to the existence of a connection though definite proof is still lacking. " Almost without exception the ozone value is high in marked cyclonic systems and low in anti-cyclonic systems." A marked correlation is shown between ozone content and atmospheric pressures at heights from 9 to 14 km. G.F.S. The Transverse Magneto-resistance Effect in Single Crystals of Iron. W . L . WEBSTER. (Proc. Roy. Soc., A 7 6 8 . ) - - R o d s were made from single crystals of iron with their axes parallel to the (IOO), the ( I I O ) or the ( I l l ) crystal axis. The rods were about I8 ram. long with a square cross-section 1 mm. on a side. A constant current of 1. 5 amperes flowed along the length of the rods and the resistance was measured by a differential method. The rods were placed in the air-gap of a large electromagnet capable of giving a field of 27,ooo gauss. The lines of force were at right angles to the length of the rods which were rotated about their axes to get different orientations. The presence of a field below 50oo or above 12,ooo gauss always causes a decrease in the electrical resistance of the iron that is about in proportion to the field strength. " In the region between, there occurs a rapid change of resistance which is positive when the current is along a cubic axis and negative for the other two directions; and whose magnitude depends on the direction of the magnetic field, vanishing when the field is along a cubic axis." G. F. S.