from the transformation expands very little with rising temperature, if indeed it does not contract. Its'course seems to be a prolongation of s-iron below the A s point. When iron is cooled down it goes through the changes of length in the reverse order.
G.F.S.
Discussion on the Electrical State of the Upper Atmosphere. (Proc. Royal Soc., A757.)--The importance of this subject in present scientific thought is attested by the discussion held by the Royal Society on March 4th and by the lecture delivered at The Franklin Institute five days later by Dr. E. O. Hulburt on " The Kennelly-Heaviside Layer and Radio-wave Propagation."
In opening the discussion Sir Ernest Rutherford pointed out that the existence of a conducting layer in the atmosphere is required to explain the daily variation of the earth's magnetism according to the views of Schuster and Chapman and also to account for the passing of, electric waves around the earth. Eccles and others have shown that a region of ionized gases can both absorb and refract electrical waves passing through it. In this connection Sir Joseph Larmor has demonstrated by theory that the considerable length of the free path of the electrons in the higher atmosphere is of palmary importance in causing reflection and scattering of the waves. Rutherford himself feels that it is not yet known whether the electric waves that come down from the Heaviside layer are there reflected as from a mirror or are refracted so as to return to the earth.
S. Chapman states that through simultaneous readings of temperature and pressure made on sounding balloons we know the value of these two quantities in the air to a height of 25 km. From the average temperature at the surface of the earth of 285 ยฐ abs. the temperature falls to 22o ยฐ at the height of IO km. Thence it remains constant up 25 or 3 ยฐ km. From their observations on meteors Lindemann and Dobson inferred that the temperature of 22o ยฐ persists to an elevation of 5 ยฐ or 6o km. and that above this height there is a rather rapid rise of temperature to about 3oo ยฐ abs. at 14o km., where the air is warmer than at the ground. He finds it difficult to account for the presence of nitrogen and oxygen at the height of 5oo km. By McLennan and Shrum's identification of auroral lines with lines of these gases they should exist wherever the aurora appears.
C. T. R. Wilson emphasized the importance of thunder storms upon the electrical state of the upper air. Statistical studies show that I8OO storms are going on all the time and that ioo flashes of lightning occur in a second. " Thus the power expended in producing lightning by all the thunder clouds in action at a given time is of the order of lO TM watts or IO TM ergs per sec., i.e., about I/IO,OOO of the energy received by the earth from the sun per sec." It may be that the thunder clouds maintain the potential difference of I,OOO,OOO volts that exists between the upper atmosphere and the earth and in some manner balance the downward current of IOOO amperes that flows