WHILE not presuming to offer an explanation of the isothermal or relatively warm stratum in the high atmosphere, which the recent letters in NATURE have made known to others than meteorologists, I desire to point out that it is probably a universal phenomenon, existing at some height all around the globe. This inversion of temperature was first discovered by M. Teisserenc de Bort with the ballons-sondes sent up from his observatory at Trappes, near Paris, in 1901, and almost simultaneously by Prof. Assmann from similar German observations. Since then almost all the balloons which have risen more than 40,000 feet above Central Europe (that is, near latitude 50°) have penetrated this stratum, without, however, determining its upper limit. Teisserenc de Bort early showed that its height above the earth, to the extent of 8000 feet, varied directly with the barometric pressure at the ground. Mr. Dines (NATURE, p. 390) gives the average height of the isothermal layer above England as 35,000 feet, with extremes of nearly 50 per cent. of the mean. Observations conducted last March by our indefatigable French colleague, Teisserenc de Bort, in Sweden, just within the Arctic circle, showed that the minimum temperature occurred at nearly the same height as at Trappes, namely, 36,000 feet, although Prof. Hergesell, who made use of ballons-sondes over the Arctic Ocean, near latitude 7.5° N., during the summer of 1906, concluded that the isothermal stratum there sank as low as 23,000 feet.