ABSTRACTS: METEOROLOGY 317 



vations of meteors, (3) Observations of twilight phenomena, (4) Obser- 

 vations of auroras, (5) Observations of noctilucent clouds, 



Chief facts of observation: (1) At and beyond 11 kilometers up to the 

 greatest elevation yet reached, about 30 kilometers, the temperature 

 is substantially constant at any given time and place, (2) The humidity 

 of the upper atmosphere is vanishingly small, (3) The upper atmosphere 

 consists in part of hydrogen and helium, (4) The atmosphere is 

 sufficiently dense at an elevation of, 150 kilometers to fire meteors, 

 (5) The atmosphere at 70 kilometers elevation still scatters a percepti- 

 ble amount of light. 



Chief inferences: (1) The temperature of the upper atmosphere is 

 substantially constant with respect to elevation far beyond the limits 

 yet reached by sounding balloons, (2) The upper atmosphere is prac- 

 tically free from vertical convection, (3) The volume percentages of the 

 gases at the beginning of the isothermal region are the same as those 

 of dry air at the surface of the earth, (4) Above this level the lighter 

 gases gain in percentage with increase of elevation, (5) Above 75 kilo- 

 meters, mass-density and light-intensity soon decrease very slowly 

 with increase of elevation, while below this level they soon increase 

 rapidly with decrease of elevation, (6) Above 75 to 80 kilometers dust 

 falls comparatively rapidly, while below this level it settles more and 

 more slowly, (7) There is no level at which either mass-density or light- 

 intensity changes in any sense abruptly with changes of elevation. 



W. J. H. 



METEOROLOGY.— Echelon clouds. W. J. Humphreys. Bulletin of 

 the Mount Weather Observatory, 4: 409-411. 1912. 



Under certain conditions a great many small cumulus clouds appear 

 with flat bases, and all at substantially the same elevation. When 

 viewed from a point to one side and at a lower level such a cloud forma- 

 tion appears in perspective like a series of inverted terraces, or like an 

 extensive inverted flight of steps. 



The meteorological meanings of the cloud phenomena just described 

 are, among others : (a) That the cloud bases are all on about the same 

 level, (6) That the vertical distribution of water vapor is essentially 

 the same over all the region covered by the clouds in question, (c) That 

 the change of temperature with altitude above any given place in this 

 region is substantially the same as it is above any other, (d) That the 

 amount of humidity is rather large, (e) That vertical convection is 

 occurring in many separate places, but nowhere violently. W. J. H. 



