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SCIENCE. 



[N. S. Vol. XXI. Xo. .5:53. 



ed before being employed in obtaining any 

 definite results. Mr. Clayton's thorough study 

 of the sources of error must also bring up 

 many doubts concerning the accuracy of re- 

 sults obtained by observers who exercise less 

 care. It may be noted that, in Mr. Clayton's 

 opinion, the excessive temperature gradients, 

 greatly exceeding the adiabatic rate, which 

 have several times been referred to in various 

 publications, are probably due, for the most 

 part, to the fact that the observations in ques- 

 tion were not made simultaneously at the two 

 levels (p. 14). Temporary local differences of 

 temperature may also explain gradients which 

 exceed the adiabatic rate (p. 15). 



The interest which attaches to all reliable 

 meteorological data obtained in the free air is 

 so great as to warrant the inclusion, in the 

 pages of Science, of the following summary 

 of the most important points contained in 

 Mr. Clayton's report. 



Diurnal Period of Temperature at Different 

 Heights. — On several occasions observations 

 were obtained during many hours at heights 

 of about 3 Imis., but there was no evidence 

 of any change of temperature due to a diurnal 

 period. On June 18-19, 1900, for example, 

 the temperature at a height of 2,900 ms. was 

 recorded at intervals throughout twenty-four 

 hours, and although there was a general fall 

 under the inflvience of some general atmos- 

 pheric change, there was no appreciable di- 

 urnal period (Fig. 3, p. 16), in spite of the 

 fact that there were only a few cirrus clouds 

 to obscure a small portion of the sky. At 

 1 km. there is a diurnal period of tempera- 

 ture, as is evidenced by numerous records, but 

 with a tendency to a secondary maximum at 

 night as well as by day. A marked feature 

 is also a sudden fall of temperature after sun- 

 rise (about 9 A.M. in summer), the evidence 

 from the movements of the kites at this time 

 being to the effect that the diurnal convec- 

 tional currents from the ground reach the 

 kites then. This 'chilling' of the air at a 

 height of about 1 km. is explained by Mr. 

 Clayton as due to the rise of the ascending 

 currents, on account of their inertia, to an 

 altitude greater than their point of equilib- 

 rium. The ascending air is cooled by adia- 



batic expansion below the temperature of the 

 air into which it penetrates ; hence, at the tops 

 of convectional currents of this kind, rising 

 from the ground, there ought to be a belt of 

 chilled air, above which there must be a higher 

 temperature. Such an inverted temperature 

 gradient is usually found above cumulus 

 clouds. The diurnal change of temperature 

 at the greatest altitude reached by the ascend- 

 ing currents must, therefore, be the opposite 

 of that at the ground, i. e., the temperature is 

 lower by day than by night. The records of 

 May 1, 1902, show clearly that an inversion of 

 tlx march of the diurnal temperature does 

 occur at the top of convectional currents rising 

 from the warm ground (Fig. 4, p. 20), for 

 while at 500 and 1,000 ms. the afternoon maxi- 

 mum is well marked, the temperature curve 

 becomes inverted at 1,230 ms. At 2,000 ms. 

 there is no perceptible diurnal period. This 

 cooling at the tops of convectional currents 

 begins nearer the earth's surface early in the 

 morning, and reaches a maximum altitude 

 about the warmest part of the day. The di- 

 urnal period of temperature at different 

 heights is graphically summarized in Fig. 5 

 (p. 25), and verbally, on p. 29. 



The Diurnal Period of Relative Humidity 

 at Different Heights. — In general, the diurnal 

 period in relative humidity is the inverse of 

 that of the temperature at all levels up to and 

 including 1,500 meters. 



The Diurnal Period in Wind Velocity at 

 Different Heights. — ^Mr. Clayton finds the 

 well-known explanation, given by Espy and 

 Koppen, of the diurnal variation in wind 

 velocity only a partial one, for at night the 

 air from 300 to 1,000 ms. above sea level does 

 not merely resume a velocity of movement 

 proportional to its height, but increases in 

 velocity until its movement is more rapid 

 than that of the air strata above or below the 

 given level. Some other forces must, in Mr. 

 Clayton's opinion, be called into play besides 

 the retardation of the upper currents by as- 

 cending currents from below. It is suggested 

 that, as the atmosphere is trying to maintain 

 a mean velocity of flow having a constant 

 value for the vertical section above any given 

 point on the earth, if in any given part of 



