248 PROGRESS OF METEOROLOGY IX 1889. 



(1861), that the morning maximum of pressure is due to a reaction of 

 the upper cloud layers against the expanding lower air, and finds that 

 the results of observations at Calcutta, Melbourne, and Batavia are, 

 on tbe whole, favorable to this hypothesis, since the morning maximum 

 of pressure approximately coincides with the instant when the temper 

 ature is rising most rapidly. At tropical stations the barometric max- 

 imum follows the time of most rapid heating by a shorter or longer 

 interval, but this may probably be attributed to the action of con- 

 vection which must accelerate the time of most rapid heating near the 

 ground surface; while the barometric effect, if real, must be deteniiineii 

 by the condition of the atmosphere up to a great height. With refer- 

 ence to Lamont's criticism of Espy's theory, a condition is pointed out 

 which alters the data of the problem, viz, the resistance that must be 

 offered to the passage of the jjressure wave through the extremely cold 

 and highly attenuated strata of the upper atmosphere. With respect 

 to the evening maximum of pressure it is pointed out that in India, 

 and also at Melbourne, there is a strongly marked minimum of cloudi- 

 ness between sunset and midnight, which on the average coincides with 

 the evening maximum of the barometer. In the author's opinion these 

 and other facts seem to indicate a compression and dynamic heating of 

 the cloud-forming strata, and that therefore the diurnal barometric 

 oscillations are dynamic phenomena. {Nature, xxxviii, p. 70.) 



Mr. H. H. Clayton has a jiaper on the annual and diurnal periods of 

 the barometer. Iteferring to the result pointed out by General Greely 

 that the epochs of maxima and minima of air jiressure show a coinci 

 dence. the author traces the probable cause of the occurrences of the 

 maxima to the expansion and overflow of air from Asia and America 

 to the pole; and of the minima at the pole to the fact that the overflow 

 from the pole towards those continents is not replaced by an influx in 

 that direction from the oceans. The retardations of the annual maximum 

 from the Arctic region to the equator, and of the minimum from the 

 southern parts of the continent to the Arctic region, is also attributed 

 to the relative heating and cooling of the continent and oceans. {Am. 

 Meteor. Journal, Ti, p. 150.) 



Mr. A. Angot, in a paper on the diurnal variation of the barometer 

 {Atmuaire Soc. Meteor, de France), finds that thediurnal variation results 

 from the superposition of two distinct waves. One of these is expres- 

 sible as a harmonic function, the constants of which depend on the 

 latitude and geographical features ; this wave is due to the diurnal 

 variation of temperature of the air near the earth's surface. 



The second wave has a semi diurnal period and its amplitude varies 

 with the latitude of the place and with the declination of the sun. 



Dr. J. Hann has made an exhaustive investigation of the diurnal 

 range of the barometer over the globe. He has calculated the harmonic 

 co-efficients for each month, and for the year, for a large number of 



