XIX. 



ON THE VIBRATIONS OF AN ATMOSPHERE PERIODICALLY HEATED. 



By Max Margdles. 



The computation of the variations of pressure in the atmosphere 

 arising from periodic changes in temperature has a certain interest in 

 connection with a problem of meteorology that, like all dynamic prob- 

 lems in this field, necessitates very extensive computations. 



The daily variation of the barometer, freed from all non-periodic 

 influences, can be represented very satisfactorily by the super-position of 

 two waves, one of which has a whole day as its period ; the other has 

 the half day. The diurnal wave is undoubtedly an effect of the varia- 

 tion of temf>erature. It appears much stronger on clear days than on 

 cloudy days; it is very slight at sea and shows on the land notable 

 inequalities. The semi diurnal wave is on the other hand of a regular- 

 ity that is uncommon in meteorological phenomena. At places of the 

 same latitude it is of very nearly equal amplitude and of the same 

 phase in reference to the local time. If we consider this wave also as 

 a consequence of the variations of temi)erature, then the connection 

 seems to be obscure. 



The mean daily temperature represented for any place by a curve, 

 can like every such curve, be analyzed into a series of waves of twenty- 

 four, twelve, eight, and six hour periods. Does the twenty-four-hour 

 wave of pressure originate from the corresponding wave of tempera- 

 ture? Does the twelve-hour variation of pressure depend on the 

 twelve-hour temperature variation! Why is the amplitude of the 

 twelve-hour pressure term so large in comparison with the twenty-four- 

 hour term, whereas the reverse is true for the temperature? Whence 

 come the regularity of the one and the local variations of the other? 



These questions have been asked repeatedly. In a memoir recently 

 published,! Hann has given the most' comprehensive and thorough de- 

 scription of the daily oscillation of the barometer, utilizing the rich 



* Trauslateil from the Sitzungsherichte der KonigUch Akademie der Wissenschaften zu 

 Wien (Matli.), 1890, vol. xcix,pp. 204-'2-27. See, also, Exner's E^-jjerforiMm der Plnjsik. 

 1890, Baud xxvi, pp. r)13-G33. 



+ "Unters. ii. d. tiigliche Oscillation d. Barometers," Vienna Denk., vol. 55, 1889, 

 296 



