182 



SCIENCE 



[N. S. Vol. XLIX. No. 1260 



to be dynamic rather than static. It is hard 

 to conceive of a quiescent electron. 



William Albert JSToyes 



SOME RECENT CONTRIBUTIONS TO 

 THE PHYSICS OF THE AIR. II 



BAROMETRIC FLUCTUATIONS 



Another meteorological phenomenon that 

 has been the subject of numerous investiga- 

 tions, is the pressure of the atmosphere. This 

 pressure imdergoes many changes, and the 

 causes of some of them, such as its variations 

 between summer and winter, and between 

 ocean and continent, have long been Imown. 

 But the causes of certain others, notably the 

 great changes that accompany cyclones and 

 anticyclones, have not yet been fully deter- 

 mined. Neither of these classes of changes, 

 that is, those whose causes have long been 

 known, and those whose causes still remain 

 partially obscure, will be discussed here, though 

 each is important and full of interest. But 



there are two other classes, namely, baro- 

 metric ripples, and the pressure wave of semi- 

 diurnal period, that, because of their obvious 

 interest to physicists, will be briefly con- 

 sidered. 



Barometric "Ripples." — Small pressure 

 changes having amplitudes usually of 0.1 mm. 

 to 0.3 mm. and periods of 5 minutes to 10 

 minutes, and continuing for hours or even 

 days together, are very common during cold 

 weather. They are not greatly different in 

 magnitude from the well known wind effects 

 on the barometer, but obviously of different 

 origin since their amplitude has no relation 

 to the local wind velocity. 



Their explanation appears to lie in the fact 

 that whenever layers of air that differ in 

 density at their interface flow over each other, 

 long billows, analogous to water waves, and 

 generated in the same way, are produced. If, 

 now, the under layer is colder than the upper, 

 as it is during the radiation or surface in- 

 versions of winter, and rather shallow, 100 



EE 





tSO- 



^0^ 



-30- 



FiG. 4. Barometric Eipples. 



