PHYSICS OF THE GLOBE. 171 



tu re in the Air, Professors Guldberg and Mohn have also pub- 

 lished a short elementary essay on Vertical Currents in the 

 Atmosphere. They treat of ascending and descending cur- 

 rents, and illustrate their formulae by numerous examples, and 

 especially urge the importance of knowing more than we do 

 about the condition of the outer, or higher, atmosphere with 

 reference to temperature and moisture. 



The relative force of the wind at the ground, and at a con- 

 siderable elevation above, has been studied by J. Stevenson, 

 C.E., of Edinburgh. The observations give in each case a 

 great increase in velocity, but hardly allow of further definite 

 generalization. The experiments on the velocity upon differ- 

 ent sites of a round tower, and between various screens, are 

 very interesting, and show how very local are the indications 

 of an anemometer, and how carefully its site should be selected. 



BAROMETRIC PRESSURE. 



In order to determine the mean barometric pressure at the 

 new Meteorological Observatory at Vienna, Hann has inves- 

 tigated all the barometric observations made in that city 

 since 1775, but finds the uncertainty of the instrumental er- 

 rors and the altitudes such that it is not advantageous to 

 combine them with the recent observations; and therefore 

 relies entirely upon those made since 1852. He closes his 

 paper by deducing the diurnal and annual periodical changes 

 in the pressure. 



Buys-Ballot communicates a highly important memoir con- 

 taining tables of monthly mean pressures at the stations for 

 which the departures are given daily in the Meteorological 

 Bulletin of the Netherlands. The large number of stations, 

 and the careful revision of the data, render this a very wel- 

 come addition to our knowledge of the distribution ofatmos- 

 pheric pressure in Europe. He has also published, in the Aus- 

 trian Meteorological Journal, a table showing the annual bar- 

 ometric variations for 108 stations throughout Europe, as re- 

 sulting from long series of observations, and reduced to a 

 uniform decennium. The discussion of his results he reserves 

 to himself in a future number of his Jaarbooeh. 



Carpmael, of Toronto, gives a formula for the reduction to 

 sea-level of the readings of the barometer. His formulae are 

 convenient, and quite as accurate as the conditions of the 



