DISTRIBUTION OF ATMOSPHERIC PRESSURE VON BEZOLD 373 



of any such surface, but that as a basis for theoretical considerations, 

 especially of acceleration, it must always be used circumspectly. 



It is quite otherwise with the presentation of atmospheric pres- 

 sure by a vertical section, which, as before stated, has been desig- 

 nated by the inappropriate name "presentation by surfaces of 

 pressure." This method is difficult to put into practice since the 

 pressure surfaces can be determined only by a roundabout process, 

 but it offers many advantages from a theoretical point of view. 



It is because of this peculiarity that the " vertical sections of iso- 

 bars," as they should be called, are relatively seldom used and even 

 then almost never applied to specific cases, but only schematically 

 for purely theoretical considerations. 



So far as I know, the first one to make use of this method was 

 Julius Hann, who according to his own statement explained it in 

 1875 in his university lectures and also deduced the law of the acceler- 

 ation experienced by a particle of air at any point on an isobaric 

 surface. 



The first more detailed publication in reference to this point is 

 found in Hann's memoir on "Mountain and Valley Winds." 8 Sub- 

 sequently H. Januschke 7 in 1882 and L. Teisserenc de Bort 8 in 

 1884 made use of this method of presentation. It would lead us 

 away too far to develop the general formula for such an isobaric sur- 

 face, although this could easily be done with the help of the well- 

 known barometric formula, but of course with the uncertainty 

 inherent in this formula relative to the vertical distribution of tem- 

 perature and moisture. 



On the other hand, certain properties of this surface may at least 

 be mentioned here. 



If there are given two surfaces of constant pressure, one of which 



corresponds to the atmospheric pressure/?, the other to /? -f- J/?, then 



the vertical distance between these surfaces at any point is given by 



the equation 



A/3 

 Ah = 13.6 — (3) 



since p A h is the mass of the air contained in a vertical cylinder 

 or prism standing on the unit of surface and 13.6 A /3 is the corre- 

 sponding mass of mercury. 



6 J. Hann: Zeit. d. Oest. Gesel. f. Met. 1879, XIV, p. 444. Compare 

 also my note 11, Memoir XVII, p. 354 of this collection of translations. 



7 H. januschke: Zeit. d. Oest. Gesel. f. Met. 1882, XVII, p. 136. 



8 L. T. de Bort: Annales du Bureau Central. Ann£e 1882, pp. 73-80. 

 Paris, 1884. 



