DISTRIBUTION OF ATMOSPHERIC PRESSURE VON BEZOLD 375 



Or if we recall that the angle a is always very small so that we 

 can consider sine and tangent as equivalent, we have: 



"The acceleration experienced by a particle of air at a given point 

 on an isobaric surface is equal to that which a heavy mass would 

 experience if- it could slide without friction on a similar rigid iso- 

 baric surface." 



This theorem holds good in general without reference to the 

 density of the air, that is to say, without reference to the absolute 

 value of the pressure or the temperature. These two quantities 

 or the equivalent density of the air have already exerted their 

 influence on the form of the isobaric surfaces and therefore do not 

 need to be further considered in the final result. 



"Therefore the presentation by the isobaric surfaces allows of 

 direct conclusions as to the gradient-acceleration, and the density 

 of the air at different points of the space under consideration, and, as 

 to the course of the temperatures between neighboring isobaric 

 surfaces." 



Since these conclusions are all rigorous, therefore the unprejudiced 

 consideration of any such presentation suffices to answer the indi- 

 vidual questions, whereas in the use of the ordinary charts of isobars 

 one must always proceed with caution and must consider attendant 

 circumstances. 



Unfortunately this great advantage of the presentation by vertical 

 surfaces suffers from one defect, that the construction of the isobaric 

 surfaces or their intersections with a vertical surface, offers the 

 greatest difficulties practically, so that, as above remarked, it is 

 generally only employed for schematic considerations. 



