228 REPORTS OF INVE;STIGATI0NS AND PROJECTS. 



national Committee for Aeronautic Meteorology. Sufficient observations for 

 working out examples of the practical use of these methods in case of the 

 sea are not at hand. The main difficulty to overcome has been that the ob- 

 servations give only the horizontal components of the motion, while methods 

 for directly observing the vertical motions have not yet been found, either 

 for the case of air or sea motions. In spite of their smallness, these motions 

 are, however, of extreme importance meteorologically, as governing mainly 

 the distribution of precipitation and of clear sky. Fortunately they can be 

 derived indirectly if the horizontal motions are sufficiently well known. 

 This derivation depends upon a proper use of the surface condition and on 

 the equation of continuity. For the use of the surface condition proper 

 topographic charts must be at hand. The world's map drawn for this pur- 

 pose (see previous reports), and the special charts required for the working 

 out of special examples are now nearly ready. The constructions based upon 

 the use of the equation of continuity, referred to in the previous reports, 

 have been still further developed and tried practically upon material of ob- 

 servations, both from the ground and from higher levels in the atmosphere. 



Complete charts of the velocity of the medium being produced, the next 

 kinematic problem is that of producing corresponding charts of the accelera- 

 tions. These will form the basis of the later dynamic investigations. The 

 methods of constructing these charts have been developed and tried practi- 

 cally in the extent in which proper material of observations has been avail- 

 able for us. The acceleration on the motion relatively to the earth and the 

 acceleration due to the coexistence of this relative motion and the motion of 

 rotation of the earth must be derived separately. The latter partial accelera- 

 tion can be found at once, as soon as the charts representing the velocities 

 have been produced. 



The method of constructing charts of the horizontal and vertical compo- 

 nents of this acceleration have been worked out and tried practically for the 

 case of motions near the earth's surface. The application of the construction 

 and the representation of the vector for higher levels has not yet been tried 

 practically, but is expected to contain no special difficulty. 



Satisfactory material of observation for trying practically the methods of 

 drawing charts of the acceleration relatively to the earth has not yet been 

 available for us. As the knowledge of these accelerations will be of funda- 

 mental nature for the further dynamic investigations. Professor Bjerknes 

 brought before the International Committee for Aeronautic Meteorology, 

 at its meeting at Monaco this year, a series of proposals regarding the organi- 

 zation of aerologic observations. As a resolution in favor of these proposals 

 was voted, it is to be hoped that observations making possible a more thor- 

 ough discussion of the aerial dynamics will be produced in the coming years. 

 Meanwhile it will probably be possible to get unpublished material of obser- 



