THE OBSERVATIONS OF AIR AND SEA MOTIONS. 



17 



have to mark on it the points which represent the heights of the standard isobaric 

 surfaces. From the records in the case before us these heights are found equal to 

 99, 989, 1970, 3057, 4274 dynamic meters, as noted in column 2 of table C. The 

 corresponding thicknesses of sheet, also expressed in dynamic meters, are given in 

 column 3. These two columns then represent, as we have seen (Statics, sees. 35, 54), 

 the distribution of pressure and mass along the vertical, the thickness of the standard 

 isobaric sheets giving the average specific volume of the air within the sheet. 



4400/ 



600m-bars 



Fig. 34. Construction of average velocities for standard isobaric sheets. 



On the curve we now mark points representing the heights noted in column 2, 

 i.e., the heights of 101, 1009, 2009, 3121, 4362 common meters, and draw the corre- 

 sponding chords. The directions of these chords determined by the transparent 

 sheet (fig. 32) are noted in column 4. Then the lengths of these chords are measured 

 and divided by the thicknesses of sheet, viz, 908, 1000, 11 12, 1241 common meters, 

 respectively. The average velocities found in this way are noted in column 5. 



As the numbers in column 3 represent the average specific volume of the air in 

 the sheets, we get the specific momenta simply by dividing the velocities (column 5) 



