54 THE NEW WORLD OF SCIENCE 



_ m 



in which V represents the rate of ascent in meters per minute, 

 / is the free lift, or the weight of the displaced air less the 

 weight of the balloon and contained hydrogen, L is the weight 

 of the balloon plus the free lift and K is a constant. 



The formula as modified by the observers of the Signal Corps 

 is 



.208 



This formula is found to fit the observational data within the 

 ranges used in the Signal Corps work to an accuracy of some- 

 what less than 10 per cent., which is sufficient for most work 

 at the front. 



2. Meteorology in the Aid of the Artillery. In former times 

 when guns did not shoot to a greater distance than eight or ten 

 miles, it was usually possible to observe where the projectile 

 hit and to correct by (f spotting." This made unnecessary the 

 correction of the trajectory for the influence of the wind and 

 the changing density of the air with increasing altitude. In the 

 present war, however, guns have been built to shoot much 

 farther and in addition camouflage has prevented the visual 

 location of guns even at the old ranges. Hostile batteries have 

 been located in many instances solely by the new art of sound- 

 ranging which has itself demanded for the high accuracy at- 

 tained aerological data. The answering battery has been 

 obliged to fire wholly by the map, so that it is obvious that it 

 has become necessary to make careful allowances both for the 

 density of the air and the direction and speed of the wind at 

 various altitudes. Some of the modern projectiles remain in 

 the air as long as seventy seconds and a moderate wind blow- 

 ing across the path of such a projectile might easily cause it to 

 drop half a mile away from the point at which it would strike 

 if fired in still air. The wind-direction and speed at various 

 altitudes have been obtained, as already indicated by pilot bal- 



