140 



MILLIKAN— METEOROLOGICAL WORK 



other words, since the sixth root of 2 is 1.13, at a height of 6,000 

 meters, the velocity should be about 13 per cent, greater than at the 

 surface. Such an increase in velocity would be very easily observ- 

 able in the experimental data. The fact that it is not found there 



Pilot balloon ascent showing isolated convection current. 



is due to the wholly fortuitous circumstance that the slow diffusion 

 of hydrogen through the walls, as observation by Blair and Sherry 

 has shown, is just sufficient, with the balloons here used, to retard 

 the ascensional rate enough to make it quite exactly constant. 



This makes it possible, provided one could always duplicate the 

 size and weight of his balloon, to obtain a very exact determination 

 of wind velocity and direction by a one-theodolite method, the 

 height being always known from the time and the known rate of 

 ascent. 



