22 INSTRUCTIONS FOR MAKING PILOT BALLOON OBSERVATIONS 



This formula has not as yet been completely verified, except for a 

 limited range of free lifts. A free lift of 450 grams with hydrogen gas 

 or 503 grams with helium is now being used, however, which have 

 been determined quite definitely to give an ascensional rate of 280 

 meters per minute. For observations made with these balloons (with 

 such free lifts) the additive corrections to the ascensional rate for the 

 first 5 minutes are: 25, 14, 10, 7, and 4 percent, respectively. 



55. For higher free lifts the tentative ascensional rates of the 100- 

 gram balloons, when inflated with helium gas, are as follows: 



56. Inflation of balloons. — The balloon may either be filled to a con- 

 venient size and the ascensional rate determined from the weight of 

 the balloon and the free lift, or the ascensional rate may be decided 

 beforehand and the proper free lift given to the balloon. The former 

 method is known as "indefinite" inflation, and the latter method as 

 "definite" inflation. The ascensional rate in either case may be readily 

 determined from table 2. Definite inflation can be accomplished only 

 with the aid of some filling apparatus, which should be sufficiently 

 sensitive to register the weight of the balloon and the free lift to the 

 nearest whole gram. 



57. Balloons should always be inflated in a well-ventilated place, 

 but one well sheltered from drafts and currents. The presence of these 

 disturbances, though small, materially affects the determination of 

 the proper ascensional rate. 



58. Inflation balance. — The Weather Bureau has adopted a stand- 

 ard ascensional rate of 180 meters per minute for the 30-gram bal- 

 loons. The proper inflation is accomplished by means of a special 

 inflation balance shown in figure 10. This is an ordinary gram bal- 

 ance, which is adapted for this use by placing a hydrogen line on the 

 balance which terminates in a nozzle on one of the balance pans for 

 attaching the balloon. The ordinary weighing bar is replaced by a 

 special bar upon which are engraved two scales, one above the other. 

 The lower scale is an ordinary gram scale for weighing the balloon, the 

 upper scale is graduated in accordance with the ascensional rate for- 

 mula, in this case to give an ascensional rate of 180 meters per minute. 

 For other ascensional rates, different graduations must be made for 

 this scale. 



59. The graduations of the ascensional rate scale are based on the 

 principle of moments, thus (M—l) a=rx, where M=the mass of the 

 counterweight; l=free lift of the balloon; a=10 cm. lever arm of 

 balance; r=20 gram rider; and a;=distance in centimeters graduation 

 is from the fulcrum. 



60. In order to allow greater range for the lower scale (gram scale), 

 the right-hand pan of the balance is weighted in such a manner 

 as to throw the zero point on the bar under the left-hand knife edge. 



61. A three-way stopcock is placed in the gas line in order that gas 

 may be released in case the balloon is accidentally overfilled. 



62. This balance may be used also for the inflation of larger balloons, 

 such as the 100-gram pilot balloon, in which case it is equipped with an 



