32 INSTRUCTIONS FOR MAKING PILOT BALLOON OBSERVATIONS 



94. Recording msibi/ity. — At any convenient time during the ascen- 

 sion the visibility will be noted and recorded according to the follow- 

 ing scales: 



Visibility scale Limiting 



distances 

 Scale Descriptive term (meters) 



Dense fog. — prominent objects not visible at 50 



1 Very bad. — prominent objects not visible at 200 



2 Bad — prominent objects not visible at 500 



3 Very poor — prominent objects not visible at 1, 000 



4 Poor — prominent objects not visible at 2, 000 



5 Indifferent — prominent objects not visible at 4, 000 



6 Fair — prominent objects not visible at 10, 000 



7 Good — prominent objects not visible at 20, 000 



8 Very good — prominent objects not visible at 50, 000 



9 Excellent — prominent objects visible beyond 50, 000 



This scale is nearly self-explanatory. The distances can be laid 

 off on a map of the section of the country, and prominent objects 

 selected as the points of reference. 



95. At night the visibility will be determined from the farthest 

 light that may be seen by the observer, and its distance recorded 

 according to the visibility scale. 



96. Omission of observation. — It sometimes happens that, at the 

 time of the scheduled pilot-balloon observation the weather condi- 

 tions are such that an observer might carelessly or indifferently call 

 off an ascension when it is really possible to make a satisfactory 

 observation. For example, a light sprinkle of rain might be used as 

 an excuse by the observer to call off the ascension, even when the 

 drops are so few as to cause neither injury to the theodolite, discom- 

 fort to the observer, the early disappearance of the balloon, nor 

 appreciable retardation in the ascensional rate of the balloon. Snow 

 flurries of short duration often preclude an ascension at the scheduled 

 time, when shortly thereafter an ascension would be easily possible 

 and worth while. It is expected, therefore, that an ascension will 

 be made within 1 hour before or 4 hours after the scheduled time, as 

 indicated in paragraph No. 69, if weather conditions are such as not 

 positively to forbid the making of an ascension. It is recognized 

 that there are times when it would be a waste of balloon and gas to 

 attempt an ascension; but, on the other hand, conditions must not 

 be too easily and quickly dismissed as belonging to this class. In 

 general, it may be said that an ascension should be made under all 

 conditions except those which incur danger to the instrument, marked 

 discomfort and possible injury to the health of the observer, or a 

 loss of the balloon below 1,000 feet above the surface if within the 

 scheduled 2-hour period or below 2,000 feet if it is a delayed observa- 

 tion. See paragraph No. 69. 



97. It is recognized that, in the last analysis, the question of omit- 

 ting an ascension is one that must be decided locallv, and that no 

 ironclad rules can be set down in instructions. But it is a question 

 that has a strong personal element, and is one that must be answered 

 conscientiously by those concerned. Times when ascensions are 

 likely to be omitted owing to unfavorable weather conditions are 

 often those which would be of greatest scientific value. The observer 

 should bear in mind at all times the value of the data he is securing 

 and the manv uses to which thev may be put, and he should try to 

 cultivate such a spirit of sincerity. This, coupled with good judg- 



