INSTRUCTIONS FOR MAKING PILOT BALLOON OBSERVATIONS 33 



ment, is certain to result in the satisfactory collection of aerological 

 data. 



98. Night observations. — In order to provide upper-air wind data 

 every 6 hours, as is now required along the airways, approximately 

 half of all pilot-balloon observations must be made during the hours 

 of darkness. Such observations are made possible by attaching a 

 suitable light to the balloon. A small paper lantern and candle are 

 usually used for this purpose. The combined weight of the lantern 

 and candle is 18 to 20 grams. Normally the candles will burn ap- 

 proximately 40 minutes. Lanterns and candles are packed in sepa- 

 rate packages for shipment to stations, the former being folded or 

 crushed nearly fiat for that purpose. Before using, therefore, it is 

 necessary to attach the candle to the inside bottom of the lantern 

 while the lantern is still in the folded position. A simple method of 

 doing this is to open the flap in the top of the lantern, light the candle 

 and tip it so that a few drops of melted wax will fall on the bottom of 

 the lantern; then extinguish the candle and quickly press it down on 

 the melted wax and hold it there until the cooling wax holds it fast. 

 One end of a piece of small cord, or thread, 3 to 5 feet long, should 

 then be tied to the wire handle or bail of the lantern. The other end 

 of the cord is to be tied to the balloon after the latter has been in- 

 flated. The use of two pieces of cord with two or three lengths of 

 small rubber bands inserted between them has been found to be ad- 

 vantageous in releasing balloons with lanterns attached. The rub- 

 ber bands reduce the usual jerk given to the lantern upon release and 

 the swinging of the lantern after release. An electric-lighting device, 

 consisting of a small two-cell battery and flashlight lamp, is also used 

 by the "Weather Bureau at certain Pacific coast stations during the 

 season of forest-fire hazard, and at other stations during the winter 

 months when high surface winds make it difficult to light and release 

 the usual paper lantern. The electric devices are, however, heavier, 

 more expensive, and less efficient than the paper lanterns. 



99. Inflation of balloons when lanterns or electric lights are used. — 

 In obtaining the weight of the combination, the additional weight 

 of the lantern, or electric device, should be considered as part of the 

 weight of the balloon ; that is, if the weight of the balloon is 30 grams 

 and the lantern 10 grams, the balloon should be filled the same as if 

 it weighed 40 grams. It is necessary, of course, to have the equiva- 

 lent weight of the lantern or electric device on the pan of the balance 

 beneath the balloon when it is inflated. "When lanterns are used, 

 that fact should be indicated on Forms No. lllOA-Aer. 



100. Lighting lanterns. — Care should be taken not to light the candle 

 too near the hydrogen supply or the inflated balloon. Whenever pos- 

 sible this should be done in the open air, or, if this is not practicable, 

 in a well-ventilated room. (See paragraph No. 68.) Experience has 

 shown that the candle may be successfully lighted in the open air, 

 even when high surface winds are blowing, if placed in a cylindrical 

 receptacle such as a waste-paper basket or bucket. 



101. Theodolite-lighting device. — In order to make night observa- 

 tions, as is now the practice at all stations, it is necessary to provide 

 for the illumination of the cross hairs and verniers. To that end, all 

 of the older theodolites have been so equipped, and all those pur- 

 chased in recent years have been supplied with suitable lighting de- 

 vices by the manufacturer. Current for the operation of the lighting 



