INSTRUCTIOJSTS FOR MAKING PILOT BALLOON OBSERVATIONS 47 



Tables 1 and 2 were described above under Form No. lllOA-Aer. 

 and Form No. 1110-Aer., respectively. 



Table 3, "Rate of ascent in meters per minute," gives the ascen- 

 sional rates for different weight balloons and for different free Ufts. 

 The argument "free Uft" (1), rangmg from 75 to 195 grams, is found in 

 the vertical column at the extreme left of the table, While the weight of 

 the balloon (w), ranging from 22 to 60 grams at intervals of two grams, 

 is found along the first horizontal line heading each column. 



Table 4 aids in the conversion of Fahrenheit temperatures in degrees 

 and tenths to centigrade degrees and tenths. The range of the table 

 in Fahrenheit temperature is from —36° to 100°, by tenths of degrees. 

 Note that each column of centigrade temperatures is arranged with 

 two columns of Fahrenheit temperatures, one on either side. The 

 values in the centigrade column, when associated with the Fahrenheit 

 column on the left, are as they appear in print, but when associated 

 with the Fahrenheit column on the right the value is reversed. That is 

 5°.0 C. when associated with 41° F. is above zero, but when 

 associated with 23° F. is below zero. The tenths of Fahrenheit 

 degrees are converted by noting the ending of the centigrade tempera- 

 ture for the whole Fahrenheit degree, finding this in the column headed 

 "P. P.," and moving down the scale the .number of spaces equivalent 

 to the number of tenths of degrees to be converted. For instance, a 

 temperature of 58°. 8 F. is equivalent to 14°. 9 C Opposite the whole 

 degree 58 and m the C. column is found 14°. 44. The ending .44 is 

 found in column "P. P." Smce the tenths of a degree to be converted 

 are 8, we move down the column 8 spaces and there find .89; this, 

 when substituted for the ending .44 of the C. value 14.44, gives us the 

 temperature 14.89, or 14°. 9 C. Likewise, any Fahrenheit temperature 

 within the limits stated can be converted to degrees and tenths of the 

 centigrade scale. 



Tables 5 and 6 are self-explanatory. 



VI. TWO-THEODOLITE OBSERVATIONS 



150. Two-theodolite observations. — In two-theodoHte observations 

 the balloon is followed by two instruments, one placed at either end 

 of an accurately measured base fine. Simultaneous readings of the 

 azimuth and elevation angles of both instruments are recorded at the 

 end of each minute. From these angles the position of the balloon at 

 the end of each minute is determined by triangulation. 



151. Two-theodolite observations require the cooperation of three 

 or four men, depending upon the arrangement of stations and scope 

 of work at hand. The prevailing arrangement of double-theodolite 

 stations requires four men for the observational work — an observer 

 and a recorder posted at each station. Their respective duties are 

 nearly identical with those in a single-theodolite observation. When 

 the observmg stations are connected by telephone, then an observa- 

 tion can be carried on with three men. But if computation and plot- 

 ting are carried on during the flight, four will be needed. 



152. Time signaling. — In two-theodolite observations some method 

 of signaling by which the signals are transmitted simultaneously to 

 both stations is absolutely necessary. Regardless of how accurately 

 the angle readings are made, unless they are made at the same instant 

 the results of computations based thereon will be unsatisfactory. The 



