PILOT-BALLOON ASCENSIONS AT SEA 



103 



each side of the quarter-deck. It was possible to sight 

 forward a distance of seventy-five feet from these sta- 

 tions, and no other positions could give greater distance. 

 The seams in the deck assisted greatly, first in laying 

 out the base lines, and, subsequently, in orienting the 

 theodolite during observations. 



When the base lines were laid out, the quarter-deck 

 theodolite stations were chosen so that the instrument 

 would be centered over a particular seam; the seam 

 then was followed forward and, as it happened, the verti- 

 cal edge of a supply bin was found to coincide with the 

 seam. Supply bins being identically located on both 

 sides of the forward deck, two parallel base lines were 

 readily obtained which were in turn parallel with the 

 ship's keel. 



When the instrument was set up for a period of ob- 

 servation, one tripod foot was pointed forward and set 

 on a seam; the other feet were set on a line at right 

 angles to the seams and spread over a certain number 

 of seams to make the tripod head level. The tripod feet 

 were prevented from spreading beyond a certain amount 

 by being wired together, near the ends, with wires radi- 

 ating from a central ring, all the wires lying close to 

 the deck when the instrument was in use. After the ini- 

 tial choosing of the proper seams, it was but a brief 

 task to repeat a set up when desired. Speed in setting- 



up and in other preliminary preparations, was essential 

 when rapid variations in cloud formations allowed only 

 short intervals for observations. 



Personnel. --The preliminary preparations on the 

 Carnegie required the presence of two men for about ten 

 minutes; the observations (by sextant and theodolite) re- 

 quired the presence of three men for a few minutes to 

 more than an hour, according to conditions of cloud and 

 weather; the subsequent computations and reductions re- 

 quired the time of one man (for an average series of 

 twenty minutes) for about two hours, or more if the ser- 

 ies of observations were longer. 



If morning and afternoon observations were to be 

 carried out by future expeditions, in conformity with 

 land stations in the United States, the entire time of one 

 man would have to be devoted to the work and the assist- 

 ance of two, or possibly three, men would be required 

 for an hour or so each morning and each afternoon. 



The importance of pilot-balloon observations over 

 the oceans is generally recognized and a full program of 

 this work should be carried out by any and every ship 

 having sufficient personnel. Though the full program has 

 been emphasized, just one series each day would be high- 

 ly valuable and the demands on personnel would be re- 

 duced considerably. 



