UPPER-WIND OBSERVATIONS OF LAST CRUISE OF CARNEGIE 



face of the sea. A shade glass, designed to reduce hori- 

 zon glare, helped on a few occasions to make the hori- 

 zon line more distinct. The eye blinder, furnished as a 

 cover for the eye not in use, reduced eye fatigue, and 

 together with the eyepiece, supported the observer's 

 head at the proper position. 



The optical system was supported over an azimuth 

 circle, which was itself carried by a base plate capable 

 of being turned in azimuth. The azimuth circle had a 

 slow-motion micrometer adjustment reading to one- 

 tenth degree, but for rapid movement when picking up a 

 balloon, this might be disengaged, and the whole head 

 rotated. 



Because the base plate was adjustable, the observer 

 was able to set the azimuth of the upper circle to read 

 on north, and thus eliminate one step in the subsequent 

 reduction of the observations. 



The index prism, carried on a movable arc, was 

 graduated to even degrees, and could be read to tenths 

 by means of a micrometer drum. 



For the purpose of making observations the theodo- 

 lite, mounted in gimbals, was set up on a heavy tripod on 

 the raised quarter-deck of the Carnegie . The legs of 

 the tripod were chained to each other and set in rubber 

 feet In order to grip firmly the deck. The theodolite had 

 attached to it, below the gimbals, a large counterweight 

 which could be made to exercise additional restoring 

 force by attaching springs. Actually the observer found 

 it most efficient to steady the theodolite by allowing the 

 counterweight to slide over, or to be lightly held in his 

 hand. 



The most important alteration in the new theodolite 

 No. 54005, which replaced Aero 1928 U.S.N. No. 15 used 

 from October 23, 1928 to August 1929, consisted in ori- 

 enting the optical system so that the observer looked 

 downward at an angle of about 45°, instead of horizontal- 

 ly, into the eyepiece. The eyepiece was placed so that 

 the observer could remain in a comfortable position 

 without the strain of continuously keeping his eye lightly 

 pressed against the moving eyepiece. Hitherto much dif- 

 ficulty had been experienced in keeping the eye uninter- 

 ruptedly on the balloon, since in the rolling and pitching 

 of the ship the eye could not quickly be brought into an 

 easy observing position. 



The azimuth circle in theodolite No. 54005 could be 

 rotated about its spindle axis and clamped in any posi- 

 tion, but the graduated base plate was not included in 

 the new design. The operator could not, without consid- 

 erable trial and error, set up theodolite No. 54005 with 

 the azimuth circle reading 0.°0 on north. The elimina- 

 tion of the graduated base plate considerably reduced 

 the manufacturing cost of the theodolite, with the single 

 disadvantage of requiring the computer to apply a con- 

 stant small correction to the observed azimuth angles. 



Hydrogen 



Hydrogen for inflating balloons was carried onboard 

 in iron cylinders having a capacity of 200 cubic feet. 

 The United States Navy supplied four cylinders at Pana- 

 ma, and subsequently replaced them, when emptied, by 

 fully charged cylinders at the naval bases at Pago Pago, 

 Honolulu, and San Francisco. 



The balloons regularly used measured about 65 cm 

 in diameter when fully inflated, so that the hydrogen in a 

 cylinder measuring 200 cubic feet would, if no gas were 



lost, have filled forty balloons. Actually, considerable 

 hydrogen was required in blowing out the long connect- 

 ing tubes, and smaller quantities were lost by valves 

 and connections, so that only fifteen balloons were filled 

 from each cylinder. 



The hydrogen cylinders were stored in the afterhold, 

 and the hydrogen passed through about 30 feet of 1/2- 

 inch rubber hose to the magnetic control room, where 

 the balloon -filling apparatus was set up. One assistant 

 stationed in the hold controlled the gas supply, and the 

 whole filling operation was completed within about a 

 minute after the connecting hose was flushed out with hy- 

 drogen. The inflation balance was supplied by the United 

 States Navy and is of the type regularly used by this 

 service. 



The balloons were inflated to ascend with an approx- 

 imate vertical velocity of 180 m per minute. To deter- 

 mine the free lift the formula employed is 



V = 72(^Vl¥-208 



where V = ascensional rate in meters per minute, S, = 

 free lift in grams, L = free lift plus weight of balloon 

 in grams. The following table, computed from the above 

 formula, gives the free lifts used. 



In accordance with the practice of the United States 

 Weather Bureau, the rate of ascent for the first minute 

 was increased 20 per cent, the second and third minutes 

 by 10 per cent, and the fourth and fifth by 5 per cent. 



Balloons 



Balloons supplied were either black or in their nat- 

 ural color, tan. Observers followed black balloons to a 

 maximum distance of 3000 m, whereas the tan bal- 

 loons were in some instances followed to a distance 

 of 25,000 m. 



From Panama to San Francisco, 6-inch balloons 

 weighing from 24 to 32 grams were used. Later on six 

 flights were made with 9-inch balloons weighing 60 to 

 75 grams. Many more would have been made with the 

 9-inch size had it not been for the impossibility of car- 

 rying the inflated balloon through the doorways leading 

 from the filling room to the quarter-deck. The only 



