INSTRUMENTS, OBSERVATIONAL PROCEDURE, AND CONSTANTS 



In accordance with the above procedure, observations 

 were made daily on cruise VII until July 28, 1929, except 

 when bad weather or other cruise programs prevented. 

 Each day three separate determinations of conductivity 

 would be made; on one day the first and third sets would 

 be measurements of positive conductivity and the second 

 set of negative, while on the following day the first and 

 third sets would be negative and the second positive. 

 Each set would require fifteen minutes or longer, depend- 

 ing on the magnitude of the conductivity. The sets were 

 so spaced and the actual manipulations of apparatus were 

 so arranged that the same observer could also make 

 measurements of ion content, penetrating radiation, and 

 nuclei content centering very closely on the average of 

 the beginning and ending times of the conductivity ob- 

 servations. 



Conductivity Recording Apparatus. --At San Francisco, 

 in August 1929, the eye-reading electrometer was re- 

 moved from the conductivity apparatus and a very satis- 

 factory recording apparatus, designed and constructed 

 by the Department staff for observations at sea, was in- 

 stalled (figs. 9, 20, 21). The shelf on the forward wall 

 of the observing cabin had originally been planned for 

 mounting the recording equipment, and the installation 

 was readily accomplished. For recording it was planned 

 that the charge acquired by the central cylinder from the 

 air stream in the air -flow tube should be allowed to leak 

 continuously through a very high resistance of about 

 10l2 ohms. With such high resistance, although the cur- 

 rent would be extremely small, the voltage drop would 

 be appreciable, of the order of a volt or two. With one 

 side of the high resistance to the fiber of a sensitive 

 unifilar electrometer and the other side to the electrom 

 eter case, a voltage drop of one or two volts would pro- 

 duce appreciable deflections of the fiber, and variations 

 in the voltage drop due to variations in conductivity 

 would cause measurable variations in the fiber deflec- 

 tion. 



Figure 9 shows that recorder as it appeared in use. 

 The electrometer, the high resistance, and other parts 

 that might be detrimentally affected by moist and salt- 

 laden air were enclosed in the metal box seen at the left. 

 Calcium chloride was placed in this box to absorb any 

 moisture which might slowly gain entrance. In figure 20 

 one side of the box is removed to show the electrometer 

 and in figure 21 the opposite side is removed to showthe 

 high resistance unit. The high resistance unit was a 

 radioactive cell of the Bronson type as modified by 

 Swann and Mauchly (7), and consisted essentially of a 

 cylindrical metal chamber about 20 cm in diameter and 

 20 cm high in which the air was made very slightly con- 

 ducting by the presence of a small amount of ionium 

 salt. 



From the metal box a lightproof tube extended to the 

 recording mechanism at the right in figure 9. Two fit- 

 tings on the lightproof tube supported glass containers 

 in which drying material was placed. A viewing hood 

 attached to the tube permitted the observer to view the 

 position of the electrometer fiber at any time. The re- 

 cording mechanism included a driving clock, a metal 

 cylinder or drum rotated by the clock, and a lightproof 

 cylindrical container in which the rotating drum was 

 enclosed. Where the lightproof tube joined the cylindri- 

 cal container a horizontal slit was provided through 

 which the image of the electrometer fiber was thrown 

 onto the photographic paper on the rotating drum. This 

 slit could be opened or closed by a simple manual 



manipulation. The drum was made to rotate once in 

 twenty-five hours, so that the photographic paper on the 

 drum would represent one day of recording of conductiv- 

 ity. Each daily record was 30 cm long and 9.5 cm wide. 

 Each hourly interval was 8.3 mm long. The scale in the 

 eyepiece of the electrometer was focused on the photo- 

 graphic paper, giving a background of lines 3.0 mm 

 apart parallel to the long dimension of the paper against 

 which to measure the fiber deflection. 



To obtain deflections representing zero conductivity 

 from which to measure the deflections obtained in regu- 

 lar recording, the sweeping potential mentioned earlier 

 was applied for a few minutes once each hour to the 

 cylinders in the upper part of the air-flow tube. The 

 potential was applied automatically by a contact device 

 fitted to the driving clock. 



Above the lightproof tube and recorder mechanism 

 was mounted the calibration apparatus by which values 

 of conductivity could be established for different de- 

 flections of the electrometer fiber. It consisted of a 

 variable cylindrical condenser, one element of which was 

 made to move by a motor at a steady rate, to give a uni- 

 form change in capacitance with time, dk/dt. Across the 

 two elements of the condenser was applied a potential, 

 V. Thus, in place of the unknown current flowing through 

 the high resistance during conductivity measurements, a 

 known current Vdk/dt was supplied by the calibration 

 apparatus. Different values of potential across the con- 

 denser gave different values of current and different de- 

 flections of the fiber. The wiring diagram of the appa- 

 ratus is shown in figure 22. 



During the three months September tc November 1929, 

 when the recording apparatus was in use, the "operating 

 potential" applied between the central cylinder and the 

 air-flow tube was maintained at 185 volts, except for the 

 brief period September 5 to 11, when various values 

 ranging from 93 to 231 volts were used at various times. 

 With the rate of air flow in the tube approximately 400 

 cm per second, and an operating potential of 185 volts, 

 ions were being drawn from a region in the air -flow tube 

 bounded by a cylindrical surface of about 4 cm radius, 

 which is only half of the radius of the air -flow tube. Ob- 

 servations for determining the sensitivity of the elec- 

 trometer were made at approximately weekly intervals 

 by applying values of 1.0, 2.0, and 3.0 volts, from a po- 

 tentiometer, between the fiber and case. A sensitivity 

 of approximately 1.3 scale divisions (4 mm) per volt was 

 consistently maintained. Calibrations of the entire ap- 

 paratus by means of the variable "calibrating condens- 

 er" were made almost daily while at sea during Septem- 

 ber 1929, and in October and November were made every 

 two or three days. Calibrations for positive and negative 

 conductivity were made on alternate occasions. The 



calibrations showed that for negative conductivity the 

 adjustment of the high resistance cell gave a constant 

 scale value of 2.1 x 10-5 esu per scale division. For 

 positive conductivity the calibrations were not linear, 

 giving greater scale values for the smaller deflections. 

 Typical values were 3.7 X 10-5 esu for 1.3 divisions and 

 3.2 X 10-5 esu for 4.5 to 5.0 divisions. The positive 

 scale values were thus more than 50 per cent greater 

 than for the negative conductivity, the difference being 

 related to the adjustment of the high resistance cell 

 and the direction of passage of current through it. 



Ion Counter l. --Ion counter 1 (ICl) used on cruises 

 IV, V, and VI, after being overhauled, provided with an 

 electric motor instead of the troublesome spring-driven 



