n. INSTRUMENTS, OBSERVATIONAL PROCEDURE, AND CONSTANTS 



Among the chief difficulties associated with atmos- 

 pheric-electric work at sea is that of overcoming the 

 effect of the ship's motion on the measuring instruments 

 and of securing good insulation of the instruments. For 

 satisfactory observing with the ship's motion, bifilar and 

 unitilar electrometers were adopted on early cruises of 

 the Carnegie (1) and their use was continued on cruise 

 VII. Bifilar electrometers of WuU's design, as modified 

 by the Department of Terrestrial Magnetism, were used 

 and unifilar electrometers of the Einthoventype as mod- 

 ified by WuU . In both types of electrometers very fine 

 fibers spun from quartz, made conducting by a very thin 

 coating of gold or platinum, constitute the measuring 

 elements. The fibers, of the thickness of fine spider- 

 threads, are attached at their upper ends to the amber- 

 insulated main terminal of the electrometer and at their 

 lower ends to a bow or circle also made of a quartz fi- 

 ber but not coated. The bow or circle maintains tension 

 on the fiber system at all times. The amber and quartz 

 mountings provide satisfactory insulation for the fibers. 



In the bifilar instrument the two fibers are attached 

 at the same point both at top and bottom. When the fi- 

 bers are electrically charged they repel each other, and 

 the resulting deflection can be read with a microscope 

 suitably mounted in relation to the fibers and containing 

 a graduated scale in the eyepiece. This type of instru- 

 ment is useful where a sensitivity no greater than one- 

 half to one division per volt is required. The fibers are 

 mounted inside a housing consisting of an inner and an 

 outer case. The inner case is insulated from the outer 

 as well as from the fiber system, so that by raising or 

 lowering its potential, by means of batteries, the read- 

 ings of the instrument can be brought to any desired part 

 of the scale in the eyepiece. The auxiliary potential on 

 the inner case also permits the instrument to be used for 

 any desired range of potential. 



In the unifilar electrometer, instead of an inner 

 case, two insulated metal plates are mounted, one on 

 each side of the fiber, with their planes parallel to each 

 other and to the quartz fiber. With the case of the in- 

 strument earthed, and the plates charged to say +100 

 volts and -100 volts respectively, or any other conven- 

 ient amount, any charges communicated to the fiber will 

 cause it to be deflected. The sensitivity of the electrom- 

 eter may be altered either by changing the field between 

 the plates or by changing the tension on the fiber. The 

 latter may be accomplished by adjusting the position of 

 the support of the bow or circle at the lower end of the 

 fiber. 



Batteries used for supplying potentials to the inner 

 cases of bifilar electrometers or to the plates of unifilar 

 Instruments for the eatly part of cruise vn, were of the 

 silver chloride type, in banks of 100 cells each, and giv- 

 ing approximately 100 volts potential, but for the greater 

 part of the cruise commercial 45-volt "B" batteries 

 gave very satisfactory service. Both tjrpes of batteries 

 were protected as well as possible from the moist sea 

 air and the spray by being installed in closed cabinets in 

 the atmospheric-electric observing cabin, on shelves be- 

 low deck, or in other closed compartments, suitable con- 

 necting wires being brought to the instruments from 

 these locations. 



The observing cabin on cruise VU was the same size 

 and shape as on previous cruises and was located in the 

 same place, although it was rebuilt just before cruise 

 vn was begun. It stood between the mainmast and the 

 after magnetic dome and was midway between the port 

 and starboard rails. Thus it was not far forward of the 

 quarter-deck (figs. 1, 2). The rebuilt cabin was equipped 

 with convenient electric outlets for obtaining 110-volt 

 direct current for lights and motors from the ship's 

 power plant in the engine room. The cabin also con- 

 tained shelves, storage compartments, and work tables 

 or benches. 



Within the cabin there were permanently mounted 

 four atmospheric-electric instruments, together with 

 numerous items of auxiliary equipment including control 

 and calibrating apparatus. Along the port wall, in gim- 

 bals attached to the ceiling of the cabin, were disposed 

 ion counter 1 (ICl), penetrating radiation apparatus 1 

 (PRl), and radioactive content apparatus 4 (RCA4). 

 These pieces of apparatus were designed and constructed 

 by the Department for use on cruises IV, V, and VI but 

 were overhauled, improved in some respects, and put in 

 good working condition before installation for cruise VII 

 (figs. 3, 4, 5). Along the after and starboard walls were 

 work tables and benches. At Hamburg, Germany, in 

 July 1928, a portable penetrating radiation apparatus was 

 added to the atmospheric-electric equipment, designated 

 as Kolhorster apparatus 5503. When used for simul- 

 taneous observations with PRl, it was placed on a sheU 

 in the atmospheric-electric cabin just beneath PRl (fig. 

 6). 



On the forward wall of the cabin was a shelf for the 

 conductivity apparatus. The conductivity apparatus was 

 new and arranged otherwise for cruise VII than for pre- 

 vious cruises. On previous cruises the tube through 

 which the sample of air was drawn for the conductivity 

 measurements had been located horizontally just above 

 the roof of the cabin near the after end, with the elec- 

 trometer located centrally below it within the cabin, sup- 

 ported in a gimbal mounted on the ceiling of the cabin. A 

 large wooden box covered the tube when the apparatus 

 was not in use. For cruise Vn a vertical air -flow tube 

 was adopted, standing at the port end of the shelf on the 

 forward wall of the cabin and extending through the roof, 

 and capped with a conical hood at a height of approxi- 

 mately one meter (figs. 7, 8). The new apparatus was 

 designated 8A (CA8A), and was planned for continuous 

 registration of conductivity. The recording equipment 

 was not completed by May 1928, however, and only the 

 alr-flowtube and central cylinder and their appurtenances 

 were installed at the beginning of the cruise. An eye- 

 reading electrometer was utilized in place of the uncom- 

 pleted recording equipment for measuring conductivity in 

 the same manner as on previous cruises. 



Figure 7 shows the eye-reading electrometer fas- 

 tened to the shelf and making connection to the insulated 

 central cylinder of the air -flow system through a small 

 connecting tube. Below the shelf the vertical tube was 

 connected to a horizontal duct running along the port wall, 

 and at an aperture in the after wall at the end of the duct 

 a motor-driven fan was mounted to draw the air through 

 the air-flow system. The eye-reading electrometer was 



