14 



OCEAN ATMOSPHERIC -ELECTRIC RESULTS 



chamber and the balancing condenser were connected to 

 their respective electrometer plates and the positions 

 again noted. If these were changed, defective insulation 

 on the battery lines was regarded as the most likely 

 cause. Differences in the zero -positions, however, of 

 about 10 per cent were tolerated in practice. 



If the differences were greater, and insulation dif- 

 ficulties were found not to be the cause, adjustment of 

 the balancing condenser became necessary. Instructions 

 for this operation were supplied in some detail. Adjust- 

 ment was not expected to be needed unless there had 

 been a creep of the adjusting screws or an unbalancing 

 caused by thermal expansion. If the outer cylinder were 

 to be removed for any reason, care was to be taken that 

 the adjustment of the inner cylinder was not changed and, 

 on replacing the outer cylinder, particular note was to be 

 taken that it was firmly seated against the shoulder of 

 the rubber insulator supporting it. In any adjustment of 

 the balancing condenser, the fine-adjustment screw (ex- 

 posed at the end of the condenser) was to be tried first. 

 If this did not provide sufficient change, the outer cylinder 

 was to be removed, and the inner cylinder screwed very 

 slightly inward or outward until the final adjustment was 

 within the range of the fine adjustment. Only a few de- 

 grees turn of the inner cylinder would be necessary to 

 produce a large difference in the fine adjustment. 



With the electrometer adjusted for equal sensitivity 

 on either side of the position taken by the fiber when the 

 battery switch was open, and with adequate insulation on 

 the battery lines, the correct adjustment of the balancing 

 condenser was that for which equal deflections to either 

 side were obtained for the two positions of the battery 

 reversing switch. These deflections usually were small; 

 for a sensitivity of ten divisions per volt they were only 

 a fraction of one division. On cruise VH no major ad- 

 justment of the balancing condenser was necessary; the 

 use of the fine-adjustment screw was sufficient on the 

 few occasions when adjustment was required. 



Chief Features of the Kolhorster Penetrating Radia- 

 tion Apparatus 5503. --This instrument consisted of an 

 ionization chamber of about four liters volume, at the 

 center of which was placed the electrometer system con- 

 sisting of two loops made from metal-coated quartz fi- 

 bers (fig. 6). These were viewed with a microscope and 

 acted in much the same way as the fibers of the bif ilar 

 electrometers. The calibrating procedure was essentially 

 the same as for the bifilar electrometers. The electrom- 

 eter system was charged either for calibrating or for 

 measuring the penetrating radiation by means of a con- 

 tact-arm located inside the chamber and connected with 

 an insulated outside binding post. This contactor was 

 operated from the outside by a magnetic device. The 

 contactor was earthed (i.e., was in contact with the walls 

 of the chamber) when in the position for observations. 

 On this account the battery was not applied except when 

 the contactor was set in the position for charging the 

 central system. The procedure for observation with this 

 instrument was: 



(a) Charge the system to a potential giving nearly a 

 full scale deflection and allow it to stand a few min- 

 utes until the charge becomes distributed over the 

 insulators of the central system 



(b) Note the positions of the fibers, and the time 



(c) About one hour later again note fiber positions and 

 the time of doing so 



The equation given earlier for calculation of R also 



applied for this instrument, 6V being the change in 

 potential represented by the change, 6, in fiber posi- 

 tions during the observed time interval, t, expressed 

 in seconds. The capacitance, C, was given by Kolhors- 

 ter as 0.374 cm and the volume, U, was 4130 cc, making 

 the working formula 



R = 630 6VT-1 



(See discussion of changes in C on page 15). 



Comparative Measurements. - -Simultaneous meas- 

 urements with two instruments so different in type as the 

 PRl and the Kolhorster were expected to be of more 

 value than a much larger mass of data obtained with a 

 single instrument, on the basis of the following consid- 

 erations. The total measured ionization in any penetrat- 

 ing radiation apparatus is produced by at least two dis- 

 tinct agencies. One of these agencies either is radio- 

 active matter in the material from which the ionization 

 chamber is made or is the natural radioactivity of that 

 material itself. The part of the ionization arising from 

 that source may be termed the residual ionization. The 

 rest of the ionization is produced by the penetrating ra- 

 diation which passes through the walls of the ionization 

 chamber and by its secondary radiation. In an air-tight 

 vessel the residual ionization may be considered con- 

 stant. It is that which would be observed if the penetrat- 

 ing radiation were cut off by surrounding the chamber 

 with a sufficient thickness of absorbing material. The 

 Kolhorster instrument was so designed that the residual 

 ionization could be determined by immersing it in a suf- 

 ficient depth of water. Dr. Kolhorster determined the 

 residual ionization of his instrument, giving the value 

 as 1.3 ion-pairs per cc per second. The residual ioniza- 

 tion for PRl, however, could not be determined by 

 immersion, and it was hoped that a satisfactory estimate 

 for it could be arrived at from comparative measure- 

 ments with the two instruments. 



Another uncertainty in the measurement of penetrat- 

 ing radiation, apart from that caused by residual ioniza- 

 tion, arises from the fact that the number of ions produced 

 in the chamber is not the same as would be produced in 

 an equal volume of air. The intensities of the rays are 

 reduced somewhat by absorption in the walls of the cham- 

 ber and the surrounding structures, but in spite of this 

 the ionization in such a chamber usually is considerably 

 more than in free air, owing to secondary radiations 

 excited in the walls of the chamber. In order to ascer- 

 tain the ratio of the observed ionization to that which 

 would be produced in free air by the same agency, the 

 so-called Eve's constant for the instrument is determined. 

 The determination of this constant for PRl was made on 

 the Carnegie at Newport News in May 1928. The result, 

 however, fell short of what was desired since it was im- 

 practicable to include the effect of masts, rigging, etc. 

 It was hoped that a fairly close estimate of the latter 

 effect could be obtained at sea by obtaining observations 

 with the Kolhorster instrument alternately in the atmos- 

 pheric-electric house and somewhere on the quarter-deck 

 well to the stern of the ship where the largest clear ex- 

 panse about the zenith could be seen. The ratio of mean 

 values of R obtained at these locations (i.e., Rq/Ri, in 

 which Ro representsquarter-deck measurements and Rj 

 the indoor measurements) would then be a "reduction 

 factor" for eliminating the effect of the ship's gear from 

 the measurements made with the Kolhorster apparatus 

 in the atmospheric-electric house. With this factor, and 

 a series of comparative measurements with PRl and the 



