12 



OCEAN ATMOSPHERIC-ELECTRIC RESULTS 



potential gradient of the atmosphere is greater and the 

 conductivity less than when they are few. The particles 

 acquire and lose charge through combining with small 

 ions and with each other, and on any given occasion some 

 will be charged positively, some negatively, and others 

 will be imcharged. It is a matter of considerable impor- 

 tance to determine what part these particles play in the 

 Ion equilibrium of the atmosphere. 



Aitken called the particles "dust" particles and his 

 instrument the dust counter, but, since his particles are 

 not dust particles as we now know them, to avoid confu- 

 sion they are called condensation nuclei and his small, 

 portable counter the Aitken pocket nuclei counter. Fig- 

 ure 13 is a view of the Aitken pocket nuclei counter and 

 details are shown in the drawings in figure 24. A shal- 

 low circular receiver, R, connects through a three-way 

 cock, K, with a piston chamber, P, when the cock is set 

 as shown. The cock, K, when turned 90°, connects the 

 receiver to the outer air, while at the same time the 

 piston chamber is, by a separate orifice, also connected 

 to the outer air. The volume of the receiver is a few 

 cubic centimeters and the piston chamber about one- 

 third that of the receiver when the piston is down at full 

 stroke. Hence the air in the receiver may be expanded 

 about 30 per cent by a full piston stroke. 



The air in the receiver is kept saturated by a mois- 

 tened disc of blotting paper, mounted on a loose disc 

 within the receiver. When the counter is shaken, the 

 disc mixes the air. In the bottom of the receiver is a 

 glass window divided into millimeter squares for a 

 counting stage, and on the receiver cover is mounted an 

 eyepiece, M. Light is directed into the receiver by an 

 adjustable mirror mounted below the receiver on the 

 piston tube and so designed as to give black background 

 illumination. To move the piston the operator uses the 

 knurled collar which slides on the tube, G. When the 

 piston is pulled down sharply, moisture in the receiver 

 will condense on the nuclei present and make the latter 

 readily visible through the low power eyepiece as they 

 fall On the counting stage. It is always assumed that 

 nuclei once deposited are never returned to the air and 

 recounted, and the functioning of the counter indicates 

 that such an assumption is justified. 



On the side of the tube, G, are markings of 1/5, l/lO, 

 1/20, and 1/50 which are used when introducing different 

 proportions of impure air into the counter for testing. 

 Aitken arranged the markings to be so placed on the tube 

 that when the knurled collar is set with its bottom edge 

 coincident with one of them, impure air is introduced in 

 such quantity that when it is mixedwiththe pure air in the 

 receiver and expanded by a full piston stroke, there will 

 be in the receiver that proportion of impure air speci- 

 fied by the marking. An equation for this was given by 

 Wait (10) in connection with his study of several counters 

 made after Aitken's design, as follows. If Vr is the vol- 

 ume of the receiver, Vx the volume of the piston tube 

 with the piston down at full stroke, and Vg the volume of 

 the piston tube above the piston head for any marking 

 1/S, then [(Vr + Vx)/Vr]-f(Vr + Vs)/Vs] = S. Aitken also 

 arranged the height of the receiver above the counting 

 stage to be one cm, and by counting particles falling on 

 a mm square his sampling was made from a volume of 

 0.01 cc in the receiver, necessitating introduction of a 

 factor K = 100 to obtain particles per cubic centimeter. 

 Seven instruments of the Aitken design made in Ger- 

 many and the United States were found by Wait to have 

 dimensions different from those of the original Aitken 



instrument and also to have the markings on the tube, 

 G, improperly placed. In particular, the height above ' 

 the counting stage was not one cm, thus affecting the fac- 

 tor, K. The two instruments used on cruise Vn (count- 

 ers 4 and 5) were of this group and for these the product 

 SK, instead of being 500 for l/s setting, 1000 for l/lO 

 and so on, had values as follows. ' 



Setting 



Product SK 



Counter 4 Counter 5 



The use of the counter involves several systematic 

 operations including initially clearing all nuclei from the 

 receiver, next introducing a certain proportion of outside 

 air, then mixing the air thoroughly, and finally expanding 

 it enough times to insure the deposit of all nuclei from 

 the air, at the same time counting all the droplets that 

 fall on a chosen square in all the expansions. 



To clear all nuclei from the receiver, the cock. A, 

 is closed and cock, K, set as shown in figures 13 and 24, 

 after which repeated strokes of the piston are made until 

 no more particles fall on the counting stage. Sometimes 

 the repeated strokes of the piston will build up pressure 

 in the receiver, apparently because on the downstroke of 

 the piston small quantities of air somehow enter through 

 interstices too small to admit nuclei as well, and this 

 pressure must be relieved or the subsequent nuclei meas- 

 urements will be erroneous. Therefore, after the several 

 strokes to clear the receiver have been made, the piston 

 is left at its highest position and the cock, K, turned so 

 as to connect the receiver with the outside air, to equal- 

 ize the pressure inside and out. The cock, K, then is 

 promptly restored to its initial position. Then the piston 

 is set to one of the settings on tube, G, and the cock, K, 

 turned 90°, permitting outside air to enter the receiver 

 to equalize the pressure inside and outside. At the same 

 turning of the cock, the piston chamber is connected to 

 the outside air and next it is exhausted into the outside 

 air by bringing the piston to its highest position. The 

 cock, K, then is restored to its first position, connecting 

 the receiver with the piston chamber. The counter now 

 is shaken to stir the air in the receiver, the mirror ad- 

 justed for the best illumination of the counting stage, and 

 the piston smartly pulled down for its full stroke. With 

 the expansion thus produced, droplets will appear and 

 fall to the stage, where the number falling on a given 

 square must be counted. The counting must be done very 

 quickly as the droplets evaporate in a few seconds. 



The piston is then returned to its highest position, 

 after which a second expansion is made. The droplets 

 in general will be fewer on this expansion, and by the 

 fifth or sixth expansion only one or none at all may fall 

 if the counter is not leaking. Usually no particles are 

 left to fall after the fifth or sixth expansion. 



For a satisfactory set of observations ten repetitions 

 of the above manipulations are generally made. 



If for a given setting of the piston more than ten 

 droplets are deposited on the chosen square on the first 

 expansion, the observation should be discarded, the re- 

 ceiver cleared of nuclei, and a new setting of the piston, 

 representing a smaller proportion of polluted air, should 

 be adopted for the particular occasion. To count more 



