Vertical profiles of condensation nuclei in the stratosphere

An automatic condensation nuclei counter was developed for the concentration range of about 1 to 400 particles per cubic centimeter. After expansion, the water droplets are photographed when they are still suspended in the air so that the counter can be considered an absolute one. The volume in which the droplets are counted is determined by the size of the picture of the droplets as a function of their distance from the focal plane. To eliminate any effect of decreasing pressure with altitude, the cloud chamber is filled with clean air prior to expansion to about half an atmosphere above ambient pressure. This counter was used to obtain vertical profiles of condensation nuclei up to altitudes of 27 km with high altitude balloons. A total of seven profiles was obtained over a period of about one year at 47° N over the United States. Because of the restrictions in the range of the meter no data could be obtained below 5 km. The profiles show the following main features:

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   Although there are pronounced fluctuations in the individual flights the average nuclei concentration of 200 to 300/cm³ remains fairly constant from 5 km to the tropopause.     
   
   

The generation of condensation nuclei by ionising radiation

Summary The production of condensation nuclei by the irradiation of filtered nuclei-free air by X-rays, alpha particles and beta particles is described. It is found that nuclei are created in large numbers by such irradiation and that there appears to be a threshold radiation dose at which the nucleus concentration is increased by a factor of more than a hundred.The effect of varying sulphur dioxide content of the irradiated air has been investigated and for concentrations of between one and ten milligrams per cubic metre of air there is some proportionality between the sulphur dioxide content of the air and the nucleus concentration produced by a given radiation dose.It is shown, however, that sulphur dioxide cannot be exclusively responsible for the generation of condensation nuclei by irradiation of filtered air and other possible agents and mechanisms are suggested.     

Investigation of charged nuclei in the free atmosphere

Summary The results of an investigation of the time variations in the vertical distribution of charged nuclei (large ions) in the atmosphere in fair weather were presented. These experiments were carried out with instruments installed in aB-17 aircraft for measuring and recording simultaneously the concentration and mobility distribution of particles with mobility between 0.7 and 2.0×10^–2 cm²/sec-volt, electrical conductivity, temperature, pressure, humidity and air speed.Approximately 25 series of flights were carried out. Each series consisted of three to seven flights over an eight to twenty-four hour period. All flights in a given series were carried out over a fixed flight path. The average time interval between flights was four hours. On each flight constant altitude measurements were made between 700 and 15 000 feet above the surface at altitude intervals of 1000 feet.From shortly after sunrise to early afternoon all flights show a systematic increase with time in the charged nuclei concentration up to the level to which turbulent and convective mixing extends. Analysis of the meteorological data obtained simultaneously shows this is due primarily to the daily turbulent cycle.The late afternoon and night results are more complicated. It was found necessary to separate this data into two groups corresponding to periods of low and high wind velocity. During periods of low advection a systematic decrease with time was observed in the nuclei concentration from the middle of the afternoon to sunrise. Analysis indicates that these changes are the result of nuclei coagulation and subsidence in the atmosphere. Non-systematic changes with time occurred during periods of intense advection which were found to be the result of continued instability in the lowest layers of the atmosphere and to inhomogeneities in the air mass. Above the exchange layer the changes in nuclei concentration in time at a given level were found to be non-systematic.The time variations in the electrical conductivity were summarized and shown to be primarily the result of changes in the nuclei concentration. Further support for this interpretation of the results is given by the nature of the changes with time in the horizontal variations of charged nuclei, electrical conductivity and humidity.     

Charged meteoric particles as ice nuclei in the mesosphere: Part 2: A feasibility study

Recondensed meteoric material, so-called meteoric smoke, has long been considered the main candidate for condensation nuclei for mesospheric ice formation. Recently however, model studies have shown that meteoric smoke particles are transported away from the polar region, where ice phenomena such as noctilucent clouds occur, before they can grow large enough to serve as ice condensation nuclei. In the accompanying paper it is argued that charging of the meteoric smoke particles may solve this dilemma by significantly altering the efficiency of the particles as condensation nuclei. In the present paper, the feasibility of this idea is investigated more quantitatively, by analysing the time scales of processes such as charging, recombination, and particle growth. Despite large uncertainties, especially in the charging efficiency of the smallest smoke particles, we show that reasonable assumptions yield number densities of charged condensation nuclei that are consistent with what is expected for mesospheric ice phenomena.     

Le teneur de l'air en petits et gros ions radioactifs

Résumé En assimilant à des petits ions les atomes RaA provenant de la désintégration du Radon présent dans l'air, on évalue par le calcul la fraction de ces particules fixées sur les poussières et les noyaux de condensation, ainsi que leur durée de fixation.Pour vérifier ces considérations, on compte les petits et gros ions radioactifs par la méthode deZeleny, en maintenant l'électrode axiale des tubes sous tension négative, les autres particules sont fixées par captation électrostatique ou avec un filtre papier et les activités des différents échantillons sont étudiées par comptage . On trouve une concentration de l'air en petits ions RaA de 1.5·10^–4 atome par cm³. Connaissant la teneur de l'air en Radon, et en admettant que l'équilibre radioactif est atteint entre le Radon et le Radium A qui en provient, on obtient par différence les concentrations de RaA fixée sur les autres particules.

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Summary The proportion and free life time of RaA atoms arising from the radioactivity of atmospheric radon, and catched by dust particles, large ions and condensation nuclei, is evaluated, with assumption that these atoms are identical to the ordinary small ions.Experimental verification of the calculation are made by catching small and large ions withZeleny tubes, axial electrode being negatively charged. Other particles being catched with electrical precipitation and filter paper, activities of different samples are measured by counting. 1.5·10^–4 per cm³ small ions RaA concentration is found. Knowing the air radon value concentration, and with the assumption of radioactive equilibrium only between radon and RaA in free air, it is possible to evaluate the concentration of RaA catched by other particles.

     

Coefficients of volume recombination and some derived characteristics of air ions

Summary General formulas derived for the recombination and combination coefficients of charged and uncharged aerosol particles can be adapted for calculation of the recombination coefficient of small air ions by using an appropriate correction term in the exponential function and by introducingThomson's factor of enhancement of the capturing cross-section due to the central electrical forces acting between the oppositely charged ions.By using this corrected formula for the recombination coefficient, some characteristics of the ions to be recombined can be calculated when values of the recombination coefficients measured in dependence on the pressure are applied.     

Einige konstruktive Einzelheiten eines photoelektrischen Kondensationskernzählers

Zusammenfassung Konstruktionseinzelheiten eines photoelektrischen Kernzählers werden beschrieben. Die Bedienung des Zählers ist elektrifiziert und erfolgt durch elektromagnetische Ventile. Besondere Befeuchter werden benutzt. Ein Ansatz für visuelle Beobachtung der Nebelbildungserscheinungen in dem Absorptionsrohr ist eingeführt. Für Aussiebung der geladenen Kerne ist ein Kondensator angebaut, der in einfacher Weise in einen Grossionenzähler umgewandelt werden kann. Mit einer Kamera als Zusatzteil kann der Zähler in einen kombinierten photoelektrischen und photographischen Kondensationskernzähler umgewandelt werden.

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Summary Details of the construction of a photo-electric nucleus counter are described. The operation of the counter is electrified and is carried out by electromagnetic valves. Special humidifiers are used. Visual observation of the fog formation phenomena in the absorption tube is introduced. A condenser for sifting the charged nuclei is built in, which in a simple way can be converted into a counter for large ions. As an accessory a camera is provided so that the counter can be used as a combined photo-electric and photographic condensation nuclei counter.

     

The photo-electric nucleus counter as hygrometer

Summary Hygrometric measurements on room air were made with aNolan-Pollak nucleus counter from which the lining of blotting paper had been removed. The dew point can be determined from the critical overpressure for condensation on nuclei. Satisfactory agreement with the values given by a ventilated wet and dry bulb hygrometer was obtained. The correction required is small since condensation occurs on ordinary atmospheric nuclei when the temperature is brought to about 0.3°C below the dew point.

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Zusammenfassung Es wurden Feuchtigkeitsmessungen der Zimmerluft mit einemNolan-Pollak Kernzähler gemacht, in welchem das Futter aus Fliesspapier entfernt worden war. Der Taupunkt kann aus dem kritischen Ueberdruck, der für die Kondensation an den Kernen notwendig ist, bestimmt werden. Es wurde zufriedenstellende Uebereinstimmung mit den Angaben eines ventiliertenAssmann-Psychrometers gefunden. Die erforderliche Korrektur ist klein, da die Kondensation an gewöhnlichen Kernen der Luft stattfindet, wenn die Temperatur auf einen um 0.3°C verminderten Taupunkt gebracht wurde.

     

Role of condensation nuclei as carriers of radioactive particles

Summary The effect on the deposition of thoron and radon decay products of attachment to condensation nuclei is described. Methods are suggested of using these decay products as markers for condensation nuclei and comparison is made between radioactive and non radioactive determinations of the diffusion coefficients of marked nuclei. The spontaneous production of condensation nuclei by irradiation of clean air by alpha and beta particles and by X-rays is described.     

A new condensation nuclei counter with continuous oversaturation

Summary By mixing atmospheric air, saturated water vapour and hydrochloric acid a water vapour supersaturation corresponding to that in theScholz-nucleus counter is formed. The density of the fog formed is reproducibly related to the number of condensation nuclei per cm³ and can easily be measured by photocells.

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Zusammenfassung Durch Mischung von atmosphärischer Luft, gesättigtem Wasserdampf und Chlorwasserstoff entsteht eine demScholz'schen Kernzähler entsprechende Wasserdampfübersättigung. Die Dichte des entstehenden Nebels steht in reproduzierbarem Zusammenhang mit der Kondensationskernzahl pro cm³ und kann leicht mittels Fotozellen gemessen werden.

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Presented by Dozent Dr. Ing.R Mühleisen, Max-Planck-Institut für Physik der Stratosphäre,Weissenau bei Ravensburg (Federal Republic of Germany).     

A new aspect of condensation theory

This paper examines the effects of the mixing of dry air into a cloud top from the point of view of the droplet spectra. It is shown theoretically that the resulting cycling of the air up and down in the cloud, as seems to be the essential mechanism by which cumuli have been diluted to their observed liquid water mixing ratio, can double the largest drop radius and generate cloud parcels containing drops of all sizes up to this maximum. These changes in the droplet distribution with size occur by a process which is not greatly influenced by the cloud condensation nuclei or the details of droplet growth since maritime like spectra can develop in continental type cumuli. It shows that large numbers of cloud condensation nuclei should not have much effect in inhibiting the rainforming process by reducing coalescence growth. On the contrary, the controlling parameters which determine precipitation efficiency and times seem to be those which control the mixing.     

Measurement of the mobility distribution of tropospheric ions

Summary The analysis is given for an improved aspiration-type mobility chamber which suppresses the growth of boundary layers and turbulence at the electrodes by employing converging-channel geometry. The distribution of small ions in air as a function of their mobility is determined from data taken with the converging-channel chamber. The results show that the distribution of positive ions is quite stable with an average mobility of about 1.35 cm² volt^–1 sec^–1 (at STP). The negative-ion distribution is broader, less stable, and the average mobility shifts from about 2.1 to 1.7 cm² volt^–1 sec^–1 with the addition of water vapor. The effect of Aitken nuclei upon the mobility distribution is also discussed. The results are compared with previous measurements.     

On the condensation nuclei about the time of sunrise

Summary Some marked variations of the content of condensation nuclei in the air deserve to be considered individually. it is shown that by simultaneous measurements of phenomena other condensation nuclei, especially atmospheric electrical, a more complete insight into all the processes involved could be obtained, when investigating the condensation nuclei during the time about sunrise.

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Zusammenfassung Einzelne ausgeprägte Variationen des Gehaltes an Kondensantionskernen in der Luft verdienen individuell behandelt zu werden. Es wird gezeigt, dass mit gleichzeitig ausgeführten Messungen anderer, besonders luftelektrischer Erscheinungen, neben jenen der Kondensationskerne eine vollständigere Einsicht in alle in Betracht kommenden Prozesse erhalten wird, wenn die Kondensationskerne vor und nach dem Sonnenaufgang untersucht werden.

     

The mobility spectrum and the ion concentration of large ions in air mixed with N2O gas

Summary Using the divided electrode condenser it was possible to detect the large ion groups formed when small amounts of N₂O gas were mixed with atmospheric air. Eight groups appeared with mobilities ranging from 12.50×10^–4 to 0.60×10^–4 cm/sec: volt/cm. When using the whole electrode condenser the results showed an increase in the total ion concentration of these large ions when small amounts of N₂O gas were mixed with air. The results obtained in this work confirm that N₂O gas acts as a nucleus for condensation which is changed into a large ion by appropriating an electrical charge.     

Influence of sunlight on atmospheric condensation nuclei

I has been shown that irradiation of air by sun-rays leads to a formation of atmospheric condensation nuclei, as measured with the automatic nucleus counter (1).To control the influence of the material, experiments were done in a gasometer where a rubber balloon was built in, also in a metal container covered either with uviol glass or window glass, or with air in a polyethylene balloon. The same influence of sunrays was observed in each case.Similar experiments were then done with compressed air from a metal container, or with oxygen gas, nitrogen gas or nitrous oxide all from metal containers. In all cases sun-rays produced condensation nuclei; the effect was present both at 1800 m and at 270 m altitude. Diffuse sunlight with high clouds also had an effect. Infra-red radiation and mechanical shaking were without result, but ultraviolet rays from a quartz-mercury lamp increased the nucleus count of the balloon whether it contained air or one of the above-mentioned gases.As yet it has not been possible to decide the mechanism of formation of these nuclei and what their meteorological and biological role might be.The detailed paper will appear later in «Geofisica pura e applicata».     

Sur les aérosols intéressants la Météorologie

Summary The lecture is a critical survey of the studies regarding the particles in suspension in atmospheric air and which interest in the phenomenon of water vapor condensation and generally in cloud formation and in the ensuing precipitation.A part of the lecture is devoted to the manifold technics of study introduced, above all, in the last decade, in addition to the method ofAitken counting gear. It dwells particularly on the use of Millipore filter used byLodge and his collaborators for the gathering of the condensation nuclei and of the successive chemical analysis with specific reagents to make evident the nature of the nuclei.The review ends underlining the necessity that the measures of the atmospheric aerosol may be systematically carried on by the synoptical meteorological observatories and the necessity that the experiments in this field may be made with a more and more increasing care and critical mind.     

The Global Atmospheric Electrical Circuit and Climate

Evidence is emerging for physical links among clouds, global temperatures, the global atmospheric electrical circuit and cosmic ray ionisation. The global circuit extends throughout the atmosphere from the planetary surface to the lower layers of the ionosphere. Cosmic rays are the principal source of atmospheric ions away from the continental boundary layer: the ions formed permit a vertical conduction current to flow in the fair weather part of the global circuit. Through the (inverse) solar modulation of cosmic rays, the resulting columnar ionisation changes may allow the global circuit to convey a solar influence to meteorological phenomena of the lower atmosphere. Electrical effects on non-thunderstorm clouds have been proposed to occur via the ion-assisted formation of ultra-fine aerosol, which can grow to sizes able to act as cloud condensation nuclei, or through the increased ice nucleation capability of charged aerosols. Even small atmospheric electrical modulations on the aerosol size distribution can affect cloud properties and modify the radiative balance of the atmosphere, through changes communicated globally by the atmospheric electrical circuit. Despite a long history of work in related areas of geophysics, the direct and inverse relationships between the global circuit and global climate remain largely quantitatively unexplored. From reviewing atmospheric electrical measurements made over two centuries and possible paleoclimate proxies, global atmospheric electrical circuit variability should be expected on many timescales.     

Variations in atmospheric transparency under the action of galactic cosmic rays as a possible cause of their effect on the formation of cloudiness

The possible mechanism by which cosmic rays affect the formation of neutral water droplets and ice crystals in the Earth’s atmosphere has been considered. This mechanism is based on changes in atmospheric transparency and vertical temperature distribution. It has been indicated that a change in the optical thickness for visible and IR radiation by several percents, which can take place when cosmic-ray particles penetrate into the atmosphere, results in a change in the temperature vertical distribution, affecting the growth of water droplets, concentration of active condensation nuclei, and the formation of ice particles. This mechanism makes it possible to explain the correlation between the intensity of galactic cosmic rays at low altitudes and the absence of this correlation at middle altitudes.     

Some recent investigations on the nature and properties of natural and artificial freezing nuclei

Summary Working on the hypothesis that atmospheric ice-forming nuclei are largely of terrestrial origin, the nucleating ability of various types of soil particles and mineral dusts has been investigated. Of the thirty substances tested, twenty-one, mainly silicate minerals of the clay and mica groups, were found to produce ice crystals in supercooled clouds and also on supercooled soap films at temperatures of – 18° C, or above, and of these, ten were active above – 12° C. The most abundant of these is kaolinite with a threshold temperature of – 9° C. Ten natural substances, again mainly silicates, were found to become more efficient ice nuclei having once been involved in ice-crystal formation, i.e. they could be pre-activated or «trained». Thus, ice crystals grown on kaolinite nuclei, which are initially active at –9° C, when evaporated and warmed to near 0° C in a dry atmosphere, leave behind nuclei which are thereafter effective at – 4° C. Particles of montmorillonite, another important constituent of some clays, and which are initially inactive even at –25° C, may be pre-activated to serve as ice nuclei at temperatures as high as –10° C. It is suggested that although such particles can initially form ice crystals only at cirrus levels, when the ice crystals evaporate they will leave behind some «trained» nuclei which may later seed lower clouds at temperatures only a few degrees below 0° C. On this hypothesis, the fact that efficient nuclei are occasionally more abundant at higher levels would not necessarily imply that they originate from outer space. Indeed, in view of our tests on products of stony meteorites, produced both by grinding and vaporization, which show them to be ineffective at temperatures above – 17° C, it seems likely that atmospheric ice nuclei are produced mainly at the earth's surface, the clay minerals, particularly kaolinite, being a major source.Although a good deal of work has been carried out in different laboratories on the ice-nucleating ability of a wide variety of inorganic compounds, there has been little agreement in the results. Careful tests carried out in our laboratory have revealed a number of reasons for this. Spurious results may be obtained because of the presence, in the air or the chemicals, of small traces of silver or free iodine, leading to the formation of silver iodide: if all such trace impurities are removed, many of the substances that have been claimed to provide efficient ice nuclei are found to be quite ineffective. It is dangerous to infer that all twinkling particles in a water cloud are ice crystals since particles of some seeding agents glitter even at positive temperatures. The threshold temperature of a nucleant will depend upon the criterion adopted for the onset of nucleation, i.e. upon the fraction of the total number of particles of seeding agent which are activated; this, in turn, will depend upon the fraction of particles which happen to possess suitable crystallographic faces for nucleation. Much may also depend upon the manner in which the test is performed. Since some nucleating materials produce ice crystals only after a delay of 30 seconds or more, they may appear to be ineffective if tested in the transient cloud of an expansion chamber but highly effective if allowed to remain in an ice-supersaturated atmosphere for a minute or more. Again, we have found that the efficiency of some nuclei is governed by the supersaturation as well as the temperature of the environment, and the supersaturation regimes in expansion, diffusion, and mixing-cloud chamber may be widely different. Highly soluble particles, although able to act as «sublimation» nuclei in atmospheres super-saturated relative to ice but sub-saturated relative to water, on entering a water cloud go quickly into solution and lose their nucleating ability.Inorganic substances which definitely nucleate a supercooled water cloud in a mixing-cloud chamber at temperatures of –15° C and above are: AgI (–4° C), PbI₂ (–6° C), CuS (–6° C), Ag₂S (–8° C), Ag₂O (–9° C), HgI₂ (–8° C), V₂O₅ (–14° C), Cu₂I₂ (–15° C), the figures in brackets indicating the threshold temperatures at which about one particle in 10⁴ becomes active as an ice nucleus. Cadmium iodide (–12° C), ammonium fluoride (–9° C) and iodine (–14° C) are examples of salts which will act as sublimation nuclei in an ice-supersaturated atmosphere and will nucleate a supercooled soap film, but which are ineffective in a water cloud because of their solubility.Although the most efficient nucleating agents tend to be hexagonal in structure, there are some striking exceptions e.g. Ag₂S, Ag₂O, HgI₂, but in most cases, we have been able to find a low-index crystal surface on which the ice lattice could grow with a misfit of only a few per cent.In an attempt to investigate the nucleation mechanism in more detail, we have studied the growth of ice on single crystals of various nucleating agents. Perfect orientation of ice crystals has so far been observed on the basal faces of silver iodide, lead iodide, cupric sulphide, cadmium iodide, and freshly-cleaved mica, on the (001) plane of iodine, and on the (010) plane of mercuric iodide.     

Kondensationskerne im Rahmen der Luftelektrizität

Zusammenfassung Die Rolle der Kondensationskerne im atmosphärischen Geschehen wird besonders deutlich, wenn man sich vorstellt, wie sich dieses Geschehen ohne Kondensationskerne abspielen würde: Es käme dann auf der ganzen Erde nur der globale Anteil der atmosphärisch-elektrischen Erscheinungen zur Geltung während die Bindungen zum Wettergeschehen fehlen würden. Somit hängt also der gestaltende Einfluß des Wetters auf die elektrischen Vorgänge ursächlich mit dem Vorhandensein von Suspensionen bezw. Kondensationskernen zusammen.Die atmosphärisch-elektrischen Ereignisse sind zu verstehen aus dem Zusammenwirken von Generatoren und veränderlichen Schaltelementen. In beiden Gruppen spielen die Kondensationskerne eine entscheidende Rolle, wie im einzelnen gezeigt wird:Die bekannten Zusammenhänge zwischen dem luftelektrischen Potentialgefälle und der atmosphärischen Leitfähigkeit einerseits und meteorologischen Elementen (Luftkörper, Turbulenz, Austausch, Inversionen u.a.) andererseits sind aus den Wiedervereinigungsbeziehungen zwischen Kleinionen und Suspensionen zu verstehen. Sie gehören in die Gruppe der veränderlichen Schaltelemente.An einem in den letzten Jahren beobachteten Effekt (Anstieg von Potentialgefälle und Vertikalstrom nach Sonnenaufgang), der seinem jahreszeitlich verschiedenen und von Ort zu Ort wechselnden Verhalten entsprechend als Austauschwirkung zu deuten ist («Austausch-Generator»), wird nach umfangreichen Untersuchungen an einigen Stationen der Schweizer Alpen die Mitwirkung der Kondensationskerne demonstriert. Diese scheint darin zu bestehen, daß Raumladungsbildungen in der Atmosphäre je nach dem Vorhandensein von Kondensationskernen in stärkerem oder geringerem Maße gewissermaßen zeitlich fixiert werden, sodaß der zur Generatorwirkung notwendige Transport dieser Ladungen durch Kräfte nicht-elektrischer Natur quantitativ durch die Kernzahl beeinflußt wird.

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Summary The role of the condensation nuclei in the atmospheric electrical processes becomes especially evident if it is imagined how this process would take place without condensation nuclei: On the entire earth only the global atmospheric electrical phenomena would become effective, while the relations to the weather processes would not exist. Thus, the influence of the weather on the electric processes is causally related with the existence of suspensions, resp. condensation nuclei.The atmospheric electrical processes are to be interpreted from the co-operation of generators and variabile circuit elements. In both groups the condensation nuclei play an important part as is shown here in detail:The known relations between the atmospheric electrical potential gradient and the atmospheric conductivity on one hand and meteorological elements [air masses, turbulence, exchange (Austausch), inversions, etc.] on the other hand must be understood by the recombination relations between small ions and suspensions. They belong to the group of variable circuit elements.As an effect observed in recent years (increase of the potential gradientand the air-earth-current after sunrise) which, corresponding to its behaviour varying at the different seasons and from place to place, must be interpreted as exchange (Austausch) effect («Austausch-Generator»), the co-operation of condensation nuclei is demonstrated on the basis of comprehensive investigations at some stations of the Swiss Alps. This seems to exist in the fact that space charge formations in the atmosphere may be transfered into a more stable, longer lasting state by the interaction of the condensation nuclei to a greater or smaller extent so that the transport of these charges by nonelectric forces necessary for the generator effect is quantitatively influenced by the number of nuclei.