In a joint project of the Department of Terrestrial Magnetism, Carnegie Institution of Washington, and the United States Air Force, acceptable electric surveys were made over the tops of 21 thunderstorms in the central United States during July to October, 1948. The purpose of the project was to ascertain whether thunderstorms supply negative electricity to the earth at the rate required to maintain the general negative electrification (negative surface charge) which is almost invariably observed during fair weather. A pressurized aircraft (B‐29), equipped with instruments for registering the data required to determine the electrical conductivity of air and the vertical component of electrical field strength, as well as auxiliary data, was used. Each traverse of a survey was aimed over the center of the region which returned strong radar echoes. A “profile” of vertical current density could be constructed from the data obtained on each traverse. The distribution of current density obtained in this way is the basis for estimating the total average current during a survey of a given storm. For one storm a current of 6.5 amp was estimated, but all other values are much smaller, ranging from 0 to 1.4 amp. The mean of all values is 0.8 amp; omitting the extremely large value it is 0.5 amp. The direction of the current, in the conventional sense, is upward in all cases, thus indicating that the net charge transported from thunderstorms to earth is negative. This result supports the view that thunderstorms do maintain the general negative charge of the earth. The average current (I) derived from these surveys is of the right magnitude if the world population of thunderstorms (N) is such that IN is equal to the total electric conduction current for all fair‐weather areas, namely, about 1800 amp—a value derived from numerous observations made in representative areas of the earth. For I equal to 0.8 or 0.5 amp, N should equal 2200 or 3600, respectively. C. E. P. Brooks estimated 1800 for the average thunderstorm population, but this estimate doubtless tends to be too small for the comparison in hand here because, being based on reports of thundery days noted at the meteorological stations of the world, the occurrence of more than one thunderstorm on any one day is not taken into account and no distinction is made between a simple thunderstorm with only one center (or “cell”) of electric activity and a complex storm which has two or more such centers. It, therefore, seems likely that an average value of I as small as 0.5 amp, or perhaps smaller, is adequate. The conclusion is that the results of this project corroborate other evidence which indicates that thunderstorms do maintain the universal negative electrification of the earth.
By means of automatic recorders, the small-ion and large-ion content of the atmosphere at ¾Vashington, D.C., have been secured. The number of large-ions have been continuously recorded over a period of nineteen months and the small-ions over a period of twelve months. Curves of diurnal variation of large ions and of small ions for the various months of the year are drawn. During the cold season of the year, the large ions pass through maxima in the morning and in the evening. During the warm season, only the evening maximum is present which shows a seasonal variation in time of occurrence. The small-ion variation through the day is more or less reciprocal to the large-ion variation, but is considerably smaller when regarded on a percentage basis. This is largely attributable to the fact that a portion of the current in the small-ion counter is contributed by intermediate ions present in the atmosphere.The large ions and relative humidity vary directly during the cold season and in an inverse manner during the warm season. This change in character from one season to another will be a contributing factor to the daily and yearly changes that occur. The mobility of the large ions, as determined in this investigation, is noticeably greater than that ascribed to them by Longerin, thus indicating that the ions in the two places are not identical in size, unless the difference may be attributed to a difference in experimental conditions.
In July and August, 1931, observations were made on the total and uncharged condensation‐nuclei in the free atmosphere on the grounds of the Department of Terrestrial Magnetism of the Carnegie Institution of Washington, in northwest Washington. The nuclei were measured before and after passing through a large‐ion counter between the tubes of which sufficient potential was applied (about 900 volts) to remove all charged nuclei with mobility of 1/3000 cm per second per volt per cm. From 21 sets of measurements, the ratio of uncharged to total nuclei (N0/NA) is found (after applying corrections for loss of nuclei while passing through the apparatus) to be 0.66, the mean value of N0 being 6,300 and the computed value of NA being 9,500. With potentials of 535, 890, and 1890 volts interchanged on the large‐ion tubes, practically no change occurred in No/NA, showing the mobility of the large ion to be not less than 1/1700 cm per second per volt per cm. In October and November, 1931, 77 measurements were made with the large‐ion counter on the number of electronic charges of one sign (positive and negative alternately) per cc in the atmosphere, simultaneously with measurements of total and uncharged nuclei. Small ions were removed from the air entering the large‐ion counter by a small‐ion counter attached to the intake. From these data N0/NA is 0.72, N±/NA is 0.14, N0/N± is 5.8 and the charge per large ion 1.10, the last figure being in good support of the generally accepted view that each large ion carries only one electronic charge. It is seen that NA = N0 + 2N±. The values of N0 and NA are more than double those found in July and August, being 15,000 and 21,000 nuclei per cc, respectively. These results are compared with the work of J. J. and P. J. Nolan, Scholz, Hess, and Israël, and evidence is found for believing that the ratio N0/NA increases in magnitude with increasing nuclei‐content of the air. A quite different analysis of the data obtained in October and November than was made for the above results is undertaken on the basis that N±/NA is not 0.14 but has instead two values, since 23 individual values fall closely around 0.20 and the remaining 54 around 0.10. The immediate conclusion is that the nuclei are at times doubly charged. From this point of view, the data are retabulated and re‐examined and it is found that the results do not show any inconsistencies which would preclude the possibility that doubly‐charged large ions were present almost exclusively on certain occasions and singly‐charged ones almost exclusive on other occasions during the observations here discussed.
This article introduces a special volume of Advances in Archaeological Practice dedicated to the interpretation and presentation of archaeology. It provides an overview of several essays that came out of a session at the European Association of Archaeology Conference in 2017, which focused upon how interpretation can be implemented within daily practices of (cultural resource management) archaeology in a way that provides heritage value. We bring the arguments together into a call for a creative, interpretive archaeology that does not take compliance or academic publications as its end goal but will speak to a far wider range of audiences through the development and presentation of stories and narratives that truly engage and inspire people. We argue that this can be achieved by implementing “emotion design” methods that dynamically differentiate between information, message, emotion, and media, by working closely together with creatives, interpretive experts, communities, and partners and, ultimately, by integrating interpretation firmly at the core of planning processes, archaeological workflows, and our daily practices.
Gorée Island is Senegal's first site on the UNESCO World Heritage List. It is associated with the infamous Atlantic slave trade, and over the past few decades, Gorée has become a prime destination for global tourism, particularly for the African diaspora from the New World but also for many Europeans and African nationals. Today, Gorée is a forum where different stakeholders battle over the role, place, and significance of the island in the Atlantic slave trade and its enduring legacies in the present. While Gorée owes much of its reputation to its heritage, including architecture, archaeology, and monuments, recent controversies over site preservation and policy compliance raised questions about heritage presentation and consumption. This article analyzes stakeholders’ attitudes toward archaeology and heritage to gain insights on how they are presented and consumed by different stakeholders and eventually destroyed by them as well. The discussion shows ambiguous attitudes toward site presentation and preservation, which might be linked either to stakeholders’ subjectivities or hypocrisy or to poor and uncoordinated communication strategies by heritage professionals.
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