Die Ersatzkugel in geodätischen Berechnungen

Summary For precise geodetic computations over larger distances the reference surface of an ellipsoid of rotation should be used. However it is often replaced by a sphere of an adequate radius. The formulae are derived from figures which usually represent the conditions in a cross-section of the ellipsoid and the reference sphere through the normal plane. Equation (9) is given for the differences s of the length of the ellipse arc of the normal section and the corresponding arc of the circle with radius R. Also Eq. (19) is given for the distance d between the ellipse of the normal section and the circle (at the end point). Both equations are applied for various radii of the reference sphere. Table 1 shows the values s, Tab. 2 and Fig. 2 give the d-values for chosen lengths. It was found that especially the distance between the ellipsoid and the sphere need not always be negligible.     

On the problem of frequency calibration of induction variometers with large air-core loops

Zusammenfassung Es wird eine Methode für experimentelle Untersuchung der Frequenzkennlinien von Induktionsvariometern mit Aufnahmeschleifen nichttraditioneller Ausmasse beschrieben. Die Grundlage des beschriebenen Verfahrens bildet eine genaue Bestimmung jenes Teils des magnetischen Kraftflusses, der durch die Aufnahmeschleife durchgeht.     

Applicability of palaeomagnetism of pyrrhotite to ore-genetic studies

Pyrrhotite has never before been used in palaeomagnetic investigations, being highly anisotropic magnetically. The aim of this paper is to show that fine-grained pyrrhotite aggregates of hydrothermal origin can be used for palaeomagnetic purposes. This has been proved with polymetallic Turkak veins from Kutná Hora in Central Bohemia as an example. It can be assumed that other localities with occurrence of hydrothermal pyrrhotite aggregates which contain directionless, uniformly scattered pyrrhotite grains and therefore forming a magnetically isotropic medium may be suitable for palaeomagnetic studies.

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Zusammenfassung Pyrrhotin, mit einem hohen Grad magnetischer Anisotropie, ist bisher für die paläomagnetische Datierung unbeachtet geblieben. Diese Arbeit will zeigen, daß feinkörnige Pyrrhotinaggregate hydrothermalen Ursprungs für paläomagnetische Untersuchungen geeignet sind, was am Beispiel polymetallischer Gänge von Turkak in Kutná Hora in Zentralböhmen dargestellt wird. Es ist anzunehmen, daß auch andere Vorkommen hydrothermaler Pyrrhotinaggregate in denen regelmäßig verteilte Körner richtungslos orientiert vorliegen und so ein magnetisch isotropes Medium bilden, sich für paläomagnetische Untersuchungen eignen.

     

Dynamic manifestations of the geomagnetic field in the Quaternary continental sediments of Czechoslovakia

Summary The paper brings a brief geological asessment of the sedimentational cycles, analyses the methods of collection and investigation of samples and the representativeness of the results obtained. Problems of magnetic cleaning and the types of demagnetization curves investigated are discussed. The continuous nature of the variations of the magnetic declination, inclination and remanent magnetization, determined by palaeomagnetic investigation of Quaternary sediments, is also discussed. The conclusion contains the principal facts about the dynamics of the geomagnetic field in the Quaternary and points out the possibility of applying them to the theory of the geomagnetic field, as well as to geological correlations.     

Structural control and history of origin of hydrothermal metallogeny in western Cuba

The main structural-lithological factors responsible for the localization of hydrothermal mineralization on a regional, as well as on a local scale in the metallogenic province of western Cuba are summarized. The supply function of regional fault structures extending towards depth is emphasized and light is thrown on the localization of hydrothermal veins in fissures of the folded San Cayetano Formation. Stress has been laid on the genetic and chronological independence of pyrite bodies and hydrothermal veins. Six mineralization stages have been defined and their general succession in the metallogenic area under consideration has been determined.

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Resumen Los factores principales litológico-estructurales, que causan la predisposición de la localización de los yacimientos hidrotermales en las dimensiones regionales y locales en la region de Cuba occidental, están sumarizados. La importancia de las dislocaciones regionales para el aporte de las soluciones hidrotermales está subrayada y las causas de la localización de las vetas hidrotermales en las ac-grietas de la formacion plegada de San Cayetano están aclaradas. La independencia genética y cronológica de los cuerpos de pirita y de las vetas hidrotermales polimetálicas está discutida. Seis estados de la mineralización hidrotermal están identificados y la succesión de la validez general para toda la region metalogenética de Cuba occidental está construida.

     

The Effect of Geomagnetic and Solar Activity on the Distribution of Controlling Pressure Formations in the Northern Hemisphere in Winter

The distribution of controlling pressure formations, occurring in the Northern Hemisphere during the winters (January and February) of the years 1952 – 1996, has been analysed. It was found that the deepening of the Icelandic and Aleutian pressure lows is connected not only with a particular QBO phase and level of geomagnetic activity (Bochníek et al., 1999) but also with a particular level of solar activity.     

Seeing Conditions at Sutherland. Results of the 1992/93 seeing campaign

In order to decide whether the seeing conditions at SAAO/Sutherland justify the erection of a 3.5 m telescope and also to compare Sutherland with the Gamsberg/Namibia site, a seeing campaign covering 15 months has been carried out. For direct comparison with the results of the seeing campaign at Gamsberg twenty years before the same QUESTAR telescope was employed. The seeing is determined by the scattering of the star-trail exposed on a film in the focal plane of the telescope. The campaign commenced in February 1992. Up to May 1993, data for 204 nights, that is 47.3% of the total number of nights, were collected. Due to wind speeds above 30 km h^-1, 25 out of the 204 nights were not considered in the final reduction. The useful 179 nights are evenly distributed over the campaign period. The median seeing value for the whole period is = 0.52. There are differences during the year: the best season gives = 0.42, the worst = 0.67. Each night was divided into three intervals, although data for each of the three intervals were not always available. Generally, there is an improvement in the seeing during the course of a night. The results are compared to the seeing values of Gamsberg/Namibia and ESO/La Silla.     

The period of rotation and the photoelectric lightcurve of the minor planet 79 eurynome

The minor planet 79 Eurynome was observed during the 1974 opposition for four nights in November, using a photoelectric photometer attached to the 60 cm telescope at the Observatoire de Haute Provence, France. A synodic period of P_syn = 5^h 58^m46^s ± 6^s m.e. was derived. The total amplitude of the lightcurve is only 0.05 mag. The lightcurve shows a double maximum and double minimum. Both minima appear to be at the same level. Observations were carried out in an instrumental filter system (UBV)' Results are shown only for V′, but U′ and B′ measurements supplement the conclusions concerning the rotation. The phase angle α, covered by the observations, ranges from 3 to 5°. The present results for 79 Eurynome rule out the longer period of 0^d.49830 derived by F. Scaltriti and V. Zappalà in favor of their possible period of 0^d.24915.