摘要:

Seismic recording of the Heligoland explosion of April 18, 1947, provided important evidence on the structure of the continental shield, especially so since the region of the German bay around which most of the stations were located is well defined geologically. The depths and velocities of the three layers are discussed and comparisons are made with the interpretations of others. The velocities of the seismic waves inferred from the summarized observations are 5.4 km/sec in the upper layer (granitic), 6.18 and 6.6 km/sec in the middle layer (gabbroic), and 8.32 and 8.19 km/sec in the lowest one (peridotitic). The observational data indicate the discontinuous character of the stratification of the crust; that the granitic and gabbroic layers are not horizontal but variable in depth. When consideration is taken of possible factors involved, such as non‐uniform elastic properties of the sedimentary layer and inclination along profiles, a more uniform depth is foun

ISSN:0148-0227    

DOI:10.1029/JZ056i002p00147

年代:1951

数据来源: WILEY

摘要:

The travel‐times of longitudinal waves in sandstone were measured with high accuracy in a mine over distances of 5 to 100 meters; 0.1 mm on the recording film represented 1/50,000 second. The traveltime curves, which reflect the geological particularities in the profile, gave velocities of 4,240 and 4,100 m/sec. The frequencies of the vibrations were between 100 and 500 cycles/sec. The “frequency of the first onset” decreased with increasing distance, from 300 cycles/sec at 5 meters to 180 cycles/sec at 95 meters. Travel‐time measurements made in the laboratory with large blocks of rock gave the following average velocities: A rock‐salt block, 4,400 m/sec; two coal‐blocks, 670 and 450 m/sec; a bore‐core of coarse‐grained sandsto

ISSN:0148-0227    

DOI:10.1029/JZ056i002p00157

年代:1951

数据来源: WILEY

摘要:

The nomogram and slide‐rule, based on Napier's proportions, solve all unknowns in any spherical triangle, given three known adjacent parts. The design of a slide‐rule based on Napier's proportions has been included as a speedy means of obtaining a fairly accurate ans

ISSN:0148-0227    

DOI:10.1029/JZ056i002p00163

年代:1951

数据来源: WILEY

摘要:

The diurnal variation in the frequencies of sudden commencements of magnetic storms (SCs) and sudden impulses (SIs), defined in Section 1, is examined at six stations, Cheltenham, Tucson, San Juan, Honolulu, Huancayo, and Watheroo. The data for SCs and SIs are analysed separately for the period 1926–1946, which is common to all six stations. The results show that any local time variation in the hourly frequency of SCs seems likely to be small, and it is suggested that SCs may be more frequent in the afternoon hours, with a maximum around 13hlocal time, in agreement with the observation made by Moos from his analysis of the Bombay SCs.The hourly frequency of SIs for the six stations considered separately do not exhibit any marked local time effect. Indeed, their U.T. hourly frequencies are not greatly different from one another. When the local mean hourly frequency for the combined data at the six stations is considered, this curve shows similarities to the curve obtained by Newton in his analysis of the Greenwich records, with minima around 08hand 20hlocal time, this second minimum being much more pronounced than the Greenwich one. Much the same variation is obtained when the ratios of the observed frequencies of SIs at any one station to the greatest frequency at each U.T. are arranged according to local time and the local time mean plotted. The curve exhibits a variation which is very nearly semi‐diurnal. It is suggested that there is an essential difference between SCs and SIs in spite of the similarity of their appearance on the magnetic traces.The diurnal variations in the frequency of sudden commencements and sudden impulses with a preliminary movement in the opposite direction (SCs* and SIs*) exhibit a local time effect aad they appear to be most frequent in the afternoon. The frequency of occurrence of SCs* and SIs* may also depend on the longitude of the particular station, though this dependence may be more complex than the one suggested in [6].The curves for the annual mean number of SCs and SIs (combined) and the curve giving the annual mean sunspot numbers show striking similarit

ISSN:0148-0227    

DOI:10.1029/JZ056i002p00177

年代:1951

数据来源: WILEY

摘要:

An investigation of electromagnetic energy flow in complex media was initiated in Part I of the present series [see 1 of “References” at end of Part III], where non‐dissipative anisotropic media were considered. Before a corresponding treatment in cases of dissipative media can be carried out, it is necessary to find expressions for the velocity of a wave packet in such media. In the present paper, an intermediate step of some general applicability is taken—that of finding the group speed in a dissipative isotropic medium. It is found that the most appropriate expression for this isc/(dkn1/dk), wheren1is the real part of the refractive index at frequencykc/2π. In the course of the development, a common laxity in the formulation of the group is corrected, and also expressions are obtained which are applicable to the transmission of pulses through slabs of

ISSN:0148-0227    

DOI:10.1029/JZ056i002p00197

年代:1951

数据来源: WILEY

摘要:

This paper is the third in a series investigating electromagnetic energy flow in media of complex natures. In it, formulae are developed giving the velocity of packet propagation in dissipative anisotropic media, for both homogeneous and inhomogeneous waves.

ISSN:0148-0227    

DOI:10.1029/JZ056i002p00207

年代:1951

数据来源: WILEY

摘要:

An analysis of the mechanism ofF‐layer propagated (2F) back‐scatter is given, together with the results of multifrequeney experimental observations. It is shown that when scattering is assumed to occur at the surface of the earth (rather than in theE‐region, as some have thought) theory agrees very well with the experimental evidence. The behavior of back‐scatter for transmission near the critical frequency confirms the ground‐origin hypothesis and is particularly difficult to explain in terms ofE‐region origin. It is shown that the leading edge of the echo corresponds to energy returned from scattering centers beyond the edge of the skip‐zone. Energy from the skip‐zone edge is returned with greater delay, the time‐differential becoming larger as theF‐layer vertical‐incidence critical frequency is approached. Great care is clearly needed if meaningful skip‐distance information is to be obtained from back‐scatter observations. The rapid build‐up in echo amplitude which follows a sharply‐defined minimum time‐delay is explained in terms of a

ISSN:0148-0227    

DOI:10.1029/JZ056i002p00221

年代:1951

数据来源: WILEY

摘要:

A 205 Mc/sec signal coming from the direction of the discrete radio source Cygnus A was observed on about 200 nights during the period of October 1948 to May 1950. Individual runs were from two to ten hours duration. This paper is an account of these observations.Somewhat contrary to the results reported by Bolton and Stanley for 200 Mc/sec, the intensity of the radiation has been found to be quite variable. The mean period of the variations was about three‐quarters of a minute, which is in agreement with mean periods observed at much lower radio frequencies. Strong variations have been observed at all altitude angles of the source. The signal appears to rise above the undisturbed value much more than it falls below it, the upward excursions being several times the probable value of the undisturbed signal.A marked dependence of the variability of the signal on the altitude of the source was observed. The signal was always variable at source altitude angles less than 15°. This must mean that an important part of the variability of the radiation received from Cygnus A arises in the earth's atmosphere, presumably due to scattering by random inhomogeneities. Order of magnitude calculations indicate ionospheric scattering may be a cause of fading of incoming radiation from outer space.It is suggested that for frequencies below about 500 Mc/sec the stronger radio stars are the most suitable sources of radio frequency radiation for use in studies of the through transmission properties of the earth's atmosphere and should be of particular help in determining the physics of that part of the upper atmosphere inaccessible to normal ionospheric sounding techniqu

ISSN:0148-0227    

DOI:10.1029/JZ056i002p00239

年代:1951

数据来源: WILEY

摘要:

A new analysis of theSq‐field for the Polar Year 1932–33 indicates that the maximum daily variation ofHin equatorial regions is to be found between the magnetic and dipole equators in South America and Africa, but occurs to the south of both these equators in the Far East. It also appears that the line of maximum variation varies in position with the season, its movement being in the direction opposite to that of the

ISSN:0148-0227    

DOI:10.1029/JZ056i002p00259

年代:1951

数据来源: WILEY

摘要:

Records of magnetic field as a function of altitude have been obtained from total‐field magnetometers mounted in two Aerobee sounding rockets which were fired from the seaplane tender USSNorton Soundin March 1949. The flights were made 60 miles apart at approximately 89° west longitude, 11° south latitude, or geomagnetic longitude 341°, geomagnetic latitude −1°. The first rocket, Aerobee Round A‐10, was fired on March 17 at 17h20m90th meridian time; Round A‐11 was fired on March 22 at 11h20m90th meridian time. In Aerobee A‐10 the field decreased between 20 and 105 km in accordance with the simple dipole field, while in Aerobee A‐11 a discontinuity of 4±0.5 milligauss was observed in the altitude range of 93 to 105 km.These results (1) establish experimentally the existence of a current system in theE‐region of the ionosphere which is responsible for the diurnal variation of the earth's magnetic field at sea level; and (2) lend strong support to the dynamo theory of the daily magnetic variation which was originally proposed by Balfour St

ISSN:0148-0227    

DOI:10.1029/JZ056i002p00265

年代:1951

数据来源: WILEY