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The last few years have seen great advances in the instrumentation used to obtain X-ray spectra of the Sun. These new observations reveal a wealth of multiplet structure containing many lines which allow us to understand more of the nature of the coronal plasma. Three areas of interest are examined. (1) The temperature sensitive satellite lines to helium —like resonance lines. (2) The strong lines of neon —like iron, Fexvii. (3) The combination of high spectral and high spatial resolution (Skylab) observations.

Measurements of the solar X-ray spectrum between 3 A and 15 A are reported. They were made with two slitless Bragg crystal spectrometers flown on a Sun-pointed Skylark rocket on 8 August, 1967. The use of a beryl crystal has provided higher spectral resolution than hitherto in the spectral range 12 A and 15 A leading, in particular, to a revised identification of the strong line at 13.71 A. Separate components of the stronger emission lines are clearly seen from each of three coronal active regions which may be identified on radio and X-ray spectroheliograms. The absolute line fluxes are used to determine a model for each active region in terms of the differential emission measure as a function of electron temperature. Emission lines due to the transition 1s 2 1 S 0 – 1s2s 3 S 1 in several helium-like ions are identified and values of the local electron density derived from measurement of the line flux in these ions.

Observations of solar active regions by a grazing incidence X-ray telescope on board OSO-5 are reported. The evolution of the hot, coronal components of active regions have been studied during successive rotations across the solar disc. In particular, it is found that the X-ray emission is very dependent on the photospheric magnetic field. Models of active regions are constructed as a function of the underlying magnetic field.

The X-ray emission of individual solar active regions is found from OSO-5 data to vary on three main timescales. Flare associated events typically last for times of minutes to an hour. Events lasting several hours, with several peaks in the X-ray emission, are accompanied by a simplification in the magnetic field, and often mark a turning point in the life of the region. Smooth changes over periods of several days are associated with the general development of a region. Examples of these last two variations are presented.

It has been suggested to me that a brief résumé of an illustrated article published last year in the Zeitschrift der deutschen geologischen Gesellschaft might be of general interest. The article in question embodies a piece of research work undertaken at the instance and under the direction of Professor Kayser, of Marburg, who during the Summer of 1900 observed in the neighbourhood of Königsberg, not far from Giessen, a bed of rock differing palæontologically and petrographically from the surrounding Culm slate. The rock, a slaty breccia with a considerable limestone content, furnished even on cursory examination a fauna deviating considerably from that generally associated with the Culm. Type-fossils of the Posidonia Slates (the “Culm of Herborn”), such as Posidonia Becheri, Orthoceras striolatum, and Goniatites crenistria, were not met with, but on the other hand Crinoid stems together with fragments of large Producti and of Trilobites of the genua Phillipsia appeared plentiful.

The temperature and density structure of a ‘typical’ coronal active region is deduced from X-ray observations of several active regions. Observations of the limb transits of three regions from OSO-5 indicate that the X-ray emission originates between 2 × 104 km and 1.5 × 105 km. An emission measure-temperature distribution is deduced from high resolution X-ray spectra obtained with a rocket observation of two similar regions. These observations are combined to give a model of a ‘typical’ active region, the temperature varying from 2 to 6 × 106 K with corresponding densities between 2 × 109 and 1010 cms−3.

A grazing incidence X-ray telescope for the study of the spatial and temporal variation of solar X-radiation in the region 0.8 to 1.6 nm, with proportional counters and pulse height wavelength discrimination, is described in some detail. An accompanying slit system covering the 0.3 to 0.9 nm region provides a more rapid coverage of flares than the spacecraft raster period would otherwise allow. Results are given illustrating the types of data being received from this instrument, which has been operating correctly for 18 months.

Observations of a number of supernova remnants have been carried out with the low energy X-ray telescope on the Copernicus satellite. Data are presented on the X-ray structure of the remnants Cassiopeia A and Puppis-A. Marginal detections or new upper limits are reported for the remnants IC443, DR4, MSH15-52A, Downes 83, Downes 84 and 3C392.

IN a previous communication1 observations of satellite lines to the resonance lines of several helium-like ions of the form ls2.n/-ls2p.nl were reported in the solar X-ray spectrum. It was shown that for a non-flaring active region the dominant mechanism for populating the doubly excited upper levels of these transitions was that of dielectronic recombination. Further measurements of the He-like lines have since been made with a new design of Bragg crystal spectrometer, which has a greater sensitivity and resolution. The new instrument contained three crystals each with an effective area of 50 cm2 and a field of view of 3 arc min FWHM. The Bragg angle readout was with a 14-bit shaft encoder, allowing the accurate determination of absolute wavelengths.

This paper describes the analysis of soft X-ray spectra of solar active regions observed on a Skylark sounding rocket flight. The experiment was launched from Woomera, South Australia, at 0535 UT on 26th November 1973. The payload consisted of 3 plane scanning Bragg crystal spectrometers, covering the wavelength range 4 to 23 A, and collimated to 3 arc min FWHM. The instrument was the same as that used by Parkinson (1972, 1973). The launch was part of a collaborative observing program with American Science & Engineering who obtained X-ray photographs of the Sun with the S0-54 ATM X-ray telescope, simultaneously with the Leicester observations. We report preliminary results for McMath region 12624 (S10 W28). This region was observed about 60 min after the peak of an importance —N, class CO flare.

Observations of a number of supernova remnants have been carried out with the low energy X-ray telescope on the Copernicus satellite. Data are presented on the X-ray structure of the remnants Cassiopeia A and Puppis-A. Marginal detections or new upper limits are reported for the remnants IC443, DR4, MSH15–52A, Downes 83, Downes 84 and 3C392.

Read before the Sacramento Society for Medical Improvement, Dec. 16, 1884. To propose a new surgical pocket case may seem a very unnecessary proceeding, yet a glance at the catalogue of any large instrument maker shows that the best form has so far not been attained, for in no class of appliances, except perhaps the obstetric forceps, is the variety as great. Its name implies that it contains such instruments as may be required in minor surgery, arranged in the smallest bulk, so as to be readily carried with the minimum of inconvenience. In looking over the different models one must be struck by their singular unfitness for this object. The instruments are often clumsy and ill adapted for their purposes, the knives arranged in combinations dissimilar in ability, and articles are included which in practice are almost useless. No better instance of this can be cited than the British

SummaryThis paper describes the analysis of soft X-ray spectra of solar active regions observed on a Skylark sounding rocket flight. The experiment was launched from Woomera, South Australia, at 0535 UT on 26th November 1973. The payload consisted of 3 plane scanning Bragg crystal spectrometers, covering the wavelength range 4 to 23 Å, and collimated to 3 arc min FWHM. The instrument was the same as that used by Parkinson (1972, 1973). The launch was part of a collaborative observing program with American Science & Engineering who obtained X-ray photographs of the Sun with the S0-54 ATM X-ray telescope, simultaneously with the Leicester observations. We report preliminary results for McMath region 12624 (S10 W28). This region was observed about 60 min after the peak of an importance – N, class CO flare.

NEW solar X-ray spectra have been obtained from four Bragg crystal spectrometers launched on a Skylark rocket pointing towards the Sun at 11.13 UT on December 6, 1970, from Sardinia, Italy. Each spectrometer was collimated to 4 arcmin FWHM and pointed at an active region near N20 W40 (McMath region 11060). Spectra between 4.0 and 22.5 A were obtained and will be reported in detail in a later article. The use of a collimator to limit the field of view has considerably increased the spectral clarity, compared with earlier observations, by excluding the contributions from other active regions1. A direct consequence is that several weak satellite lines have been observed for the first time in the solar X-ray spectrum. The proximity of these lines to the He-like 1s2−1s2p lines indicates they are all transitions of the type 1s2. nl−1s2p.nl.