R. Ananthakrishnan

Distribution of heights of prominences

Study of the frequency distribution of heights of nearly 50000 prominences observed on K Spectro-heliograms during a complete solar cycle shows a nearly exponential decrease of frequency with increasing height between 20″ and 220″ of height above the chromosphere.

Prominence activity (1905–1952)

SummaryThe paper illustrates with a series of diagrams the variation of prominence activity during the period 1905 to 1952 based on the prominence statistics collected at the Kodaikanal Observatory. The main features of prominence activity brought out by these diagrams are briefly discussed.

Relation between Wind and Pressure at Low Latitudes

INVESTIGATIONS of the relation between wind and pressure in the extra-tropical latitudes show that in the case of large-scale flow the actual wind does not deviate much from the geostrophic wind. Similar investigations at low latitudes have been few. It is generally realized that on account of the small value of the Coriolis parameter at low latitudes one should be cautious in extending considerations based on quasi-geostrophic balance to such latitudes.

Spectrophotometric study of sunspots

SummaryAfter a brief review of some of the earlier work on sunspots the experimental technique employed for the spectrophotometry of sunspots and the results obtained in the case of 5 spots are described. In the case of one of the spots studied on 1951 May 13, the intensity ratio umbra/photosphere decreased from about 32% at λ 6620 A to 15% at λ 5078 A. The lowest value of 22% at λ 6620 A was recorded for the umbral intensity of a spot on May 24. Microphotometer records of two spots are reproduced showing the discontinuous nature of the transition from the umbra to the penumbra first observed visually by Secchi. Tables and curves of I. (λ, T*)/I (λ, T) based on Planck’s radiation law are given and the effective temperatures of the spots calculated. Odgers’ theory of the “bright rings” in sunspots is considered and it is pointed out that the observed small values of excess intensity of the bright rings probably imply that sunspots extend to appreciable depths below the photosphere.

Evidence for the existence of the “emission layer” in the atmosphere

SummaryThe theory of radiative equilibrium demands that on the average the total amount of energy absorbed by the earth and its atmosphere in the form of short-wave solar radiation should be exactly equal to the total amount of energy given back to space in the form of long-wave heat radiation. From a study of the absorbing and radiating properties of the atmosphere, F. Albrecht arrived at the fundamental result that the major contribution to the long-wave heat radiation into outer space originates from a layer of some three to four kilometres thickness in the upper troposphere, which he designates as the “Emission Layer”. The emission layer is thus a portion of the upper atmosphere which is continually cooling due to radiative loss of heat. The height of the emission layer is a function of the water vapour content of the atmosphere; it is more when the atmosphere is hot and humid and less when the atmosphere is cold and dry.The author has made a detailed study of the thermal structure of the atmosphere over Agra based on the results of sounding balloon ascents over a period of ten years. A number of interesting features find a ready explanation on the assumption that the emission layer over Agra is located approximately between 11 and 14 gkm. in the monsoon months and between 8 and 11 gkm. during the remaining months, —an assumption in conformity with Albrecht’s work. The observed seasonal variations in the thermal structure of the atmosphere over Agra thus lend, strong evidence for the existence of the emission layer in the atmosphere and the variation of its altitude depending upon the moisture content of the atmosphere.

The Raman spectra of crystal powders

SummaryThe paper deals with the application of the Raman effect to the study of the exchange reaction between NH4Cl and D2O. The Raman spectra of thed-ammonium chlorides ND4Cl, ND3HCl and ND2H2Cl obtained by exchange reactions have been reported. The spectral data are complete in the case of ND4Cl while they are incomplete in the case of the other two compounds. The Raman spectrum of ND4Cl is compared with that of NH4Cl and discussed in some detail. The spectrum of the water recovered from the exchange reaction has been photographed directly and also as water of crystallisation in strontium chloride. The results are compared with the Raman spectra of liquid H2O and D2O in the one case, and with the spectrum of SrCl2·6H2O in the other. There appears to exist differences in the structure of the water band in the Raman spectrum of the water of crystallisation of the salt when H2O is replaced by D2O.

The Raman spectra of some simple molecules

SummaryThe Raman spectra of dimethyl ether, phosgene,n-butane, ethylene diamine, ethylene glycol, ethylene dichloride, ethylene dibromide, acetyleue tetrachloride, acetylene tetrabromide and hexachloroethane have been studied afresh. The Raman frequencies of phosgene have been classified with the aid of polarisation data. Polarisation measurements have also been made in the case ofn-butane, ethylene glycol, ethylene dichloride, ethylene dibromide, and acetylene tetrabromide. A brief discussion of the spectra of the ethane derivatives in relation to the problem of “free rotation” is added.

The Raman spectra of some boron compounds

SummaryThe Raman spectra of methyl and ethyl borates have been carefully investigated, and it is found that the Raman frequencies previously reported for these substances require considerable revision. The Raman spectrum of methyl borate in the region of low frequencies shows great similarity to the spectra of the tri-chlorides of phosphorus and arsenic, and this similarity is strikingly brought out by the polarisation characters of the Raman lines. A pyramidal structure is postulated for the B(OCH3)3 molecule, the group (OCH3) being treated as a single unit. The observed and calculated frequencies are in fair agreement. The Raman spectrum of boron tri-bromide is reported for the first time, and consists of two very intense lines and three very weak ones. These are compared with the frequencies of the tri-chloride. Only one line was found in the case of boric acid, which is attributed to the totally symmetrical vibration of the molecule.

On the convergence error in depolarisation measurements

7. SummaryThe scattering of light in an interference field is discussed, and it is shown that for the simple case of two parallel plane-polarised intersecting beams, the depolarisation at the interference maxima gives the correct value, while at the interference minima the depolarisation ratio is reversed. The average of the depolarisation taken over the whole field is higher than the correct value. The treatment is extended to the cases in which a lens covered with a square aperture, and with a circular aperture, respectively, is used to concentrate the light on the scattering medium. It is shown that the observed values of the depolarisation would deviate from the genuine values by a correction factor which involves the square of the angle of convergence. The observed depolarisationρ is given byn