The measurements of the first ionization coefficient alp for air, without and with transverse magnetic fields, are reported in this paper. These were carried out using coaxial cylindrical electrodes to reduce the loss of electrons due to their drift in the E x H direction. The range of measurement covered the values of Elp between 200 and 600 V cm-1 torr-1 and those of H/p between 200 and 1400 G torr-1. The validity of the equivalent pressure concept was tested for the complicated medium like air. It has been shown that a satisfactory agreement between the theoretical and experimental values of alp, Hip and E/p was obtained for low values of Elp (< 300 V cm-1 torr-l) provided the collision frequency was taken to be an increasing function of Elp, instead of a constant as was assumed for hydrogen. At higher values of E/p (> 300), however, the observed values of alp, Hlp and'Elp were below those calculated on the basis of the equivalent pressure concept. A few measurements of ./p were also carried out using the pressure variation technique, and its operational utility has been established from the identical nature of the results.

A low-coherence interferometer for optical information hiding that ensures security of an optical image by hiding the image behind a light-scattering medium is demonstrated. The interferometer has a distinctive feature in that modulation of the optical-path difference between the object and reference arms is performed with a manual operation. The main advantage of the operation method is the absence of expensive optomechanical parts in the interferometer.

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