This communication describes techniques, new to radio astronomy, which permit the analysis of electrical signals at radio-frequencies by optical methods.

Two applications will be described: the first is to a spectrograph which gives the instantaneous power spectrum of a single broad-band electrical signal; the second is to the analysis of the signals from a number of aerials of an array in order to form a simultaneous image of the brightness distribution of the region of the sky under observation.

This work is aimed at understanding the phenomena which affect the sharpness and stability of optical images transmitted through the atmosphere. A brief description is given of the results obtained to date from an experimental field-study directed at establishing a connection between optics and meteorology. Most of the work has, so far, been conducted in daytime because our main application is to solar astronomy; other fields such as surveying, aerial reconnaissance and so on can also benefit from basic research in atmospheric optics.

A horizontal line of sight over uniform, level terrain presents the simplest case for study. The optical transfer function (OTF) of the system comprising an air-path and telescope objective has been measured with an image analyser which is a modified form of stellar seeing-monitor. The outputs of this analyser are proportional to the modulus and argument of the OTF. The modulus, or modulation transfer function (MTF), is a measure of image contrast; the fluctuations of the argument measure image movement, or “dancing”. The OTF is a function of spatial frequency f (cycles per unit distance) which may be altered by radial movement of the scanning graticule of the image-analvser.

The Astronomical Society of Australia was formally constituted at an Inaugural Meeting held at 2 p.m. on Wednesday, 30th November, 1966, in the Grounds of the University of Sydney.