RADIO / An act of surrender: Robert Hanks on the BBC 2/ Radio 4 collaboration, Arena's Radio Night, and how History Now and Then was made

It's impossible to spend much time thinking about radio without finding yourself brooding on its relationship with television, which has stolen so much of its popular audience, so much of the available money, so much - you may think in gloomier moments, such as listening to Radio 4 sitcoms - of the available talent. There's no doubt that television is now the dominant medium, measured in terms of audience size and influence.

On the other hand, radio is still more important to many, if not most, of us in our daily lives. Arguably. We may, taken en masse, give up more hours to television than we do to radio, and we may even give it more whole-hearted attention during those hours. But television can't infiltrate your life in the same way that radio can; it can only replace chunks of it. Where radio can be a companion, an old chum to make bearable those necessary but intellectually numbing pursuits (cleaning the bath, brushing your teeth, earning a living), television is an awkward child, sat in the corner screaming for attention. Although, to be scrupulously fair, television does have the inestimable advantage that you can turn the sound down and watch the Ceefax subtitles in silence when old chums telephone.

All of which is a prelude to discussing Arena's Radio Night, broadcast this Saturday simultaneously on BBC 2 and Radio 4. Ostensibly, this was an experiment in bi-media broadcasting, using the resources of both radio and television; in fact - and we should have realised this would happen - what we really got was a single medium, television, with an extra speaker attached.

The only essential difference between radio and television is that there are no pictures; once the two are synchronised, so that the pictures complement the sounds, the difference has vanished. So in one sense, Radio Night represented a kind of act of surrender to the mighty box. You could hear that, too, if you turned off the telly altogether. Radio, geared to Arena's needs, became a rather gappy, hesitant version of itself: where television could fill in the space with pictures, radio was often stumped. The only point was to facilitate the bickering dialogue between Josie Lawrence (playing the voice of radio) and Peter Cook (as the television); and that turned out to be a low-humour zone.

Still, it provided some intriguing illustrations of the distinctive accomplishments of the two media, particularly in a short play by Peter Kavanagh, The Spot FX Man. Peter Vaughan played the man who does sound-effects for radio drama live in the studio, with hinges custom-made for creaking, a selection of bells for tolling, trays of gravel for walking - that's as opposed to recorded sound effects, which you can simply grab off a CD. On television, this was a leisured, austere production, in which the camera ranged happily over shelves of noisy implements; on the radio, the spaces where the pictures fitted were filled by a nostalgic interior monologue about how the FX man came to be this way. But fill the spaces was about all it did; the laziness of the television version was replaced by forced speech ('Yeah, after Eileen I lost interest in all that romance stuff'), and you had the sense that Kavanagh was scrambling frantically to stop the silence getting a hold. Perhaps that's the central problem radio suffers from: a fear of silence.

On the other hand, there are some things that radio does which television could never do half as well: into this category comes the good old talk-shop, as exemplified by History Now and Then (Radio 3, Monday to Thursday).

This was a series of short discussions, chaired by Roy Porter, in which historians talked about different ways of approaching history - history from below versus Great Men's history, men's history versus women's history - and then applied some of the methods in discussions of two old chestnuts, the Industrial Revolution and the Causes of the English Civil War.

Talk doesn't automatically work well on radio - witness Robert Wistrich's The Rebirth of Europe, broadcast in the same slot the previous week, which would have lost nothing by appearing in cold print: that's surely the acid test of what is worth broadcasting. Still, it's impossible to imagine any other medium handling this level of discussion with the degree of spontaneity and zest that Porter got out of his contributors.

At times the atmosphere was almost too bright and breezy; during Tuesday's discussion of gender, Porter turned to one contributor and announced with audible exclamation marks, 'Vic, there's an a-genda (]]) for gender history.' But, mostly, he was an excellent chairman, clarifying ideas, hustling along the arguments and, without visual distractions, generally putting you in the picture.