Chain Reaction, Radio 4<br/>The Essay: Johnson Now, Radio 3

And Robert "Kryten from Red Dwarf" Llewellyn begat Dave Gorman, who begat Frank Skinner, who begat Eddie Izzard ... It's a neat idea, Chain Reaction, now in its fifth series, in which somebody is the interviewee one week and interviewer the next. It's nicknamed (by whom I'm not entirely sure) "the tag-team talk show" – although, as any self-respecting pedant would point out, that would entail a two-man interviewing team taking it in turns to chat to one or other of two interviewees. And they'd all be wearing leotards.

The chain in the first series, back in 1991, broadcast over four successive nights on Radio 5, revealed itself impressively: Ralph Steadman, John Cleese, William Goldman, Ian McKellen, Glenys Kinnock. Since its revival in 2005 it's proceeded in a rather less stellar fashion, though it's jolly enough. As it should be, given its comic-heavy cast list: in the 24 programmes since that first outing, only three interviewees haven't hailed from comedyworld.

Which isn't to denigrate it, particularly: it's not Face to Face or In the Psychiatrist's Chair, but then neither is it Friday Night with Jonathan Ross, praise the Lord. This week was Skinner vs Izzard, old muckers of 20 years' standing chewing the fat. Mutual mastication, some might say, and it was indeed deeply chummy and cosy. But would Skinner have got more from his guest if he'd waded in like Jeremy Paxman? Unlikely. His final words were over the top and out of sight, however. "You are a living example of what courage can achieve," he gushed. "The bravest and most courageous comic I've seen." Next week: Saint Eddie interviews Jesus Christ.

Chain Reaction 1770 might have had James Boswell talking to his boss, Samuel Johnson. Unable for obvious reasons to provide that, the BBC has been marking the good doctor's tercentenary with a raft of programmes on Radio 4, while on Radio 3 from Monday to Friday The Essay, that late-night home of the high-flown, was devoted to him. Tuesday's had the linguistics boffin David Crystal wondering what Dr J would have made of the internet.

As you might imagine, Crystal thinks he would have loved it, "the scale of the thing, the sheer size". Sheer size certainly characterised Johnson's own project, the Dictionary, with its 42,000 entries and 120,000 definitions. He'd have hated Wikipedia, though, Crystal reckons – too many unchecked and unsourced facts swilling round for his meticulous mind. He needed certainties, not assertions. At the start of his project he said he wanted "to fix the English language", but by the end he was more humble, and in the Dictionary's preface he admitted his presumption. "I flattered myself for a while," he wrote. On Chain Reaction 1770 he'd have had his interviewer to do that for him.