The BBC is making sure that our brains get plenty of exercise on Wednesday evenings for the next few weeks as Radio 4 launches two “big” series. In Giants’ Shoulders, Melvyn Bragg takes on the history of science (with a second bout to come next year). In Mysterious Ways, Libby Purves surveys the history and influence of Christianity in Britain.

Bragg begins with Archimedes. He adopts the stance of the non-scientist determined to grapple with an unfamiliar area of knowledge and to spread to other non-scientists the excitement of the discipline. He does this through a rapid series of explorations, programme by programme, of some of the great scientific reputations - Galileo, Newton, Faraday, Darwin... the giants on whose shoulders modern scientists stand.

Bragg interviews modern scientists and historians of science, some of whom may one day have giant status themselves. In “Archimedes”, Sir Lewis Wolpert enthuses us early on with the Greek’s breathtaking achievements - in the manner that one would expect from the chairman of the Committee for the Public Understanding of Science (COPUS).

Archimedes had no earlier shoulders to stand on: “He is the first physicist, the first applied mathematician, and he did it all on his own, from nowhere, ” says Sir Lewis with infectious wonderment.

He regards Archimedes as having “originality and vigour”, the two basic requirements for the debatable accolade of “genius”. The programme continues with contributions from Sir Geoffrey Lloyd, professor of ancient philosophy and science at Cambridge University and the debate turns to the question of whether even Archimedes was a one-off genius or whether there is always a debt to predecessors.

Braggs’s great strength is his impatient determination to understand. He’s not afraid to allow us to hear his mental gears scraping as he tries to come to terms with concepts. The series in the end will depend on the quality of his contributors. Certainly in both of the first two programmes (the second is on Galileo) Bragg has corralled academics who manage to hit exactly the right level for non-scientists.

Libby Purves’s series is different. In her programmes on Christianity she weaves an elegant and thought-provoking documentary tapestry. In the first she looks at buildings, taking us into churches and cathedrals all over the country. She loves the “echoing, elegiac emptiness” of parish churches like Bampton in Oxfordshire and she’s full of interesting asides: the cruciform shape of churches had little to do with the cross, but everything to do with important people wanting to add on side-chapels and extra burial areas.

Libby Purves is keen on cathedrals, mostly pewless, and usually full of activity, but is not so sure about those parish churches, particulary some “Gothic tunnels”, which are fine for interaction with God but hopeless for personal contact among the congregation. She visits a Norfolk church with a pew controversy and reminds us that medieval churches were big, open spaces and that it was the Victorians who cluttered things up with pews.

This programme manages the difficult trick of combining an historical survey with on-the-spot reporting and interviewing and then leads neatly into an intensely heated issue: what to do with the little-used churches which have left such a powerful visual impact on our landscape.

I’d bet Ms Purves’s sympathies are with the “God isn’t as concerned with old buildings as we are” lobby. As somebody elegantly put it “which is more important, the baby or the historic font she’s being baptised in?” After “Buildings” come “Ceremonies”, “Church and State”, “The Clergy”, “Education and the Status of Women” and “Belief”. It promises very well indeed and both series have much to recommend them for A-level students.