Melvyn Bragg and guests discuss the voyage of HMS Challenger which set out from Portsmouth in 1872 with a mission a to explore the ocean depths around the world and search for new life. The scale of the enterprise was breath taking and, for its ambition, it has since been compared to the Apollo missions. The team onboard found thousands of new species, proved there was life on the deepest seabeds and plumbed the Mariana Trench five miles below the surface. Thanks to telegraphy and mailboats, its vast discoveries were shared around the world even while Challenger was at sea, and they are still being studied today, offering insights into the ever-changing oceans that cover so much of the globe and into the health of our planet.The image above is from the journal of Pelham Aldrich R.N. who served on the Challenger Surveying Expedition from 1872-5.WithErika Jones Curator of Navigation and Oceanography at Royal Museums GreenwichSam Robinson Southampton Marine and Maritime Institute Research Fellow at the University of SouthamptonAndGiles Miller Principal Curator of Micropalaeontology at the Natural History Museum LondonProducer: Simon Tillotson

Melvyn Bragg and guests discuss the speeches that became a byword for fierce attacks on political opponents. It was in the 4th century BC, in Athens, that Demosthenes delivered these speeches against the tyrant Philip II of Macedon, father of Alexander the Great, when Philip appeared a growing threat to Athens and its allies and Demosthenes feared his fellow citizens were set on appeasement. In what became known as The Philippics, Demosthenes tried to persuade Athenians to act against Macedon before it was too late; eventually he succeeded in stirring them, even if the Macedonians later prevailed. For these speeches prompting resistance, Demosthenes became famous as one of the Athenian democracy’s greatest freedom fighters. Later, in Rome, Cicero's attacks on Mark Antony were styled on Demosthenes and these too became known as Philippics.The image above is painted on the dome of the library of the National Assembly, Paris and is by Eugene Delacroix (1798-1863). It depicts Demosthenes haranguing the waves of the sea as a way of strengthening his voice for his speeches.With Paul Cartledge A. G. Leventis Senior Research Fellow at Clare College, University of CambridgeKathryn Tempest Reader in Latin Literature and Roman History at the University of RoehamptonAndJon Hesk Reader in Greek and Classical Studies at the University of St AndrewsProducer: Simon Tillotson

Melvyn Bragg and guests discuss the Bauhaus which began in 1919 in Weimar, Germany, as a school for arts and crafts combined, and went on to be famous around the world. Under its first director, Walter Gropius, the Bauhaus moved to Dessau and extended its range to architecture and became associated with a series of white, angular, flat-roofed buildings reproduced from Shanghai to Chicago, aimed for modern living. The school closed after only 14 years while at a third location, Berlin, under pressure from the Nazis, yet its students and teachers continued to spread its ethos in exile, making it even more influential.The image above is of the Bauhaus Building, Dessau, designed by Gropius and built in 1925-6WithRobin Schuldenfrei Tangen Reader in 20th Century Modernism at The Courtauld Institute of ArtAlan Powers History Leader at the London School of ArchitectureAnd Michael White Professor of the History of Art at the University of YorkProducer: Simon Tillotson

Melvyn Bragg and guests discuss the rebellion that broke out in Jamaica on 11th October 1865 when Paul Bogle (1822-65) led a protest march from Stony Gut to the courthouse in nearby Morant Bay. There were many grounds for grievance that day and soon anger turned to bloodshed. Although the British had abolished slavery 30 years before, the plantation owners were still dominant and the conditions for the majority of people on Jamaica were poor. The British governor suppressed this rebellion brutally and soon people in Jamaica lost what right they had to rule themselves. Some in Britain, like Charles Dickens, supported the governor's actions while others, like Charles Darwin, wanted him tried for murder. The image above is from a Jamaican $2 banknote, printed after Paul Bogle became a National Hero in 1969.With Matthew J Smith Professor of History and Director of the Centre for the Study of the Legacies of British Slavery at University College LondonDiana Paton The William Robertson Professor of History at the University of EdinburghAndLawrence Goldman Emeritus Fellow in History at St Peter’s College, University of OxfordProducer: Simon Tillotson

Melvyn Bragg and guests discuss the celebrated British poet of World War One. Wilfred Owen (1893-1918) had published only a handful of poems when he was killed a week before the end of the war, but in later decades he became seen as the essential British war poet. His works such as Anthem for Doomed Youth, Strange Meeting and Dulce et Decorum Est went on to be inseparable from the memory of the war and its futility. However, while Owen is best known for his poetry of the trenches, his letters offer a more nuanced insight into him such as his pride in being an officer in charge of others and in being a soldier who fought alongside his comrades.WithJane Potter Reader in The School of Arts at Oxford Brookes UniversityFran Brearton Professor of Modern Poetry at Queen’s University BelfastAndGuy Cuthbertson Professor of British Literature and Culture at Liverpool Hope UniversityProducer: Simon Tillotson

Melvyn Bragg and guests discuss one of the greatest changes in the history of life on Earth. Around 400 million years ago some of our ancestors, the fish, started to become a little more like humans. At the swampy margins between land and water, some fish were turning their fins into limbs, their swim bladders into lungs and developed necks and eventually they became tetrapods, the group to which we and all animals with backbones and limbs belong. After millions of years of this transition, these tetrapod descendants of fish were now ready to leave the water for a new life of walking on land, and with that came an explosion in the diversity of life on Earth.The image above is a representation of Tiktaalik Roseae, a fish with some features of a tetrapod but not one yet, based on a fossil collected in the Canadian Arctic.WithEmily Rayfield Professor of Palaeobiology at the University of BristolMichael Coates Chair and Professor of Organismal Biology and Anatomy at the University of ChicagoAnd Steve Brusatte Professor of Palaeontology and Evolution at the University of EdinburghProducer: Simon Tillotson

Melvyn Bragg and guests discuss one of the influential painters at the heart of the French Impressionist movement: Berthe Morisot (1841-1895). The men in her circle could freely paint in busy bars and public spaces, while Morisot captured the domestic world and found new, daring ways to paint quickly in the open air. Her work shows women as they were, to her: informal, unguarded, and not transformed or distorted for the eyes of men. The image above is one of her few self-portraits, though several portraits of her survive by other artists, chiefly her sister Edma and her brother-in-law Edouard Manet. With Tamar Garb Professor of History of Art at University College LondonLois Oliver Curator at the Royal Academy and Adjunct Professor of Art History at the American University of Notre Dame London.AndClaire Moran Reader in French at Queen's University BelfastProducer: Simon Tillotson

Melvyn Bragg and guests discuss the military order founded around 1119, twenty years after the Crusaders captured Jerusalem. For almost 200 years the Knights Templar were a notable fighting force and financial power in the Crusader States and Western Europe. Their mission was to protect pilgrims in the Holy Land, and they became extremely wealthy yet, as the crusader grip on Jerusalem slipped, their political fortune declined steeply. They were to be persecuted out of existence, with their last grand master burned at the stake in Paris in 1314, and that sudden end has contributed to the strength of the legends that have grown up around them.WithHelen Nicholson Professor of Medieval History at Cardiff UniversityMike Carr Lecturer in Late Medieval History at the University of EdinburghAnd Jonathan Phillips Professor of Crusading History at Royal Holloway, University of LondonProducer: Simon Tillotson

Melvyn Bragg and guests discuss an atomic particle that's become inseparable from modernity. JJ Thomson discovered the electron 125 years ago, so revealing that atoms, supposedly the smallest things, were made of even smaller things. He pictured them inside an atomic ball like a plum pudding, with others later identifying their place outside the nucleus - and it is their location on the outer limit that has helped scientists learn so much about electrons and with electrons. We can use electrons to reveal the secrets of other particles and, while electricity exists whether we understand electrons or not, the applications of electricity and electrons grow as our knowledge grows. Many questions, though, remain unanswered.With Victoria Martin Professor of Collider Physics at the University of EdinburghHarry Cliff Research Fellow in Particle Physics at the University of CambridgeAndFrank Close Professor Emeritus of Theoretical Physics and Fellow Emeritus at Exeter College at the University of OxfordProducer: Simon Tillotson

Melvyn Bragg and guests discuss Plato's account of the once great island of Atlantis out to the west, beyond the world known to his fellow Athenians, and why it disappeared many thousands of years before his time. There are no sources for this story other than Plato, and he tells it across two of his works, the Timaeus and the Critias, tantalizing his readers with evidence that it is true and clues that it is a fantasy. Atlantis, for Plato, is a way to explore what an ideal republic really is, and whether Athens could be (or ever was) one; to European travellers in the Renaissance, though, his story reflected their own encounters with distant lands, previously unknown to them, spurring generations of explorers to scour the oceans and in the hope of finding a lost world.The image above is from an engraving of the legendary island of Atlantis after a description by Athanasius Kircher (1602-1680).With Edith Hall Professor of Classics at Durham UniversityChristopher Gill Emeritus Professor of Ancient Thought at the University of ExeterAndAngie Hobbs Professor of the Public Understanding of Philosophy at the University of SheffieldProducer: Simon Tillotson