The young, rather homely yet grand gentleman is lounging under a tree, behind him a formal knot garden. His costume is extravagant and rich, and his hat is charming. This exquisite 1590s miniature by Isaac Oliver, watercolour on vellum, titled indeed A Young Man Seated Under a Tree, is the first depiction in art of a knot garden; flowers and plants by the tree are meticulously detailed, and in the background is the classic Renaissance knot garden. 

We think we know it when we see it. But how, pray, do we define beauty? The ancient Greeks thought they had the measure of it. In the 4^th century BC, the “chief forms of beauty,” according to Aristotle, were “order, symmetry and clear delineation.” A century earlier, during the golden age of Athens, Polykleitos, one of the ancient world’s greatest sculptors, set out the precise ratios for the ideal male form in a treatise he called The Canon.

One masterpiece and two superb portraits both dominate and sum up in vivid fashion the complex personality, long life and astonishing trajectory of the first Duke of Wellington

The grand but domestic setting of Hertford House, home of the Wallace Collection, makes a fitting backdrop to an exhibition of paintings by Joshua Reynolds. The Marquesses of Hertford acquired some 25 paintings by Reynolds in the artist's lifetime, and after it, and the 12 that remain in the collection form the focus of this exhibition.

Alexander McQueen designed some dresses to die for. Dominating a wood-panelled room dedicated to Romantic Nationalism, in acknowledgement of his Scottish origins, is a crimson cape worn over a simple white dress. The high collar, puffed sleeves and long train lend the shimmering red taffeta a baronial splendour perfect for dramatic entrances.

Made an Honorary Royal Academician just a few months before he died, in 1993, it’s taken till now for a posthumous Royal Academy survey to finally bring one of the absolute greats of American postwar painting to a UK audience. Of course, for those with long memories, there was the Whitechapel Gallery exhibition of 1991, but though it provided the impetus for the belated honour, it seemed to do little to bring the paintings of Richard Diebenkorn into the public realm.

The unveiling of the Fourth Plinth has, since his election to office, been an opportunity for Mayor Boris Johnson to work the press pen with a comic turn. So, the commission, sponsored by the mayoral office, gets a media-chummy spokesperson whose art critiques add a note of gaiety to proceedings, even if they’re self-evidently at odds with what the artist had in mind. See them as an ongoing election campaign. 

Here is an exhibition that tells us how something we now take totally for granted actually came about: how our love affair with the Impressionists was masterminded by an art dealer, Paul Durand-Ruel (1831-1922). He was a prime mover in inventing the way art is dealt with by commercial galleries and even museums, and is credited as the inventor of the modern art market.

The sight of two old women fighting in the street would probably meet with roughly the same response from passers-by whether it happened today or 200 years ago – a queasy mixture of dismay, embarrassment and amusement. To get close to Goya’s drawing of two ancient crones locked in a wrestlers’ embrace, their toothless faces both grimly determined, is to experience those uneasy sensations just as he surely did.

Recent attitudes to Victorian Britain have changed radically. The popular view used to be of a period filled with a kind of smug imperial confidence, underwritten by the increasing wealth of the industrial age. This ingrained assumption was perhaps epitomised by Lytton Strachey’s 1918 Eminent Victorians, which saw the eminences as bungling hypocrites. And although secret lives might have been as wild as may be, one characteristic myth was that even piano legs had to be obscured with frilly covers for decency.