We are still acknowledging our 21st-century debts to the energy, curiosity, determination and passion for discovery of a host of Victorian polymaths, and here is another. Sir Charles Eastlake (1793-1865) was a painter, scholar, author, collector and translator – fluent in German, French, Italian – and the first director of the National Gallery, rising above disputes with trustees and the government to set the scene for the role it plays today.

Down the stairs the visitor enters a sequence of galleries gleaming with gold, seemingly illuminated by softly filtered evening light and flickering candles: here be a treasure house of stories in paint: saints, sinners and the narrative of the divine made flesh, from the Annunciation to the crucifixion.  Some 40 Italian altarpieces, from the 13th through to the 15th centuries – some whole but most just fragments – are theatrically displayed to suggest the atmosphere of late medieval and early Renaissance Italian churches, monasteries and convents.

The National Gallery has done it again: a small but perfectly formed exhibition in their little Room 1, now a by-word for intelligent show-making. Something new, something revelatory, something profoundly beautiful – what more can the gallery-goer ask? The Ashcan School is not widely known outside the USA, and I can think of no better introduction than this dozen-canvas-strong showing of some of the highlights (and, it must be admitted, a couple of low-lights as well).

Jan, or Janin? Gossart, or Gossaert? Or Mabuse? After a mere five centuries, we haven’t settled on a name quite yet (even for this exhibition: at the Metropolitan Museum, the same show spelt it “Gossart”). We don’t know where he was born, although Maubeuge, then in Hainault, now in France, is the best guess, hence “Mabuse”. His birth date too is a mystery: the Grove Dictionary of Art suggests 1478, while the National Gallery just shrugs and gives us “active 1503”. What is in no doubt, however, in this very model of an exhibition, is that Jan Gossaert represented not merely one of the peaks of northern Renaissance art, but that, in a constantly surprising career, he also synthesised great swathes of the Italian art world, both classical and Renaissance, creating something new and hugely potent.

Oh dearie, dearie me. Modern Perspectives sounded like it had such promise. Running alongside the big Canaletto show in the Sainsbury wing of the National Gallery, two finished works and one work in progress by Ben Johnson are on show in Room One. The idea is to look at a contemporary artist who, like Canaletto and his coevals, produces panoramic views of cities. Johnson, despite his quasi-illustrative, photo-realist style, says he produces not "topographical representations of a real place, but perhaps a manifestation of a dream... timeless and transcendent". Wouldn’t it be pretty to think so?

Well, we all make mistakes. Or, in my case, we (I mean “I”) sometimes just fail to look. This new, small but perfectly formed exhibition of Bridget Riley’s work in the National Gallery’s Sunley Rooms follows the pattern that the gallery has developed over the years, with a single artist entering into a conversation with the great art of the past. Riley’s conversation is gripping, and one of the things it says (to me) is, “Shame on you for not looking.”

People love Canaletto, and the title of this exhibition - which puts the setting of the paintings above the artist who did them - gives a good idea why. Venice as a place and an idea is perennially popular, and Canaletto gives us the big views – the Doge’s Palace, the Grand Canal, the Rialto – in painstakingly literal detail.