Portrait of a true genius

On show in the gallery's Sainsbury Wing are nine paintings by Leonardo da Vinci, more than half his known surviving works, and only two of them previously seen in the UK. The Renaissance Titan – scientist, philosopher, engineer, inventor, sculptor and musician as well as artist – produced relatively few paintings, but their impact on Western art has been incalculable.

The exhibition centres on the years (c1482-1499) that da Vinci spent at the court of Ludovico Sforza, Duke of Milan. And the paintings, drawn from as far afield as Poland, France, Russia and the Vatican, are buttressed by a wondrous selection of 50 of Leonardo's sketches, many from the Royal Collection.

The penumbra of the Sainsbury Wing, the pressure of viewers (however mannerly), the modest scale of most of the paintings and the small scale of the drawings, combine to make demands on the concentration. The experience is nonetheless overwhelming.

No need to lament the absence of the Mona Lisa. Two portraits of young women are here to entrance viewers with their enigmatic beauty. First, from Cracow, there's The Lady With An Ermine. She was Cecilia Gallerani, Ludovico's teenage mistress, a vision of refinement with just a hint of a smile in her half-averted face. She clutches the sleekly muscular ermine (a symbol of purity or maybe – dare one suggest – of male lust?) in a somewhat enlarged hand.

Gazing out at the viewer from the neighbouring wall is another young woman, The Belle Ferronniere, who may be the Duke's wife (or another mistress). Her face is fuller, her gaze at once composed and self-contained, and more worldly wise. The psychological subtleties of these two portraits fascinate. They share one physical feature: both women have severely dressed hair. Indeed in the case of Cecilia's, it's not clear where hair ends and head-covering begins.

Perhaps it was the convention of the time for aristocratic women to keep their hair modestly restrained while young men sported tumbling locks. The slightly earlier portrait of The Musician suggests so. The handsome fellow has a mane of curly titian hair topped by his red cap. Pulsing with life and vigour, this three-quarter profile engages the viewer in a ground-breaking way.

The three secular portraits, full of youthful grace, contrast with Leonardo's six other paintings on show, all of which have religious themes. There has been speculation about Leonardo's own religious beliefs, but so much of the patronage of his day was from religious sources and he patently sought the transcendental in his religious art. The twin centrepieces of the exhibition are testimony to this. They are the painter's two versions of The Virgin Of The Rocks, one belonging to the Louvre, the other to the National Gallery.

They have been placed at opposite ends of the main gallery – a dramatic conjunction but not one that lends itself to the instant comparisons that would have been possible had they been side by side. Thus the viewer shuttles from one to the other, trying to keep a particular detail in mind while avoiding entanglement with others on the same pursuit.

Regardless of one's religious persuasion, or lack thereof, these two masterpieces take the breath away with the beauty of their central figures, the mysterious ambience of their setting and, simply, the spiritual power they radiate.

People will be partisan about which they prefer. The earlier French painting has an aura of warmth and humanity (some of its glow, critics say, may be due to the fact that it has not been restored). The same four figures in the later painting – the Virgin, infant Christ, infant John the Baptist, and angel - are perhaps even more exquisite but have acquired a sort of archetypal remoteness. The colours are colder, steelier.

These two great juxtaposed paintings will haunt all who see them. The recently attributed Christ as Salvator Mundi, an image of a ringleted Christ holding an orb and looking a little like the actor Charles Dance, does not communicate such spiritual force. The Vatican's unfinished St Jerome shows Leonardo's fascination with anatomy.

The Virgin and Child in the Duke of Buccleuch's stolen and recovered Madonna Of The Yardwinder are lit by the incomparable softness and radiance that Leonardo brought to human flesh, though the background is probably by another's hand. St Petersburg's Madonna Litta with suckling Christ child completes the tally of nine paintings.

There is much else to relish, from the National Gallery's great Burlington House Cartoon of the Virgin and St Anne to a vivid near-contemporary copy of the Last Supper. And of course there are the sketches, from human heads, beautiful or grotesque, to anatomical detail, and even the study of a dog's paws from the National Galleries of Scotland. Paintings by Leonardo's pupils and followers demonstrate the gulf between talent and genius.

Leonardo Da Vinci: Painter At The Court Of Milan, is at the National Gallery, London, until February 5. Advance tickets are sold out; a daily allocation of 500 tickets is on sale from 10am.