Two artists on different wavelengths

Nothing is ever quite nothing. Works, however minimal, always have something going on in them. You thought it was near-on nil, total silence, total vacancy.

But slowly, if you can be bothered, you start to notice tiny variations, interruptions. And if there is no competition then the little there is can draw more attention. The senses become sensitised. Fluctuations become dramatic. Finally, it is quite difficult to get the effects to stay small at all. And if you actually wanted the work to be almost nothing... well, look to the art of Agnes Martin.

People have called her a mystical or transcendental painter. That may sound a bit too big. She was born in Canada in 1912 and she moved to the United States as an adult. Her earlier painting included landscape and surrealist subjects. These works are rarely seen. But about halfway through her long life – in her mid-forties – her art changed gear and was picked up by the New York scene. These are the works now known.

She said: "My paintings have neither objects, nor space, nor time, not anything – no forms. They are light, lightness, about merging, about formlessness, breaking down form." Of course, they do look like something. She emerged first of all with pure grids of lines. Around 1970, she broke off for seven years. Latterly, until her death in 2004, she made ladders of bands, of varying widths, full of pale and thin washes of colour. A group of 11 of these paintings is now showing at Kettle's Yard in Cambridge.

Clearly this is a restricted repertoire, very minimal – though Martin insisted she was not a minimalist, given that term's implication of cool anti-emotionalism. She called herself an abstract expressionist, but that seems much too lush, assertive and romantic. There is a dialogue. It is an art of fine-tuning and tuning-in, on the part of the artist and the viewer.

The show has only one pure linear grid picture. Morning. It is 6ft by 6ft square, as these grid pictures generally are, and it is on the point of being overwhelming. Horizontal lines and vertical lines in graphite: the lines narrow and stretch and open out, creating light and air. You may presume that it is a kind of graph paper. But gradually you become aware that you have been subtly wrong-eyed.

Martin always uses straight lines, but they are never ruled straight lines. They are hand-drawn, wavering straight lines. In other words, whether or not you are conscious of it there is an internal tension in the field of lines, between the expectation of exact geometry and the human errors of its drawing at every point. It is what draws you into it.

The tension is continued into the later paintings. Their bands of hue are far from being strict stripes. Their widths vary slightly. Their colour is never quite put down in uniform areas of hues, but filled with uneven pulsations. Martin's work, she said, very well, "is about perfection as we are aware of it in our minds but that the paintings are very far from being perfect – completely removed in fact – even as we ourselves are."

When it comes to individual paintings, descriptions are quite hopeless. Reproductions are hopeless too. You can name the titles, when they have them: Happy Holiday, Faraway Love, I Love the Whole World. But they are always more simply heartful – or ironic? – than the pictures themselves.

The visual relationships between one faintly coloured band and another, the grouping of bands within a picture, the feeling of weight or rising, opening or pressing, the sense of the painted surfaces becoming ungraspable – these effects can be judged by the eye, to the extent that they can be pointed out, with appropriate gestures and expressions. But discussion seems strange when solitude is the proper response. And in that case, how much needs to be noticed? Isn't the losing of our looking in these canvases the real thing?

You can talk about what Martin's art is about. Sometimes it seems to be a very oblique and abstract image of reality. Its horizontal bands may remotely recall horizons. You can find in some paintings that the colours are obscured by a kind of milkiness, retreating into mist, into distances. So there is a hint of landscape. But equally a painting could be a mood inducer or a stimulator of a state of mind. You are being invited into a feeling of drift, into sheer endlessness, with no association of any sights.

Either way, the crucial thing is to avoid the big void. The temptation is to say, as so often with a minimal art, that at first it seems so little but when you get into it there is so much, so much richness, such abundance. On the contrary. Martin's knack is to keep on the edge of very little. The pale against pale, the barely visible shudder: these tiny departures from the regular and the expected really do stay small. They don't deliver excitement. They require and reward attention, contemplation, meditation, silence, peace. As for the mystical, I don't know. Martin liked that kind of language. But if that's your thing you don't need art, do you? You can get it anywhere.

Now go to the other end of Cambridge and altogether to the other end of art. At the Fitzwilliam Museum you see a series of recent paintings by Maggi Hambling called The Wave. But how could you make a comparison? Martin's painting is muted. Hambling's is garrulous. Martin is in the best possible taste. Hambling is wildly vulgar. Martin is sober. Hambling is preposterous. It is beyond any contrast. In no useful way could these two painters be matched. It seems hardly credible that they could share the name of painting. Just for that reason, it's worth trying to get the mind round it.

Hambling is, I guess, a veteran of British painting. She was born in 1945 and is now strongly associated with the Suffolk coast, where some years ago she erected a monument to Benjamin Britten, a sculpture of such awfulness it should be passed over with a decent tact. On this coast she has been studying the waves of the North Sea. She writes: "As the waves of the sea, these new paintings respond to the energy of their action as they break."

That is a clue. And you want to take it further, take it like this. Imagine a verbal description of some violent waves. They break, they roll, they mount and they crash. They froth and foam and sweep and swirl and swell and spit and splosh and surge and plunge. Then imagine a painterly vocabulary that is exactly the equivalent of this roster of verbal clichés. You have imagined Hambling's paintings.

The energy of water is translated into the energy of paint with a twist of wrist and with spatters and slabs and squiggles and flourishes and flicks. These gestures are forceless because they are so broad and imprecise. Messy, vague, totally superficial in their observation of waves, they have no sense that the movements of water are not just a splurge. They have a structure. In short, it's lively.

Nobody, I suppose, would be likely to admire both these artists. And if we bring these names together, it is only to suggest the galactic distances that stretch within the art universe. Or they do when looked at from one angle, anyway. But Martin and Hambling do, in some sense, co-exist. Both practise, in some sense, landscape. And oddly enough both owe something to abstract expressionism. Fashion cannot accommodate this pair. But sociology could – easily. It is good to remember this. It is a very small world we have.

Agnes Martin: Kettle's Yard, Cambridge (01223 748100) to 11 July, closed Mondays; free; Maggi Hambling: Fitzwilliam Museum, Cambridge (01223 332900) to 8 August, closed Mondays, free