Many years ago, when TV was in black and white, and I was very young, they did an interesting demonstration of the way people say what they ought to think, not what they really think. They asked a woman who her favourite artist was, and she said Picasso, she loved all that modern stuff. Then they hypnotised her and ask her the same question, and she said her favourite painter was Constable, traditional landscapes, not that modern stuff she found such hard going ...

At the time I scoffed. I was really into Picasso, and Braque and all those guys, and had no time for trad artists like Constable. I felt sorry for the limited horizons of the woman, even if she was obviously a complete philistine and deserved to be exposed.

And now? Well, now, I think things must have come full circle, because when I look deep into my soul I see that it is years since I thought much about Picasso and that the exhibitions I have most enjoyed in the last couple of years have both been, not of Constable, but certainly of landscape painting from the 19th century.

One, in 2003, was America Sublime, at the Tate. This was a stunning display of huge landscapes of the newly discovered American landmass, by artists quite unknown to the British, like Bierstadt and Cropsey, Cole and Gifford. The other, in 2004, at the National, was Russian Landscape in the Age of Tolstoy. This was a stunning display of huge landscapes of the Russian landmass, by artists quite unknown to us, like Shishkin and Levitan and Kuindzhi (this last man is quite wonderful).

And yet, for all the similarities, there were huge differences. For one thing, it was all new to the Americans. It was as if they were discovering the Garden of Eden, an unknown paradise. For the Russians, the land was just as vast, but well-known. It was Mother Russia, already populated, however sparsely. There were peasants in the fields, churches in the distance, steam boats on the misty rivers.

One painting caught my imagination. It showed a horse-drawn coach setting off down a track. Ahead is a vast wood, and the eye stretches beyond the wood to what looks like the whole of Russia in the distance, through which the coach must go before it reaches anywhere, but the driver knows exactly where he is going. It's all home territory.

In the American paintings, it's the excitement of the new that comes at you. The styles are far more melodramatic; there's lighting, storms, rainbows, sunsets,railway viaducts looking like Roman aqueducts. And suddenly it hits you. This is Hollywood on canvas! These guys are in showbiz! It is no suprise to learn that some of them took their huge canvases back to New York and displayed them like movies, behind curtains which were drawn when the audience paid and entered. Even looking at the tiny reproductions of the Niagara paintings in the catalogue, you can sense the excitement that must have seized the viewers 150 years ago.

In the Russian paintings there was no excitement, a quiet celebration at most. The more common mood was of resignation. There is a painting by Isaak Levitan called The Vladimirka Road, which shows just a dirt track ambling off into the woods, but which would have been well-known to viewers as the road down which political prisoners trudged on the start of their weary way to Siberia. In Russia there was already a history of repression of dissidence. In America that was all still to come.

Well, there you have it. I have been raving about two landscape shows which are long over. I suppose I should now be raving about the Monet, Whistler and Turner show just hitting town. Oddly enough, I have already seen it. I saw it by accident in Toronto last year, on a family visit. I even dragged my 17-year-old son to see it. He was bored stiff. All that old hat landscape stuff, Dad! It's so old-fashioned! Get modern!

One day I'll put you under hypnosis and ask you a few questions, I told him, but I don't think he caught my drift.