Great Works: An Experiment on a Bird in the Air Pump, 1768 (183 x 244 cm), Joseph Wright of Derby

National Gallery, London

Do we feel a certain coolness when we think about the 18th century? Well, we do often find ourselves praising it (or trying to define its nature) for what the head – and not the heart – achieved. Remember these time-honoured terms, for example: the Age of Reason, the Enlightenment, Deism (in which the universe moves along, smooth as clockwork, without any need for the intervention of a personal god). Science was the newest diety. Did not Alexander Pope once write: "God said, 'Let Newton be! And all was light'"?

This great painting seems to be alive with the tensions and the excitements of its historical moment. Its subject is the spectacle of science and how it woos the public – on this occasion that public is a prosperous family seen inside a well-to-do architectural environment, complete with panelled door, pedimented doorway, generous sash windows, a handsome console, and a beautifully made, highly polished table straight out of a contemporary pattern book, on the top of which a drama is being played out.

What exactly is this drama? A scientific experiment is being staged. A bird is suffering inside a glass chamber. In fact, it has fallen into a dead faint. It may even be on the point of death. The standing man who stares directly back at us – the only one who does so in this painting – is in charge of this bird's destiny. He is demonstrating the marvels of not-so-contemporary science in front of a captive audience.

He looks a little wild and charismatic, this man. There is just a touch – in appearance at least – of the John Wesley about him. He is gorgeously tricked out in what to us resembles a velvet bath robe, which is itself held in place by a swashbuckling black sash. He could be an exotic merchant adventurer, this man who stands beside his vacuum pump. This device (by no means newly invented in Wright's time) sucked air from a chamber, and demonstrated how a vacuum was created. The experiment had been conducted time and again – on larks, mice. This time it is the turn of a poor white cockatoo. The bird has plummeted to the bottom of the chamber. We see the scene at a moment of high drama. The lecturer is about to let the air back in. His hand is poised to do so. But will it be too late?

Wright was a great master of dramatisation through the use of light. In this case, the play of light reminds us somewhat of a mingling of Von Honthorst, Caravaggio and Le Brun. Candlelight – where exactly is that candle though? – suffuses the scene, flooding and glossing each of the faces, some in profile, others full-face. Each face, each expression, is wonderfully particularised thanks to the use of this light source. Had this been daylight, the overall effect would have been much duller, much more generalised. We would not have found ourselves giving this degree of minute attention to each of these faces; we would not have noticed how each response is distinctively different.

Yes, just look at the fascinating range of responses, and see how they differ so dramatically from the youngest to the eldest. The youngest are fearful in the extreme – one of them cannot even bear to look at this poor, suffering bird – and the oldest (that seated man on the right of the table who leans on his cane) is the most steadily ruminative. And then, quite different again, there is the young couple who are standing to the left of the man who is the master of ceremonies. They are engaging in a bit of idle banter, aren't they? They are here because they are interested, but most of all they are pleased with each other, we feel.

Like a brilliant visual trick, the scene itself appears to have emerged from that darkness and, at the painting's outer edges, to be sinking back into it. The presentation enhances our feeling that what is happening here is a form of prestidigation. Another lovely detail appears at the extreme right of the painting, near that boy who has his hand on the cord that might release the cage – should that poor bird ever need a cage again, and not a fresh, scooped corner of the kitchen garden. Through the window we see a moon swimming through clouds. That detail adds a tiny pulse-beat to the atmosphere here.

ABOUT THE ARTIST

Joseph Wright of Derby (1734-97) was best known for his paintings of industrial scenes, and for his dramatic use of lighting – furnace light, candlelight. He painted hard-bitten toil in the workshops and the forges of the Industrial Revolution. At one time in his career, he had ambitions to be a successful portrait painter, but Gainsborough beat him at that ruthless game.