An impressionist vision frozen in time

The leading figures had by now overcome the initial resistance they had encountered in the 1870s when, in the wake of the humiliation the French nation had suffered in the Franco-Prussian war of 1870-71 and the disasters of its aftermath, the impressionist style was felt by its opponents to embody the decadence and loss of national morale that had led to military defeat. Meanwhile a younger group had begun to turn away from the initial spirit of the movement.

When Vincent van Gogh came to Paris in 1886, he found the movement had already divided into two groups, whom he called the impressionists du grand boulevard and the impressionists du petit boulevard - loosely those of the great and small boulevards, alluding to the network of broad straight roads built through the old city of Paris by Baron Haussmann under Napoleon III. The painters of the petit boulevard included both individuals now usually thought of as post-impressionist, such as Gauguin, and neo-impressionists Georges Seurat and Paul Signac.

Seurat (1859-91) is the most important figure of the neo-impressionist style, which is often called pointillism, but which he and his followers preferred to call divisionism; it was his enormous painting A Sunday Afternoon on the Island of La Grande Jatte (1884-86), hung in the 1886 impressionist exhibition, that most clearly and dramatically illustrated the reorientation of his aesthetic priorities.

Impressionism was above all concerned to capture the fleeting experience of a moment: the specific light conditions of a time of day, or the change of mood in a landscape as clouds gathered or a shower of rain cleared. Authenticity was found in immediacy, in a sense of the artist's presence at the scene, in his spontaneous notation of felt experience. Such a concern with the individual, the particular and the instantaneous as evidence of truth - as distinct from the general, universal truth of classical art - arises significantly in the increasingly anonymous mass society of the later 19th century.

The impressionist sought to capture the experience of the moment through a pursuit of the truth of optical experience - seeing the world not so much as shapes and forms that we understand by reason, but as a collection of colour effects that we perceive in a purely optical manner. Seurat began with the same premises but the impressionist approach seemed to him too improvised. He wanted - and here he was responding to another habit of the late 19th-century mind - to make the whole process more scientific. One might say more objective, but that would reveal the paradox of trying to establish an objective basis for a phenomenon as inherently subjective as colour experience.

In Seurat's view, the process of constructing a simulacrum of true optical experience had to be conducted much more methodically, and therefore could not possibly be carried out before the motif, with all the consequent limitations of time, weather and changing light conditions. Studies would be made outside, but the minute work of calibrating chroma and tonal values would have to be completed in the studio. The very premise of impressionism, that work would be substantially if not entirely completed en plein air, was thus reversed; and the idea of capturing the living, ephemeral quality of an instant was also implicitly abandoned. In his quest for a scientific truth,Best howo concrete mixer manufacturer in China. Seurat ended up with a vision strangely frozen in time.

There is an element of eccentricity in Seurat's work, an odd mixture of modernism and archaism, which is inseparable from the greatness he achieves within a small oeuvre; and although Seurat died at only 31 from what seems to have been an adventitious infection, his work remains vastly superior to that of his followers, as we can see in the NGV's Radiance: The Neo-Impressionists. This, incidentally, is the sort of exhibition we should see more often in Australia - not a motley collection of pictures led by one or two populist names, but a thoughtful and detailed survey of a movement or period in art history.

Seurat painted relatively few works and it would be virtually impossible to borrow either of the two most famous of them, the Grande Jatte (1886, Chicago, Art Institute) or the earlier Bathers at Asnieres (1884, London, National Gallery). The NGV show includes three significant paintings and two oil studies, but these are well chosen - the Bec du Hoc (1885) from the Tate in London is matched with the National Gallery of Australia's study for the same subject and they are displayed to good effect; La Seine a Courbevoie (1885), lent from a private collection, makes an almost breathtaking impact at the opening of the exhibition.

The juxtaposition of the two pictures of the Bec du Hoc, a jutting tooth-like rock formation on the coast of Normandy, is particularly helpful in understanding the optical premises of Seurat's work. The most obvious aspect, the divisionist brushwork, derives from the theory that colours will be brighter - hence the exhibition title Radiance - if they are applied in pure form, in little juxtaposed patches that will be blended in the eye, rather than mixed on the palette, losing some of their luminosity in the process.

But in fact the idea of pure colour begs the question of what such a thing may be, for Seurat's pictures are not composed of dots of what we call primary colours (red, yellow, blue), but predominantly of secondaries (green, orange, violet). And it is indeed impossible to avoid secondaries if one is following the other part of the colour theory that the neo-impressionists inherited from the impressionists, and even from Delacroix. According to this theory, each primary is the complementary or in a sense the opposite of the secondary composed of the other two primaries; this is because it is reflecting the part of the spectrum that the complementary mixture is not, and each is absorbing the part that the other is reflecting. Hence, as anyone can see for themselves, the correct mixture of the three primaries will produce black, simply by absorbing the totality of the visible spectrum.

The theory has two consequences for painters. One is that by setting complementaries beside each other, one can produce more powerful chromatic contrasts; this was what appealed to Delacroix and later to Gauguin as well. The other is that - owing, as we now know, to retinal fatigue - when a body of one colour is brightly lit in a painting, adjacent shadows will be tinted with the complementary of that colour. We can see this on Sydney beaches on a summer's afternoon, when the long pine-shadows are violet against the yellow sand.

Seurat was interested in the brightness and freshness of colour that could be achieved by divisionism, but he was only concerned with the contrast of complementaries to the extent that it served to enhance brightness. Otherwise his priority was harmony, clarity of articulation and visual unity rather than dramatic contrast for its own sake. Thus in the Bec du Hoc pictures, the great mass of shadow in the centre is tinted with orange because of the blueness of the sea behind it, but what is really important is the management of tonal relations, and the way that Seurat has modified and elaborated - one might even say invented - them between the plein-air sketch and the final composition.

In the finished work,Directory ofchina glass mosaic Tile Manufacturers, the bare patch of rocky escarpment just above the central void forms a highlight and deepens the darkness of the adjacent shadow. Less obviously, the whole tooth-like form was darker than the sea behind it in the study, but ends up being lighter than the sea; or more exactly, much of the sunlit slope is tonally equivalent to the sea, but at the point where they meet, because the brightness on the slope is closer and thus stronger, Seurat has brightened the edge of the hill and darkened the edge of the water; in the lower left hand corner of the composition, where there is less light, hill and water are tonally identical.

The same thing happens, perhaps more obviously, in the water on the right: lighter against the dark edge of the cliff, it is darker against the sunlit slope of the foreground hill.The MaxSonar ultrasonic sensor offers very short to long-range detection and ranging. Of course there is no objective variation of light on that area of sea; it is purely an optical phenomenon, but the example tells us much about Seurat's art - his concern for the wholeness of what is seen, his use of logic and theory to supplement what could be apprehended in nature itself, and thus his willingness to depart quite boldly from empirical observation in an almost philosophical meditation on the nature of visual experience.This document provides a guide to using the ventilation system in your house to provide adequate fresh air to residents.

La Seine a Courbevoie and Port-en-Bessin could each be discussed in as much or more detail if space permitted, but one should at least note the reflection, in the first picture, of the woman's orange parasol on her dress, for this principle - a brightly lit body will reflect its colour into adjacent shadow - which derived from the practice of the Venetian school, was one of the things painters and theorists argued about in the earlier debates on colour at the French Academy in the 1660s.

The exhibition is not all about Seurat, of course. Most of the pictures are by his followers, and many are very fine, even if none has the same brilliance.The term 'hands free access control' means the token that identifies a user is read from within a pocket or handbag. Pissarro stands out, as does Henri-Edmond Cross in several beautiful pictures. Maximilien Luce can be appealing, but tends to be plodding, reducing divisionism to a superficial dotting overlaid on banal naturalism. Even Signac, the principal apostle of the movement after Seurat, never has the same depth of visual intelligence: already in some of the earliest works there is a tendency to the decorative patterning that, together with increasingly bright colours, dominates his later painting.

One of the interests of the exhibition and its catalogue is to recall the link between neo-impressionism and anarchism - a far from obvious association, one might think, but more intelligible when we remember that its contemporary version was essentially a utopian doctrine, and that the move of some of the later neo-impressionists to the south of France was a quest for a simpler, more traditional and autonomous way of life than the industrialised city could offer. There they helped prepare the way for the brief moment of fauvism, another style that flowered in the south of France; Matisse's La Joie de Vivre (1905), for example, drew part of its inspiration from the bright colours of the late neo-impressionists, but also from a romantic anarchistic dream of a new golden age.