''He is very accurate,'' the painter James Barry wrote to a correspondent about 1765. He was referring to a Liverpool-born artist then working in London: ''There is one Stubbs here,'' he said, ''who paints horses and other animals with a surprising reality.''
It is difficult, in 1982, to entirely appreciate the ''surprising'' nature of Stubbs' accuracy, so accustomed are we to both colour photography and the ''reality'' of its representation of animals. But more than any of his contemporaries, Stubbs was concerned to present the animal kingdom without distortion. At the same time, he was, as an artist, a strong idealist, and it does not seem likely that if, in the late eighteenth century, he had been able to take up photography, he would simply have thrown out his brushes and paints.
The question is whether or not Stubbs' main purpose and achievement was the dispassionate recording of the appearance of animals.
Some of his patrons and associates seemed to think so. John Hunter, the greatest comparative anatomist of his day, and his brother William both commissioned pictures from him of unusual animals, such as an Indian rodent called a ''cavy,'' a ''rhinoceros'' and a ''nyl-ghai.'' They also collected the work of many other artists, and so were hardly indifferent to the aesthetic merit of Stubbs' paintings; but what John Hunter was praising above all was his objective accuracy. ''Good painting(s) of animals,'' he said, ''give much clearer ideas than descriptions. Whoever looks at the picture (of the nyl-ghai), . . . by Mr. Stubbs, that excellent painter of animals, can never be at a loss to know the nyl-ghai, wherever he may happen to meet with it.''
Stubbs was working in a ''rational'' age, at a time when the arts and sciences were far from being separated. He was still quite consistently able to operate between the two worlds, no less than Leonardo and other Italian Renaissance artists had done.
He could study the anatomical structure of human beings and animals with a determined curiosity and, simply, a thirst for knowledge which in no way conflicted with his artistic purposes. He was, in fact, an artist of wide-ranging talents and interests, painting portraits, producing classically ordered scenes of country life and labour, celebrating the ferocity of wild animals in expressive, half-fanciful dramas and making out of popular equestrian portraiture something more sensitive and telling than the mere flattery of successful horse-breeders, wealthy or noble.
It does seem, though, that his interest in anatomy was overriding. He approached it as an artist rather than a scientist. If his pictures of animals brim with vitality, so also do his drawings of skeletons - it seems that the vigour of his art drew breath from his keen interest in structure and organization, in how they are put together and how they work.
Basil Taylor has summed this up neatly by writing that Stubbs designed his pictures with the same disposal of ''weight and force . . . balance and counter-balance,'' that he also found in animals, ''whose posture, motion, coherence and stability depend upon a constantly changing and dynamic resolution of opposed forces.'' But, as this delightful painting ''A Monkey'' shows, all this does not result in the kind of cool detachment one might expect. Stubbs' approach to animals has something more to it than the purely factual and the very competently composed.
Possibly he would have found a camera to be a helpful tool. But there is a slow consideration involved in his transmuting of animals into art which a mechanical device would have been wholly inadequate to encompass. And there is another crucial difference between his approach to animals as an artist, and the recording capacity of photography. It is particularly apparent in ''A Monkey.''
This is Stubbs' active interest in the animals' awareness of him. On more then one occasion verbal descriptions of an animal's reaction to his presence have come down to us. This shows something characteristic about the artist's admiration for animals. They are never mere objects for his brush to depict. Their independence and difference from humans is never forgotten, even when there is evidence that he was aware of similarities. Portraying a monkey, he could scarcely have been unconscious of the slightly unnerving likenesses of these animals to human beings (an observation that did not start with Darwin - even the medieval bestiaries mention it) - and he certainly gives the little creature a setting and centrality not very different from the conventions of human portraiture. But this recognition of its being and individuality does not mean he projected human characteristics onto it.
Instead it is a remarkably unironical and unsentimental portrayal of a sympathetic confrontation of animal and human. Each appraises the other. The monkey has next to no interest in the rich fruit it is supposed to be eating. Its interest, shown in the round eyes staring straight outward, is solely in . . . George Stubbs. That, surely, is the secret of its ''surprising reality.''