This has everything a painting of a superb horse should have - nobility, sleek beauty, enormous, visible strength, and more than a hint of an untameable spirit. It is virtually life-size. It would surely have thrilled the later French Romantic painter Gericault whose own paintings of horses had a similar air of vigorous glory and celebration. But George Stubbs, in his clarity of statement and steady observation, was nevertheless very much a man of the 18th rather than the 19th century.
When he came south to London about 1759, Stubbs' ability and originality as a painter of horses proved to have great appeal for a number of young aristocratic patrons. A love of country living - on a grand scale - was characteristic of such men, and the horse - its breeding and racing as well as its uses for hunting, farming, and mobility - was a prominent feature of these men's style and elegance. Fine horses represented status: they were obvious indicators of birth, power, and wealth.
A natural outcome of this was ''The Horse Portrait,'' and Stubbs, at this period in 18th century England, had few rivals in the art. He had built up (by laborious dissection and drawing) a formidable knowledge of the anatomy of the horse, and he had two other qualities perfectly suited to his clients' wishes: he could use paint to reproduce, with highly convincing realism, the surface of magnificently groomed horses, what one might call their meticulous ''sheen;'' he had also an inborn (or highly developed) feel for lucid composition. With this classical sense of placement and proportion he managed to idealize his subject without contradicting accuracy. However complicated the arrangements in his paintings - for example his frieze-like gatherings of mares and foals - Stubbs always avoided the slightest confusion. This is true also of his paintings of wild animals and of a variety of subjects connected with country life. But when a horse was the main subject, the figures and landscapes, painted with a straightforward simplicity, are never allowed to interfere. The animal may stand as a silhouette against the vast loneliness of a Newmarket sky, with the horizon low and flat, or with nothing but a single tree and an expansive vista of country estate as its setting.
In ''Whistlejacket,'' however, there is no background. This heightens the effect of idealization. It is almost as though the animal is being presented as a ''specimen,'' typical of ''The Horse'' at its grandest, rather than solely as a record of a particular horse.
Two stories have attached themselves to ''Whistlejacket.'' The first may explain the absense of background. This story has it that Charles, 2nd Marquis of Rockingham, who owned the horse and commissioned the picture, originally intended a figure of George III and a landscape to be added by other artists but changed his mind when he saw the masterpiece Stubbs had painted. Basil Taylor, however, notes an alternative in his book on Stubbs: ''An American visitor to (Wentworth) in 1835...was told that Rockingham's decision was due to 'his being offended at the king.' Certainly, during the period of Stubbs' employment, Rockingham, as a Whig, had cause to be aggrieved by the new king's political policy, which was designed to break up his party's monopoly of power.''
The second story is that the lively horse itself tried to interfere with Stubbs while he was painting and that he had to restrain it unassisted, with only his mahlstick to defend himself. The admiration with which he painted the animal's flowing mane and tail, the enormously powerful creature's energy and vigor barely restrained in the alertness of the ears, the turn of the head, and the marvellous glint in the eye - the painting of all these certainly support the notion that the artist had a more than passing acquaintance with Whistlejacket's temperament. Here is horse with a free spirit fit for a king - - even if the king in question may not, in this event, have been considered fit for the horse.