In 1894 his Heidelberg School-influenced painting, a bathing scene set on the Cooks River By Tranquil Waters (1894) caused a small scandal, but was purchased by the Art Gallery of New South Wales.

While influenced by the Heidelberg School, Long's first successful painting, By Tranquil Waters (1894), shows a markedly different engagement with the Australian scene: where Heidelberg artists such as Arthur Streeton and Frederick McCubbin showed the Bush as a place of work and struggle (and occasional sentimentality), Long's painting of young naked bathers is hedonistic and charged with low-key eroticism – the eroticism, rather than the nudity per se, was the cause of the scandal.

After 1895 Long moved even further from the Heidelberg School's approach to the Australian landscape (a fusion of Victorian genre painting and a Barbizon-like plein air informal realism), seeking instead to achieve "soulful and graceful evocations of the spirit of the land, as did the Greeks and their beautiful myths."

Long's greatest triumph in this style was The Spirit of the Plains (1897), using the flowing patterns and pastel colours of Art Nouveau to create a poetic vision of the Australian bush as the incongruous setting for a naked Grecian wood-nymph leading a procession of dancing brolgas.

"Synthesising shimmering visual form, mythological subject and musical allusion Long established his vision of landscape as a dream-like, poetic formulation.