And wild that world could be as yogis strove to be godlike and gods advertised themselves as transcendent yogic adepts. In a devotional painting from Rajasthan, dated around 1800, a smoky-blue Vishnu has Master of the Universe written all over him: The sun appears in one eye, the moon in the other; heaven spreads across his chest, hell spills down his legs. And in a slightly earlier painting, depicting a scene from the Bhagavad Gita, Krishna reveals himself as the Lord of Yoga, turning himself into a kind of giant, purple-and-gold machine of fate, his dozens of spinning arms slicing the air like blades. It’s an awesome sight, but scary. You can’t tell whether his energy is benign or threatening, whether you should move in close or stay out of his way. Over the centuries, human yogis provoked similarly ambivalent reactions.

Medieval Indian texts suggest that many people found mendicant yogis alien and off-putting, even menacing. To the Mughal emperors who ruled India from the early 16th to early 18th centuries, they were objects of fascination. Although formally Muslim, some of the rulers were wide-ranging spiritual seekers who surrounded themselves with holy men: Sufi sages, Jesuit missionaries, yogis.

Figures of yogis recur in manuscript paintings produced by the Mughal court. Some of these images are pure escapist fantasy, with handsome yogi princes devoutly tracking down sweethearts in Sufi romances. Other pictures have the specificity of photo-documents, as in the case of an extraordinary double-leaf 16th-century painting of a mortal fight between rival yogic sects. The skirmish, waged over bathing rights in a sacred river, was witnessed by the Mughal emperor Akbar, who described it to an artist, who in turn spares us none of the bloody details of yogi-on-yogi stabbings, spearings and decapitations.

The British, who succeeded the Mughals, lived in fear of yogic militancy and used art, among other means, to reduce their power. British photographic studios in 19th-century India turned out endless images of yogis as disheveled, half-clothed, ash-smeared freaks. On the one hand such pictures were given an ethnological spin, as a tool of science, or rather science as a form of surveillance. On the other, they fed the Western appetite for exoticism, presenting yogis as primitive poseurs and yoga itself as a primitive form of theater.

Such images, or versions of them, persisted well into the 20th century in Hollywood and in the popular press. At the same, India, in the buildup to independence, began to take yoga back, to reclaim it for modern, global use. This entailed making fundamental changes, scrubbing yoga clean of mysticism, and repositioning it in a secular, rational context: first in medicine, and then in a burgeoning culture of physical fitness and self-help therapy, where it rests today.

The fact is, yoga was always rational, and more so in its old, extremist forms than in its present domesticated version. How else would you characterize a spiritual discipline that directly and boldly addressed life’s most intractable problem, the persistence of suffering, and took practical, but radical steps to do something about it? To alter the rules of the existential game, it redefined the possible. What’s great about the Sackler show, apart from the pleasures of its images, is that it not only lets us see the history of that practice in action, but understand how radical it was — and is — and take that seriously.