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Peer reviewed: True, Funder: The Carlsberg Foundation, In this essay, I study the contested role of magnification as an observational strategy in the generation theories of William Harvey and René Descartes. During the seventeenth century, the grounds under the discipline of anatomy were shifting as knowledge was increasingly based on autopsia and observation. Likewise, new theories of generation were established through observations of living beings in their smallest state. But the question formed: was it possible to extend vision all the way down to the first points of life? Arguing that the potential of magnification hinged on the metaphysics of living matter, I show that Harvey did not consider observational focus on the material composition of blood and embryos to be conducive to knowledge of living bodies. To Harvey, generation was caused by immaterial, and thus in principle invisible, forces that could not be magnified. Descartes, on the other hand, believed that access to the subvisible scale of natural bodies was crucial to knowledge about their nature. This access could be granted through rational introspection, but possibly also through powerful microscopes. The essay thus ends with a reflection on the importance of Cartesian corpuscularianism for the emergence of microscopical anatomy in seventeenth-century England.