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  • The Telescope as Prosthesis
  • Anna Henchman (bio)

In 1845, William Parsons, the Earl of Rosse, completed a 56-foot long reflector telescope with a 6-foot wide mirror that would remain the largest telescope in the world until 1917. Telescopes are not conventionally described as prostheses, a word that tends to refer to devices that supplement a lack, replacing or augmenting a part of the body that is in some way missing or defective. Yet by adding to what the human body can do, telescopes hold strong structural similarities to such prosthetic devices as artificial hands, legs, or teeth: they extend human vision into distant regions of space, supplementing the capacities of a healthy eye and enabling a vastly intensified level of perception.

The question of whether telescopes are best thought of as prosthetic devices or merely as tools sheds light on longstanding debates about the relative importance of scientific instruments and the human beings who use them to advance science. Any account of the role of telescopes in the history of astronomy tends, at least implicitly, to be based on some conception of the relationship between eye and telescope, and, by extension, the relationship between human being and machine. Writings on astronomy usually emphasize either the abilities of the astronomer looking through the glass or the power of the telescope itself. Frequently those writers who focus on the power of the telescope stress the [End Page 27] relative deficiencies of unassisted human vision, characterizing human vision as having the kind of lack that would require a prosthetic device.

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Fig. 1.

Lord Rosse's reflector telescope, with a 6-foot wide mirror, built in the 1840s. By permission of the National Maritime Museum, Greenwich, London.

Lorraine Daston and Peter Galison's 2007 Objectivity explores the assumptions behind dueling conceptions of the scientist in the late eighteenth and nineteenth centuries. The authors contrast faith in "mechanical objectivity," which places instruments and machines at the centre of scientific inquiry, with the ideal of the scientist as learned seer. The synthesizing mind of the seer absorbs extensive empirical data and then extrapolates from that data the image of an ideal type. By contrast, those who begin to doubt the objectivity of the human eye and mind rely increasingly on information gathered by machines. In this model, the impersonality of the machine becomes preferable to the unpredictable human observer, and mechanical instruments are valued for their abilities to make up for specific lacks in human vision or in the judgment of individual observers. This is a helpful framework to apply to discussions of telescopes, because it sheds light on why one writer might place so much importance on the role of the astronomer, for whom the telescope is simply a tool, while another imagines the telescope to work almost without a human agent.

William Herschel (1738-1822), John Keats's famous "watcher of the skies," in many ways conforms to the model of the scientist as seer ("On First Looking [End Page 28] into Chapman's Homer," line 9). Herschel emphasizes the importance of human knowledge and experience in the collaboration between eye and telescope. For much of the eighteenth century, the most important developments in astronomy had been the result of theoretical, mathematical calculations rather than observation through a telescope.1 Newton's 1687 explanation of the universal law of gravitation holding the solar system together had depended on calculations and theory rather than empirical research. Starting in the 1780s, however, Herschel placed empirical observation through telescopes, rather than mathematical theory, back at the centre of the study of astronomy. He virtually invented stellar astronomy by developing a series of telescopes that made it possible to study the stellar universe—as opposed to the contents of the solar system—in unprecedented detail.2 Herschel's theory that stars began as amorphous nebulae and gradually evolved into systems of stars, planets, and moons was based on decades of meticulous empirical observation.

While his work relied heavily on telescopic observation, Herschel emphasized the importance of training the eye and mind over the powers of the telescope. In a 1782 letter, he characterized his own interpretive ability as the...


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