Empiricism Without the Senses: How the Instrument Replaced the Eye

On receiving news of Galileo’s observations of the four satellites of Jupiter and the rugged face of the moon through his newly invented perspicillum, Kepler in great excitement exclaimed: Therefore let Galileo take his stand by Kepler’s side. Let the former observe the moon with his face turned skyward, while the latter studies the sun by looking down at a screen (lest the lens injure his eyes). Let each employ his own device, and from this partnership may there some day arise an absolutely perfect theory of the distances. This Hollywood-like scene of the two astronomers marching hand in hand toward the dawn of a new scientific era was no attempt by Kepler to appropriate Galileo’s success or to diminish the novelty of the telescope. On the contrary, Kepler repeatedly asserted how short sighted he was in misjudging the potential for astronomical observations inherent in lenses, and how radically Galileo’s instrument transformed the science of astronomy. It was a deep sense of recognition that beyond their different scientific temperaments and projects, they shared a common agenda of a new mode of empirical engagement with the phenomenal world: the instrument. For Kepler and Galileo, empirical investigation was no longer a direct engagement with nature, but an essentially mediated endeavor. The new instruments were not to assist the human senses, but to replace them