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
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.