Abstract

Contrary to what has been asserted or implied by Mach and more recent writers, the law of illumination and the study of photometry were not ignored in the years between Kepler's first enunciation of the former in 1609 and Bouguer's Essai on the latter in 1729. The law of illumination was in fact denied in 1613 by Aguilonius. It was probably rediscovered independently and certainly reformulated in more modern terms by Mersenne and Castelli in 1634, and by Boulliau in 1638. It was again formulated and this time demonstrated empirically by Montanari no later than 1676, and possibly as early as 1634 by Castelli. Although neither the law nor photometry were major concerns before Bouguer, they were not completely neglected either