The Leonardo Notebook - Pages 11 and 12
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Studies of reflections from concave mirrors ff.86v-87
In addition to a fascination with the abstract geometry of the patterns of reflection, Leonardo was also interested in the potential utility of concave mirrors as sources of heat.
On the right-hand page Leonardo is arguing that in concave mirrors of equal diameter, the one which has a shallower curve will concentrate the highest number of reflected rays on to a focal point, and 'as a consequence, it will kindle a fire with greater rapidity and force'.