Converse and disjunctive proportion
Duple and triple ratios and the rule of inverse proportion
A few lines of mirror writing at the head of an otherwise blank leaf treat 'converse' and 'disjunctive' proportion, using duple (8 to 4, 12 to 6) and triple ratios as examples. The note argues that if 4 is to 2 as 6 is to 3, then, taken the other way round, 2 to 4 and 3 to 6 form the converse relation. A library stamp of the Institut de France is impressed at lower right.
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Converse (inverse) proportion
Working with duple and triple ratios, the note states that if the step from 4 to 2 equals the step from 6 to 3, then reversing the terms gives 2 to 4 and 3 to 6 as the converse relation. It labels the arrangement 'disjunctive'.