# CONVERSION

, or Convertendo, is when there are four proportionals, and it is inferred, that the first is to its excess above the 2d, as the third to its excess above the 4th: according to Euclid, lib. 5, def. 17.

Thus, if it be | 8 : 6 :: 4 : 3, |

then convertendo, or by conversion, | 8 : 2 :: 4 : 1, |

Or if there be | a : b :: c : d, |

then convertendo, or by conversion, | a : a-b :: c : c-d. |