Definition: Def. 11.24: Similar Cones, Similar Cylinders
Similar cones and cylinders are those for which the axes (of the cones, respectively axes of the cylinders) and the diameters of the bases (of the cones, respectively bases of the cylinders) are proportional.
Modern Formulation
Please refer to the modern definition of similarity, which is valid for Euclidean spaces of any dimension and for all geometrical objects contained in them.
Mentioned in:
Proofs: 1
Propositions: 2
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References
Adapted from (subject to copyright, with kind permission)
 Fitzpatrick, Richard: Euclid's "Elements of Geometry"
Adapted from CC BYSA 3.0 Sources:
 Prime.mover and others: "Pr∞fWiki", https://proofwiki.org/wiki/Main_Page, 2016