Monge's Circle Theorem

The Gaspard Monge's Theorem about three circles in a plane states that the intersection points of the external tangents of each pair of circles are collinear. There are many proofs of this theorem, however, one of them is stunningly cute. It says that any configuration of three circles and their tangents in the Monge's theorem could be considered as the silhouettes of tubes connecting three equal spheres. Because the spheres could be at different distances, some look smaller, other bigger. When the tubes are extended to infinity their contours (i.e. the circles' tangents) converge to points on the horizon. As long as there is only one horizon, all three points happen to be collinear.

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[ElicaTeam]

@jotape1960 Every theorem is valid in a specific geometrical environment. For example, a triangle on a sphere may have three right angles, while this is not possible for a triangle in the plane.

[jotape1960]

Of course, it is intended to think the tangent lines extended into an infinite plane geometry. Some people talks about a non plane universe (astronomy issue). I guess this theorem isn't valid on a non plane geometry. Am I right? or Wrong? ???