Page:The story of the comets.djvu/217

XI.

of Perihelion Passage is generally not given, but left to be inferred from the other.

For a parabolic orbit e is always 1⋅0 (or Unity) ; and in that case the elements are frequently given by stating T,, , i, and log. q. Here has been replaced by:—

which is counted on the comet's orbit, backward, from the