Elliptical Clauses are grammatically incomplete in the sense that they are missing either the relative pronoun (dependent word) that normally introduces such a clause or something from the predicate in the second part of a comparison. The missing parts of the elliptical clause can be guessed from the context and most readers are not aware that anything is missing. In fact, elliptical clauses are regarded as both useful and correct, even in formal prose, because they are often elegant, efficient means of expression. (The omitted words are noted in brackets below).
In 1920 a debate took place between Harlow Shapley and Heber Curtis (the Great Debate ), concerning the nature of the Milky Way, spiral nebulae, and the dimensions of the Universe. To support his claim that the Great Andromeda Nebula is an external galaxy, Curtis noted the appearance of dark lanes resembling the dust clouds in the Milky Way, as well as the significant Doppler shift.