Complex sentence: The obelisk on which this petition was engraved was brought into England by Mr. Bankes, and its hieroglyphics, compared with those of the Rosetta stone, threw great light upon the Egyptian phonetic alphabet.
Split into simpler sentences: The obelisk on which this petition was engraved was brought into England by Mr. Bankes. When its hieroglyphics were compared with those of the Rosetta stone, it threw great light upon the Egyptian phonetic alphabet.