[Melilot Brandybuck]

In FoTR, Ch.2, Gandalf relates to Frodo his search for Gollum. He mentions that Gollum, in his wanderings, had suddenly headed south to Mordor, and he was in fact answering a silent summons issued by Sauron, that called those who were or had been under the power of the ring. So, why wasn't Bilbo compelled to answer this summons? Gollum had not possessed The Ring for several years, and Gandalf mentions that he did not use it much during his time under the Misty Mountains. Bilbo had had the ring for many years, and we know he occasionally used it. Was it just that hobbits were made of tougher stuff? But Gandalf states that Gollum's origins and the hobbit's origins were similar. It would have been much handier for Sauron had Bilbo arrived at the gates of Mordor complete with ring.