Members of the Underground Railroad often used specific terms, based on the metaphor of the railway. For example:  The Big Dipper (whose "bowl" points to the North Star) was known as the drinkin' gourd. The Railroad was often known as the "freedom train" or "Gospel train", which headed towards "Heaven" or "the Promised Land", i.e., Canada. William Still, sometimes called "The Father of the Underground Railroad", helped hundreds of slaves to escape (as many as 60 a month), sometimes hiding them in his Philadelphia home. He kept careful records, including short biographies of the people, that contained frequent railway metaphors. He maintained correspondence with many of them, often acting as a middleman in communications between escaped slaves and those left behind. He later published these accounts in the book "The Underground Railroad: Authentic Narratives and First-Hand Accounts" (1872), a valuable resource for historians to understand how the system worked and learn about individual ingenuity in escapes. According to Still, messages were often encoded so that they could be understood only by those active in the railroad. For example, the following message, "I have sent via at two o'clock four large hams and two small hams", indicated that four adults and two children were sent by train from Harrisburg to Philadelphia. The additional word "via" indicated that the "passengers" were not sent on the usual train, but rather via Reading, Pennsylvania. In this case, the authorities were tricked into going to the regular location (station) in an attempt to intercept the runaways, while Still met them at the correct station and guided them to safety. They eventually escaped either to the North or to Canada, where slavery had been abolished during the 1830s. To reduce the risk of infiltration, many people associated with the Underground Railroad knew only their part of the operation and not of the whole scheme. "Conductors" led or transported the fugitives from station to station. A conductor sometimes pretended to be a slave in order to enter a plantation. Once a part of a plantation, the conductor would direct the runaways to the North. Slaves traveled at night, about to each station. They rested, and then a message was sent to the next station to let the station master know the runaways were on their way. They would stop at the so-called "stations" or "depots" during the day and rest. The stations were often located in barns, under church floors, or in hiding places in caves and hollowed-out riverbanks.