In my last gnome fortress I built a seismic telegraph and requested for traders several times, but nothing happened, not even any failure announcement. I've tried building it on soil, on rock, using stone or metal pistons, but everytime nothing happened. Viewing neighbouring civilization showed that there were one accessible gnome civilization. But no traders. As a result, for seven years of the fortress' history, there were no migrants except the first two waves. However, talking to birds and they told my gnomes "There are migrants off in the distance", but they never come. I set the population cap to 200, and my current population is a mere 26 (plus 3 automata). Am I doing something wrong? Is there any criteria for the traders and the migrants to come?