I am getting data from a ping sensor on a Arduino Uno. On the linux side of Galileo I run the command cat /dev/ttyS0 and the values are displayed just fine. Here are my connection from Galileo to Arduino Uno
Arduino Uno Galileo Pin 0 - RX Pin 1 - TX Pin 1 - TX Pin 0 - RX GND GDN
I am running the ping sensor sketch on the Arduino Uno, and writing the output to Serial. Serial is displaying the values on the Serial monitor and writing to TX. So on the python script running on your Galileo Board you will need to read from /dev/ttyS0. Can you paste your Arduino sketch so i can try to replicate the behavior of your code.? Also what sensor are you using?