--- European finance ministers seem to think there's a fair chance George Osborne will end up as chancellor, because a number of them have been in touch with him, to SOUND HIM OUT on the euro bailout.
(BBC News)
Did you know?
sound out phrasal verb
- to carefully discover what someone thinks or knows
(Cambridge Dictionary of American Idioms)
--- To sound someone out is to ask them questions in order to obtain information or an opinion. The use of the verb sound in this context likely stems from the maritime sense of sounding, which is measuring the depth of a mass of water like the ocean.
This is usually done with sonar, which measures the length of time it takes for sound to travel to a reflecting surface and back. Think of "sound out" as a human-to-human form of sonar, only without the characteristic "ping."
Speaking of "ping," this is what the Internet industry refers to bouncing a small packet of data off of a remote network address to see how long the packet takes to make the round trip. It is one of the most common utilities for testing Internet connections.