Imagine…when you walk, you start with right leg forward, then left leg, and then right, left, right, left…
so as the bow.
Down bow, then comes up bow, down, up, down, up…
If you don’t see any indication of bowing (direction) on the music, it means just ‘as it comes’ (each note is bowed up and then down successively) , as if you are walking. Right, left, right, left…Down, up, down, up… 🙂