This is a very good article about proper bowing technique and although we are instructed as beginners to try and keep the bow "Parallel" with the bridge when bowing, I think it has more to do with control of the bow rather than just blindly keeping it perfectly parallel with the bridge.

We are also taught to locate the hair in a place between the bridge and the end of the fingerboard for the best sound... but if you watch a professional play like Hillary or David you will see they are 'all over the strings' with the bowing on occasion. Of course they've been playing for decades whereas we (the students of FM) have for the most part been playing hours instead. So... understanding the relationship between bow hair placement, pressure, speed, angle, etc. are the root of musical sounds produced by the violin.

Enjoy the read...

It's just another chapter in your lessons for playing the violin.

http://www.violinist.com/blog/.....156/16836/