The bow is a very important part of the violin, indeed it can be worth as much as the fiddle. Some gold mounted bows made by a reputable maker could be worth more than $ 4000.
The tension of the bow is controlled by a screw in the nut of the bow. This can be made of ebony, but in more expensive bows can be made of tortoiseshell or ivory, adorned with inlaid mother of pearl. From the nut there is a long thin screw which goes into the nut of the bow and above this is where you hold. The nut sticks out a bit from your fingers. The screw goes into the wood of the bow which has been bored to take it, and that goes through the little nit.
Just tighten this to get the correct tension of the bow. Here again some people like to play with a very tight bow and some people like to play with less tension in the bow hair. Nobody, of course, plays with an absolutely flat bow. You would get no sound at all! Which maybe your neighbors would like, but its not a good way to learn!
The bow hair, of course, needs rosin, a solid residue left after turpentine has been distilled. You don’t have to put on a lite, but what you do need to do is to put enough on so that you can draw the bow across the strings with a certain amount of pressure that will give you a note. If there is no rosin on the bow at all it will just float over the top of the strings, it is the rosin which grips that part of the string you are bowing on to produce a note.
You should put rosin on your bow every time you play – just a couple of rubs of rosin should be sufficient. When you have a bow rehaired or when you buy a new one from a dealer, he will rosin the bow for you in its initial stage with its brand-net untouched hair. When you get the bow first and the hair has been already used, you will need to give it three or four rubs full-length on a piece of rosin, almost like ‘playing’ the piece of rosin.