jb mentioned how to raise the water level in the "tank" but remember that you should be at least a quarter inch or more below the overflow in the tank.
Your question asked about the bowl. They are made so they have their own trap. The water level can never be any higher than the weir of the trap(or else it will run over and down into the drain). Some toilets show the curve of the trap from the outside and you can visualize the water level line before it flows over the weir. Check this out. If you can't tell externally then you may need to pull it.
Also sometimes string and other things get caught in the toilet trap which acts like a syphon or a wick and wicks water out of the bowl and down the drain. If this is the case, then after a flush the water should hold at the normal level for a little bit before wicking over. An old toilet like that will have a ring around the bowl that corresponds to the natural level of the bowl so you can tell if what you have is abnormal or not. Try pouring a gallon of water or so into it and see how it does.