The water from the fountain shoots into the air because water anywhere will run down if given a chance. To produce a fountain you must have a source of water supply for the fountain which is higher than the openings of the fountain out of which the water shoots. The water comes out of the holes in the fountain for the same reason that it comes out of the faucet in the kitchen or bath room. In the latter case the water comes from the waterworks reservoir in which the level of the water is much higher than the opening in the faucet in your home. Being higher the water in the reservoir is trying to get away through the pipes all the time and all the pipes leading from the reservoir are full of this water trying to get away. Just as soon as you turn the valve in the faucet the water comes out and runs down into the bowl. If you were to turn the opening of the faucet up instead of down as it is, the water would shoot up instead of down. Not very much, it is true, but it would act much like the water from the fountain. The reason it does not shoot up high in the air like a fountain is because the opening in the faucet is the same size as the opening in the little pipe which leads the water from the street into the house. If you would turn the opening of the faucet up and attach to it a pipe which made the opening much smaller (the size of the opening in the fountains), you would see the water shoot into the air just as it does from the fountain. When you reduce the size of the opening you increase the pressure of the water coming from the pipes in proportion to the reduction you have made in the size of the opening. Water from the fountain will not, however, shoot as high as the level of the water in the reservoir because, as soon as it leaves the pipes, it encounters the pressure of the air outside the pipes and the law of gravitation which pulls all things toward the center of the earth. It is not natural for water to shoot into the air as it does in a fountain. The only way water can go naturally is down, and it only goes up a little way from a fountain because of the pressure of the water in the pipes behind the openings in the pipes in the fountain. What Keeps a Balloon Up? A balloon stays up in the air, because of the air in it, together with the weight of the balloon, is less than an equal bulk of the air in which it floats. In former days of ballooning the balloons were filled with hot air and were then found to rise and stay up until the air inside of the balloon became of the same temperature as that in which it floated. When this stage was reached, the balloon itself would fall because the material of which it was made was denser than air. Today balloonists fill their balloons with gas which is lighter than air, even when as cool as the air in which they rise and are thus able to stay up a long time.