Singular experiment.
--Take a round piece of pasteboard and insert it in a quill open at both ends, and lay this on another piece of pasteboard of the same shape, in which is stuck a pin, so that the pin will enter the quill. Blow through the quill as hard as you may, but the lower piece cannot be blown off.A common spool, such as is used for sewing cotton, forms a suitable apparatus for trying this wonderful experiment. Take a bit of smooth writing paper a little larger than the head of the spool, and run a pin through the paper and into the bore of the spool. Now, by blowing down it will be found impossible to blow the paper off. By observing closely, it will be seen that the paper does not quite touch the head of the spool. It is, of course, necessary to hold the paper up with your hand until you begin to blow.
The explanation is this: When currents of air are established, radiating from the central tube horizontally between the disk and the paper, the greater area of the disk as compared with that of the tube causes the air above the paper to be rarified, when the pressure of the air below, not being counterbalanced, holds the paper up. The pin acts as an anchor to prevent the paper from being blown away horizontally.
