There are several ways of doing this, some requiring considerable practice.
The following is the simplest.
Float on the surface of the water a cigarette paper; place the pin upon it; leave the paper to sink to the bottom when it has become soaked, and the pin will float without any difficulty, for on either side of the pin the water takes the convex shape before mentioned, thus displacing sufficient water to allow the pin to float.
In order to hide from the spectators the stratagem you have employed, gently remove the paper before showing them the floating pin.
Joined by Air
The [picture] below is not taken from a prospectus advertising cement for joining glass and porcelain, but is simply used to show how atmospheric pressure may be utilized for joining glasses and plates.
In order to accomplish this it is necessary to form a vacuum, but as an air-pump is not at the disposal of every boy a partial vacuum must suffice.
To obtain this partial vacuum suspend a glass from the ceiling, or any other suitable place, by means of a string, and under it burn a piece of paper. This will cause the air it contains to expand. Immediately afterwards place the plate over the mouth of the glass, and it will adhere quite firmly.
In order to prevent the entrance of any external air, and thus destroy the vacuum, the edges of the glass may be smeared with tallow.
Now, how is it that the glass and plate are so easily fixed? Well, directly the hot air contained in the glass comes in contact with the cold surface of the plate, the air contracts, and as the plate prevents the entrance of any more air, a partial vacuum is formed within the glass.