Much enjoyment can be had with magnetic coins and any steel magnet (bar, button or horseshoe), usually found at school or in the home.

Even a fridge magnet can amaze and can be used to check whether a coin is magnetic. The magnet on the back is often made of a ceramic material called "ferrite".

During the last fifty years a whole range of magnets made of ferrite have become available. They are used in great quantities in electronics and in electrical engineering. The rubber-like magnetic seal on the inside of a refrigerator door also contains such material.

Today, even stronger magnets described as "rare-earth" or "neodymium" or "neo" magnets are being sold by specialist suppliers and are becoming increasingly common.

But strong magnets can be dangerous - they must be handled very carefully.

• Large strong magnets can cause serious personal injury through their powerful attraction with each other and other metallic objects.
• Magnets can effect electronic apparatus and magnetic items such as tapes, discs, and cards if they are sufficiently strong and get sufficiently close.
• Very small strong magnets, not permanently attached to a larger object, can also cause problems by getting into magnetically sensitive places undetected.
• Both ferrite and neo magnets are also easily chipped. It is often wise to ensure they are covered with some non-magnetic material.

In addition to its overall strength, the shape and physical size of a magnet, and how it is magnetised also determines how coins interact with them and with each other.

• Size for size, ferrite magnets are relatively cheap compared to strong steel magnets. Neo magnets are presently much more expensive.
• Compared to common steel magnets, ferrite magnets also have the advantage that they do not demagnetise easily.

After taking all these factors into account the most suitable magnets to use, as an addition, or as an alternative, to conventional steel magnets, for enjoying the fascinating properties of magnets and magnetic coins are still probably those similar to the "magic penny" magnets described and used in the book "Investigating Magnetism". ie

• rectangular block strontium ferrite magnets, approximately 50x20x20mm. (two similar thinner flat magnets 50x20x10mm, or four 50x20x5mm attached one on top of the other, can produce similar effects).
• magnetised so that the conventional "poles" are situated at the centre of opposite long sides, rather than on the smaller opposite ends.

• covered in a thin non-magnetic material such as tape, plastic, wood, aluminium or non-magnetic stainless steel.

Investigating how magnetic coins interact with electromagnets, from the most simple to the electronically controlled, can also be hugely stimulating, and again can result in some spectacular effects.

But please, before working with any magnet ensure you are aware of any safety hazards involved. If you are not sure: DO NOT USE.