Throughout the book a bain-marie (water bath) is used to melt chocolate, warm eggs for meringue and sponges, etc. It is also a useful method while tempering chocolate if you do not have a porringer pot.
Set a bowl over a saucepan of simmering water. It is important that the base of the bowl does not touch the water.
An ice bain-marie is used to cool mixtures down rapidly.