a thermal cycling device consisting of a plate containing a plurality of wells to hold liquid and a lid that covers the plate and contains a number of “ pins ” that insert into the wells of the plate to control the temperature of the sample in the well . biological , chemical or other samples are placed into the wells of the plate and the lid is placed on the plate with the pins inserted into or in the proximity of the sample . the lid , the outer surface of which may be copper clad and in direct contract with the pins , is heated or cooled , rapidly and uniformly heating or cooling the biological samples . the temperature of the sample can be rapidly and uniformly cycled and is particularly useful for the amplification of dna via the polymerase chain reaction .