13 until a position of the pipe 17 is found at which the amplitude of the signal p c is a maximum the resonance cavity is attuned to the frequency of the microwave generator with the pipe 17 in this position the pipe 17 is made of a material which has low dielectric losses for example aluminium oxide the parison 3 is heated up to a desired temperature in the alternating electric field through dipole losses see dubbel taschenbuch fur den machinenbau 15 th impression pp 1236 1237 the resonance frequency of the resonance cavity 13 changes continually owing to the presence of the glass parison 3 in the resonance cavity and the rising temperature of the parison the frequency of the alternating electric field is periodically adapted to the changing resonance frequency of the resonance cavity 13 so as to maintain an optimal energy transfer this is explained in more detail with reference to fig2 the alternating electric field is switched off when the glass parison 3 has the desired temperature the temperature may be measured by means of an infrared temperature gauge it is alternatively possible to determine empirically a certain heating up time during which the parison is to be heated after the alternating electric field has been switched off the mould 7 is moved towards the mould 5 a rim 23 of the mould 7 fits around the outside of the mould 5 and ensures the alignment of the mould 7 relative to the mould 5 the mould 7 presses the glass parison 3 into the shape determined by the.