A description is presented of a 24 GHz microwave transmission apparatus having a sensitivity of approximately 10−17W in a 10 Hz bandwidth, and of a novel bolometric method for the measurement of ferromagnetic resonance lineshapes in metals. The role played by the cavity modes in transmission and absorption measurements is discussed. In addition, we have discussed the measurement of the effective dc field in disc-shaped ferromagnetic samples and the measurement of the microwave frequency.