The adiabatic heat produced in a sound field up to frequencies of 5000 cycles has been measured with a thermocouple. Similar thermocouples have been used to measure small intensities of radiation. The response of these sensitive couples depends upon the use of thin films of metal and the use of a.c. amplification. The couples have been made by cathodic sputtering of bismuth, antimony and tellurium on thin cellulose. A detailed account of their construction is presented.