A transducer has been developed to detect changes in position of a balance beam. Its operation is based upon a differential capacitor. Variations in capacitance are made to produce directly a d.c. voltage corresponding in sign to the sense of deflexion of the balance beam. The construction of the transducer is described, and its application in automatic apparatus for thermogravimetric analysis is illustrated by results obtained on the dehydration of copper sulphate and the decomposition of quinoline phosphomolybdate.The sensitivity of the instrument can be varied in nine steps to give full-scale deflexions from 10 to 5000 mg. An accuracy of about 1.5 mg or 0.75% of full scale was obtained for the 200 mg range.