Abstract: Scientific apparatus and a method are described for observing simultaneously both structural and thermodynamic properties of materials. An X-ray diffractometer and a thermal analyzer and mounted to cooperate and coact on the same sample and to complete a meaningful analysis in a very few minutes. The diffractometer is equipped with a rapid position-sensitive detector connected to a multichannel analyzer to record and display X-ray diffraction data from the sample over an angle of 20.degree. (two theta) or more. The thermal analyzer is preferably a differential scanning calorimeter. By correlating X-ray diffraction and thermal data taken simultaneously while the sample is passing through a range of temperatures and/or environments, structural changes corresponding to thermal events can be identified and elucidated.