Along with Scherrer, he developed powder X-ray diffraction analysis, and conceived the theory of X-ray scattering by gaseous molecules.  
His achievements include showing how sound waves in a liquid can behave like a diffraction grating, and he did work on adiabatic demagnetization.  Along with Scherrer, he developed powder X-ray diffraction analysis, and conceived the theory of X-ray scattering by gaseous molecules.  Earlier, he developed a theory of strong electrolytes with H?ckel and modified Einstein's theory of specific heats to include compressibility and expansivity.  FTP, identify this Dutch-born physicist for whom the unit of dielectric constant is named, the recipient of the Nobel Prize for Chemistry in 1936.
His achievements include showing how sound waves in a liquid can behave like a diffraction grating, and he did work on adiabatic demagnetization.  
Peter Debye or Petrus Josephus Wilhelmus Debije