Sentence:  The x-ray data did not permit Douglass to determine uniquely the space group , but a negative test for <WSD>piezoelectricity</WSD> led him to assume a center of symmetry . 
Meaning of the word marked with <WSD> tags:  electricity produced by mechanical pressure on certain crystals (notably quartz or Rochelle salt); alternatively, electrostatic stress produces a change in the linear dimensions of the crystal