Doppler, Christian, 1803-1853.
Christian Doppler signed certificate, 1842.
Certificate signed by Doppler testifying that Joseph Kettner completed Doppler's secondary school algebra course.
Algebra -- Study and teaching.
Kettner, Joseph.
AIP-ICOS
American Institute of Physics. Niels Bohr Library & Archives. One Physics Ellipse, College Park, MD 20740, USA