High frequency (`violet ray') apparatus
1920-1940
1920-1940
1950-1960
1925-1950
1920-1940
before 1966
1925-1940
1925-1935
1903-1904
1903-1904
1880-1910
1890-1950
1903-1904
1920
before 1966
1920-1950
1903-1904
1903-1904
1903-1904
1920